Merge branch 'trunk' of rtfeldman/roc into editor_refactor

.gitignore

@@ -1,4 +1,5 @@
 target
+zig-cache
 .direnv
 *.rs.bk
 
@@ -7,3 +8,4 @@ vgcore.*
 
 #editors
 .idea/
+

BUILDING_FROM_SOURCE.md

@@ -92,6 +92,8 @@ Now with nix installed you just need to run one command:
 
 > This may not output anything for a little while. This is normal, hang in there. Also make sure you are in the roc project root.
 
+> Also, if you're on NixOS you'll need to enable opengl at the system-wide level. You can do this in configuration.nix with `hardware.opengl.enable = true;`. If you don't do this, nix-shell will fail!
+
 You should be in a shell with everything needed to build already installed. Next run:
 
 `cargo run repl`

Cargo.lock

@@ -2583,6 +2583,7 @@ dependencies = [
  "roc_can",
  "roc_collections",
  "roc_constrain",
+ "roc_fmt",
  "roc_gen",
  "roc_load",
  "roc_module",

cli/src/repl/eval.rs

@@ -189,6 +189,11 @@ fn jit_to_ast_help<'a>(
             Content::Structure(FlatType::RecursiveTagUnion(_, _, _)) => {
                 todo!("print recursive tag unions in the REPL")
             }
+            Content::Alias(_, _, actual) => {
+                let content = env.subs.get_without_compacting(*actual).content;
+
+                jit_to_ast_help(env, lib, main_fn_name, layout, &content)
+            }
             other => unreachable!("Weird content for Union layout: {:?}", other),
         },
         Layout::RecursiveUnion(_) | Layout::RecursivePointer => {

cli/tests/helpers.rs

@@ -89,6 +89,25 @@ pub fn run_with_valgrind(args: &[&str]) -> (Out, String) {
 
     cmd.arg("--tool=memcheck");
     cmd.arg("--xml=yes");
+
+    // If you are having valgrind issues on MacOS, you may need to suppress some
+    // of the errors. Read more here: https://github.com/rtfeldman/roc/issues/746
+    if let Some(suppressions_file_os_str) = env::var_os("VALGRIND_SUPPRESSIONS") {
+        match suppressions_file_os_str.to_str() {
+            None => {
+                panic!("Could not determine suppression file location from OsStr");
+            }
+            Some(suppressions_file) => {
+                let mut buf = String::new();
+
+                buf.push_str("--suppressions=");
+                buf.push_str(suppressions_file);
+
+                cmd.arg(buf);
+            }
+        }
+    }
+
     cmd.arg(format!("--xml-file={}", filepath));
 
     for arg in args {

cli/tests/repl_eval.rs

@@ -87,6 +87,11 @@ mod repl_eval {
         expect_success("1.1 + 2", "3.1 : F64");
     }
 
+    #[test]
+    fn num_rem() {
+        expect_success("299 % 10", "Ok 9 : Result Int [ DivByZero ]*");
+    }
+
     #[test]
     fn bool_in_record() {
         expect_success("{ x: 1 == 1 }", "{ x: True } : { x : Bool }");

compiler/build/Cargo.toml

@@ -54,3 +54,8 @@ maplit = "1.0.1"
 indoc = "0.3.3"
 quickcheck = "0.8"
 quickcheck_macros = "0.8"
+
+[features]
+target-arm = []
+target-aarch64 = []
+target-webassembly = []

compiler/build/src/link.rs

@@ -42,12 +42,25 @@ pub fn link(
 pub fn rebuild_host(host_input_path: &Path) {
     let c_host_src = host_input_path.with_file_name("host.c");
     let c_host_dest = host_input_path.with_file_name("c_host.o");
+    let zig_host_src = host_input_path.with_file_name("host.zig");
     let rust_host_src = host_input_path.with_file_name("host.rs");
     let rust_host_dest = host_input_path.with_file_name("rust_host.o");
     let cargo_host_src = host_input_path.with_file_name("Cargo.toml");
     let host_dest = host_input_path.with_file_name("host.o");
 
     let env_path = env::var("PATH").unwrap_or_else(|_| "".to_string());
+
+    if zig_host_src.exists() {
+        // Compile host.zig
+        let output = Command::new("zig")
+            .env_clear()
+            .env("PATH", &env_path)
+            .args(&["build-obj", zig_host_src.to_str().unwrap()])
+            .output()
+            .unwrap();
+
+        validate_output("host.zig", "zig", output);
+    } else {
         // Compile host.c
         let output = Command::new("clang")
             .env_clear()
@@ -62,6 +75,7 @@ pub fn rebuild_host(host_input_path: &Path) {
             .unwrap();
 
         validate_output("host.c", "clang", output);
+    }
 
     if cargo_host_src.exists() {
         // Compile and link Cargo.toml, if it exists
@@ -132,15 +146,15 @@ pub fn rebuild_host(host_input_path: &Path) {
             .unwrap();
 
         validate_output("rust_host.o", "rm", output);
-    } else {
+    } else if c_host_dest.exists() {
-        // Clean up rust_host.o
+        // Clean up c_host.o
         let output = Command::new("mv")
             .env_clear()
             .args(&[c_host_dest, host_dest])
             .output()
             .unwrap();
 
-        validate_output("rust_host.o", "mv", output);
+        validate_output("c_host.o", "mv", output);
     }
 }
 

compiler/build/src/target.rs

@@ -41,7 +41,7 @@ pub fn arch_str(target: &Triple) -> &'static str {
 
             "x86-64"
         }
-        Architecture::Aarch64(_) => {
+        Architecture::Aarch64(_) if cfg!(feature = "target-aarch64") => {
             Target::initialize_aarch64(&InitializationConfig::default());
             "aarch64"
         }

compiler/builtins/bitcode/build.zig

@@ -38,7 +38,7 @@ pub fn build(b: *Builder) void {
     const ir_to_bitcode = b.addSystemCommand(&[_][]const u8{
         "llvm-as-10",
         ir_out_file,
-        bitcode_path_arg
+        bitcode_path_arg,
     });
 
     const bicode = b.step("bc", "Build LLVM ir and convert to bitcode");

compiler/builtins/bitcode/run-tests.sh

@@ -1,6 +1,9 @@
 #!/bin/bash
 
-set -eux
+set -euxo pipefail
 
 # Test every zig
-find src/*.zig -type f -exec zig test {} \;
+find src/*.zig -type f -print0 | xargs -n 1 -0 zig test --library c
+
+# fmt every zig
+find src/*.zig -type f -print0 | xargs -n 1 -0 zig fmt --check

compiler/builtins/bitcode/src/helpers/grapheme.zig

@@ -4,7 +4,7 @@ const expectEqual = std.testing.expectEqual;
 
 // This whole module is a translation of grapheme breaks from
 // the https://github.com/JuliaStrings/utf8proc library.
-// Thanks so much to those developer!
+// Thanks so much to those developers!
 //
 // The only function this file exposes is `isGraphemeBreak`
 //
@@ -49,8 +49,7 @@ test "Bound Class" {
 fn graphemeBreakSimple(lbc: BoundClass, tbc: BoundClass) bool {
     const lbc_u8 = @enumToInt(lbc);
     const tbc_u8 = @enumToInt(tbc);
-  return (
+    return (if (lbc_u8 == @enumToInt(BoundClass.START)) // GB1
-    if (lbc_u8 == @enumToInt(BoundClass.START)) // GB1
         true
     else if (lbc_u8 == @enumToInt(BoundClass.CR) and tbc_u8 == @enumToInt(BoundClass.LF)) // GB3
         false
@@ -71,8 +70,7 @@ fn graphemeBreakSimple(lbc: BoundClass, tbc: BoundClass) bool {
     else if (lbc_u8 == @enumToInt(BoundClass.REGIONAL_INDICATOR) and tbc_u8 == @enumToInt(BoundClass.REGIONAL_INDICATOR)) // GB12/13 (requires additional handling below)
         false
     else // GB999
-      true
+        true);
-  );
 }
 
 // https://github.com/JuliaStrings/utf8proc/blob/master/utf8proc.c#L291
@@ -151,11 +149,7 @@ test "codepointToBoundClass: invalid" {
 //                 which require this state will not be applied, essentially matching the rules in
 //                 Unicode 8.0.0.
 pub fn isGraphemeBreak(codePoint1: u21, codePoint2: u21, opt_state_ptr: *?BoundClass) bool {
-  return graphemeBreakExtended(
+    return graphemeBreakExtended(codepointToBoundClass(codePoint1).*, codepointToBoundClass(codePoint2).*, opt_state_ptr);
-    codepointToBoundClass(codePoint1).*,
-    codepointToBoundClass(codePoint2).*,
-    opt_state_ptr
-  );
 }
 
 // https://github.com/JuliaStrings/utf8proc/blob/master/utf8proc_data.c

compiler/builtins/bitcode/src/main.zig

@@ -4,28 +4,36 @@ const testing = std.testing;
 
 // Num Module
 const num = @import("num.zig");
-comptime { exportNumFn(num.atan, "atan"); }
+comptime {
-comptime { exportNumFn(num.isFinite, "is_finite"); }
+    exportNumFn(num.atan, "atan");
-comptime { exportNumFn(num.powInt, "pow_int"); }
+    exportNumFn(num.isFinite, "is_finite");
-comptime { exportNumFn(num.acos, "acos"); }
+    exportNumFn(num.powInt, "pow_int");
-comptime { exportNumFn(num.asin, "asin"); }
+    exportNumFn(num.acos, "acos");
+    exportNumFn(num.asin, "asin");
+}
 
 // Str Module
 const str = @import("str.zig");
-comptime { exportStrFn(str.strSplitInPlace, "str_split_in_place"); }
+comptime {
-comptime { exportStrFn(str.countSegments, "count_segments"); }
+    exportStrFn(str.strSplitInPlace, "str_split_in_place");
-comptime { exportStrFn(str.countGraphemeClusters, "count_grapheme_clusters"); }
+    exportStrFn(str.countSegments, "count_segments");
-comptime { exportStrFn(str.startsWith, "starts_with"); }
+    exportStrFn(str.countGraphemeClusters, "count_grapheme_clusters");
+    exportStrFn(str.startsWith, "starts_with");
+    exportStrFn(str.endsWith, "ends_with");
+    exportStrFn(str.strConcat, "concat");
+    exportStrFn(str.strNumberOfBytes, "number_of_bytes");
+    exportStrFn(str.strFromInt, "from_int");
+}
 
 // Export helpers - Must be run inside a comptime
-fn exportBuiltinFn(comptime fn_target: anytype, comptime fn_name: []const u8) void {
+fn exportBuiltinFn(comptime func: anytype, comptime func_name: []const u8) void {
-    @export(fn_target, .{ .name = "roc_builtins." ++ fn_name, .linkage = .Strong  });
+    @export(func, .{ .name = "roc_builtins." ++ func_name, .linkage = .Strong });
 }
-fn exportNumFn(comptime fn_target: anytype, comptime fn_name: []const u8) void {
+fn exportNumFn(comptime func: anytype, comptime func_name: []const u8) void {
-    exportBuiltinFn(fn_target, "num." ++ fn_name);
+    exportBuiltinFn(func, "num." ++ func_name);
 }
-fn exportStrFn(comptime fn_target: anytype, comptime fn_name: []const u8) void {
+fn exportStrFn(comptime func: anytype, comptime func_name: []const u8) void {
-    exportBuiltinFn(fn_target, "str." ++ fn_name);
+    exportBuiltinFn(func, "str." ++ func_name);
 }
 
 // Run all tests in imported modules

compiler/builtins/bitcode/src/str.zig

@@ -7,33 +7,36 @@ const expect = testing.expect;
 extern fn malloc(size: usize) ?*u8;
 extern fn free([*]u8) void;
 
-const RocStr = struct {
+const RocStr = extern struct {
     str_bytes: ?[*]u8,
     str_len: usize,
 
     pub fn empty() RocStr {
         return RocStr{
             .str_len = 0,
-            .str_bytes = null
+            .str_bytes = null,
         };
     }
 
     // This takes ownership of the pointed-to bytes if they won't fit in a
     // small string, and returns a (pointer, len) tuple which points to them.
     pub fn init(bytes: [*]const u8, length: usize) RocStr {
-        const rocStrSize = @sizeOf(RocStr);
+        const roc_str_size = @sizeOf(RocStr);
 
-        if (length < rocStrSize) {
+        if (length < roc_str_size) {
             var ret_small_str = RocStr.empty();
             const target_ptr = @ptrToInt(&ret_small_str);
             var index: u8 = 0;
+
+            // TODO isn't there a way to bulk-zero data in Zig?
             // Zero out the data, just to be safe
-            while (index < rocStrSize) {
+            while (index < roc_str_size) {
                 var offset_ptr = @intToPtr(*u8, target_ptr + index);
                 offset_ptr.* = 0;
                 index += 1;
             }
 
+            // TODO rewrite this into a for loop
             index = 0;
             while (index < length) {
                 var offset_ptr = @intToPtr(*u8, target_ptr + index);
@@ -42,24 +45,38 @@ const RocStr = struct {
             }
 
             // set the final byte to be the length
-            const final_byte_ptr = @intToPtr(*u8, target_ptr + rocStrSize - 1);
+            const final_byte_ptr = @intToPtr(*u8, target_ptr + roc_str_size - 1);
             final_byte_ptr.* = @truncate(u8, length) ^ 0b10000000;
 
             return ret_small_str;
         } else {
-            var new_bytes: [*]u8 = @ptrCast([*]u8, malloc(length));
+            var result = allocateStr(u64, InPlace.Clone, length);
 
-            @memcpy(new_bytes, bytes, length);
+            @memcpy(@ptrCast([*]u8, result.str_bytes), bytes, length);
+
+            return result;
+        }
+    }
+
+    // This takes ownership of the pointed-to bytes if they won't fit in a
+    // small string, and returns a (pointer, len) tuple which points to them.
+    pub fn withCapacity(length: usize) RocStr {
+        const roc_str_size = @sizeOf(RocStr);
+
+        if (length < roc_str_size) {
+            return RocStr.empty();
+        } else {
+            var new_bytes: [*]u8 = @ptrCast([*]u8, malloc(length));
 
             return RocStr{
                 .str_bytes = new_bytes,
-                .str_len = length
+                .str_len = length,
             };
         }
     }
 
-    pub fn drop(self: RocStr) void {
+    pub fn deinit(self: RocStr) void {
-        if (!self.is_small_str()) {
+        if (!self.isSmallStr()) {
             const str_bytes: [*]u8 = self.str_bytes orelse unreachable;
 
             free(str_bytes);
@@ -83,17 +100,16 @@ const RocStr = struct {
             return false;
         }
 
-        const self_bytes_nonnull: [*]const u8 = self_bytes_ptr orelse unreachable;
-        const other_bytes_nonnull: [*]const u8 = other_bytes_ptr orelse unreachable;
         const self_u8_ptr: [*]const u8 = @ptrCast([*]const u8, &self);
         const other_u8_ptr: [*]const u8 = @ptrCast([*]const u8, &other);
-        const self_bytes: [*]const u8 = if (self_len < @sizeOf(RocStr)) self_u8_ptr else self_bytes_nonnull;
+        const self_bytes: [*]const u8 = if (self.isSmallStr() or self.isEmpty()) self_u8_ptr else self_bytes_ptr orelse unreachable;
-        const other_bytes: [*]const u8 = if (other_len < @sizeOf(RocStr)) other_u8_ptr else other_bytes_nonnull;
+        const other_bytes: [*]const u8 = if (other.isSmallStr() or other.isEmpty()) other_u8_ptr else other_bytes_ptr orelse unreachable;
 
         var index: usize = 0;
 
         // TODO rewrite this into a for loop
-        while (index < self.str_len) {
+        const length = self.len();
+        while (index < length) {
             if (self_bytes[index] != other_bytes[index]) {
                 return false;
             }
@@ -104,7 +120,7 @@ const RocStr = struct {
         return true;
     }
 
-    pub fn is_small_str(self: RocStr) bool {
+    pub fn isSmallStr(self: RocStr) bool {
         return @bitCast(isize, self.str_len) < 0;
     }
 
@@ -116,17 +132,26 @@ const RocStr = struct {
 
         // Since this conditional would be prone to branch misprediction,
         // make sure it will compile to a cmov.
-        return if (self.is_small_str()) small_len else big_len;
+        return if (self.isSmallStr()) small_len else big_len;
     }
 
-    // Given a pointer to some memory of length (self.len() + 1) bytes,
+    pub fn isEmpty(self: RocStr) bool {
-    // write this RocStr's contents into it as a nul-terminated C string.
+        return self.len() == 0;
+    }
+
+    pub fn asU8ptr(self: RocStr) [*]u8 {
+        const if_small = &@bitCast([16]u8, self);
+        const if_big = @ptrCast([*]u8, self.str_bytes);
+        return if (self.isSmallStr() or self.isEmpty()) if_small else if_big;
+    }
+
+    // Given a pointer to some bytes, write the first (len) bytes of this
+    // RocStr's contents into it.
     //
-    // This is useful so that (for example) we can write into an `alloca`
+    // One use for this function is writing into an `alloca` for a C string that
-    // if the C string only needs to live long enough to be passed as an
+    // only needs to live long enough to be passed as an argument to
-    // argument to a C function - like the file path argument to `fopen`.
+    // a C function - like the file path argument to `fopen`.
-    pub fn write_cstr(self: RocStr, dest: [*]u8) void {
+    pub fn memcpy(self: RocStr, dest: [*]u8, len: usize) void {
-        const len: usize = self.len();
         const small_src = @ptrCast(*u8, self);
         const big_src = self.str_bytes_ptr;
 
@@ -135,12 +160,9 @@ const RocStr = struct {
 
         // Since this conditional would be prone to branch misprediction,
         // make sure it will compile to a cmov.
-        const src: [*]u8 = if (len < @sizeOf(RocStr)) small_src else big_src;
+        const src: [*]u8 = if (self.isSmallStr()) small_src else big_src;
 
         @memcpy(dest, src, len);
-
-        // C strings must end in 0.
-        dest[len + 1] = 0;
     }
 
     test "RocStr.eq: equal" {
@@ -157,8 +179,8 @@ const RocStr = struct {
         // TODO: fix those tests
         // expect(roc_str1.eq(roc_str2));
 
-        roc_str1.drop();
+        roc_str1.deinit();
-        roc_str2.drop();
+        roc_str2.deinit();
     }
 
     test "RocStr.eq: not equal different length" {
@@ -174,8 +196,8 @@ const RocStr = struct {
 
         expect(!roc_str1.eq(roc_str2));
 
-        roc_str1.drop();
+        roc_str1.deinit();
-        roc_str2.drop();
+        roc_str2.deinit();
     }
 
     test "RocStr.eq: not equal same length" {
@@ -192,25 +214,52 @@ const RocStr = struct {
         // TODO: fix those tests
         // expect(!roc_str1.eq(roc_str2));
 
-        roc_str1.drop();
+        roc_str1.deinit();
-        roc_str2.drop();
+        roc_str2.deinit();
     }
 };
 
+// Str.numberOfBytes
+
+pub fn strNumberOfBytes(string: RocStr) callconv(.C) usize {
+    return string.len();
+}
+
+// Str.fromInt
+
+pub fn strFromInt(int: i64) callconv(.C) RocStr {
+    // prepare for having multiple integer types in the future
+    return strFromIntHelp(i64, int);
+}
+
+fn strFromIntHelp(comptime T: type, int: T) RocStr {
+    // determine maximum size for this T
+    comptime const size = comptime blk: {
+        // the string representation of the minimum i128 value uses at most 40 characters
+        var buf: [40]u8 = undefined;
+        var result = std.fmt.bufPrint(&buf, "{}", .{std.math.minInt(T)}) catch unreachable;
+        break :blk result.len;
+    };
+
+    var buf: [size]u8 = undefined;
+    const result = std.fmt.bufPrint(&buf, "{}", .{int}) catch unreachable;
+
+    return RocStr.init(&buf, result.len);
+}
+
 // Str.split
 
-pub fn strSplitInPlace(
+pub fn strSplitInPlace(array: [*]RocStr, array_len: usize, string: RocStr, delimiter: RocStr) callconv(.C) void {
-    array: [*]RocStr,
-    array_len: usize,
-    str_bytes: [*]const u8,
-    str_len: usize,
-    delimiter_bytes_ptrs: [*]const u8,
-    delimiter_len: usize
-) callconv(.C) void {
     var ret_array_index: usize = 0;
     var sliceStart_index: usize = 0;
     var str_index: usize = 0;
 
+    const str_bytes = string.asU8ptr();
+    const str_len = string.len();
+
+    const delimiter_bytes_ptrs = delimiter.asU8ptr();
+    const delimiter_len = delimiter.len();
+
     if (str_len > delimiter_len) {
         const end_index: usize = str_len - delimiter_len + 1;
         while (str_index <= end_index) {
@@ -247,50 +296,39 @@ pub fn strSplitInPlace(
 
 test "strSplitInPlace: no delimiter" {
     // Str.split "abc" "!" == [ "abc" ]
+    const str_arr = "abc";
+    const str = RocStr.init(str_arr, str_arr.len);
 
-    var str: [3]u8 = "abc".*;
+    const delimiter_arr = "!";
-    const str_ptr: [*]const u8 = &str;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-
-    var delimiter: [1]u8 = "!".*;
-    const delimiter_ptr: [*]const u8 = &delimiter;
 
     var array: [1]RocStr = undefined;
     const array_ptr: [*]RocStr = &array;
 
-    strSplitInPlace(
+    strSplitInPlace(array_ptr, 1, str, delimiter);
-        array_ptr,
-        1,
-        str_ptr,
-        3,
-        delimiter_ptr,
-        1
-    );
 
     var expected = [1]RocStr{
-        RocStr.init(str_ptr, 3),
+        str,
     };
 
     expectEqual(array.len, expected.len);
-    // TODO: fix those tests
+    expect(array[0].eq(expected[0]));
-    //expect(array[0].eq(expected[0]));
 
     for (array) |roc_str| {
-        roc_str.drop();
+        roc_str.deinit();
     }
 
     for (expected) |roc_str| {
-        roc_str.drop();
+        roc_str.deinit();
     }
 }
 
 test "strSplitInPlace: empty end" {
-    const str_len: usize = 50;
+    const str_arr = "1---- ---- ---- ---- ----2---- ---- ---- ---- ----";
-    var str: [str_len]u8 = "1---- ---- ---- ---- ----2---- ---- ---- ---- ----".*;
+    const str = RocStr.init(str_arr, str_arr.len);
-    const str_ptr: [*]u8 = &str;
 
-    const delimiter_len = 24;
+    const delimiter_arr = "---- ---- ---- ---- ----";
-    const delimiter: [delimiter_len:0]u8 = "---- ---- ---- ---- ----".*;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-    const delimiter_ptr: [*]const u8 = &delimiter;
 
     const array_len: usize = 3;
     var array: [array_len]RocStr = [_]RocStr{
@@ -300,43 +338,27 @@ test "strSplitInPlace: empty end" {
     };
     const array_ptr: [*]RocStr = &array;
 
-        strSplitInPlace(
+    strSplitInPlace(array_ptr, array_len, str, delimiter);
-            array_ptr,
-            array_len,
-            str_ptr,
-            str_len,
-            delimiter_ptr,
-            delimiter_len
-        );
 
-        const first_expected_str_len: usize = 1;
+    const one = RocStr.init("1", 1);
-        var first_expected_str: [first_expected_str_len]u8 = "1".*;
+    const two = RocStr.init("2", 1);
-        const first_expected_str_ptr: [*]u8 = &first_expected_str;
-        var firstExpectedRocStr = RocStr.init(first_expected_str_ptr, first_expected_str_len);
 
-        const second_expected_str_len: usize = 1;
+    var expected = [3]RocStr{
-        var second_expected_str: [second_expected_str_len]u8 = "2".*;
+        one, two, RocStr.empty(),
-        const second_expected_str_ptr: [*]u8 = &second_expected_str;
+    };
-        var secondExpectedRocStr = RocStr.init(second_expected_str_ptr, second_expected_str_len);
 
-        // TODO: fix those tests
+    expectEqual(array.len, expected.len);
-        // expectEqual(array.len, 3);
+    expect(array[0].eq(expected[0]));
-        // expectEqual(array[0].str_len, 1);
+    expect(array[1].eq(expected[1]));
-        // expect(array[0].eq(firstExpectedRocStr));
+    expect(array[2].eq(expected[2]));
-        // expect(array[1].eq(secondExpectedRocStr));
-        // expectEqual(array[2].str_len, 0);
 }
 
 test "strSplitInPlace: delimiter on sides" {
-    // Str.split "tttghittt" "ttt" == [ "", "ghi", "" ]
+    const str_arr = "tttghittt";
+    const str = RocStr.init(str_arr, str_arr.len);
 
-    const str_len: usize = 9;
+    const delimiter_arr = "ttt";
-    var str: [str_len]u8 = "tttghittt".*;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-    const str_ptr: [*]u8 = &str;
-
-    const delimiter_len = 3;
-    var delimiter: [delimiter_len]u8 = "ttt".*;
-    const delimiter_ptr: [*]u8 = &delimiter;
 
     const array_len: usize = 3;
     var array: [array_len]RocStr = [_]RocStr{
@@ -345,93 +367,60 @@ test "strSplitInPlace: delimiter on sides" {
         undefined,
     };
     const array_ptr: [*]RocStr = &array;
+    strSplitInPlace(array_ptr, array_len, str, delimiter);
 
-    strSplitInPlace(
+    const ghi_arr = "ghi";
-        array_ptr,
+    const ghi = RocStr.init(ghi_arr, ghi_arr.len);
-        array_len,
-        str_ptr,
-        str_len,
-        delimiter_ptr,
-        delimiter_len
-    );
 
-    const expected_str_len: usize = 3;
+    var expected = [3]RocStr{
-    var expected_str: [expected_str_len]u8 = "ghi".*;
+        RocStr.empty(), ghi, RocStr.empty(),
-    const expected_str_ptr: [*]const u8 = &expected_str;
+    };
-    var expectedRocStr = RocStr.init(expected_str_ptr, expected_str_len);
 
-    // TODO: fix those tests
+    expectEqual(array.len, expected.len);
-    // expectEqual(array.len, 3);
+    expect(array[0].eq(expected[0]));
-    // expectEqual(array[0].str_len, 0);
+    expect(array[1].eq(expected[1]));
-    // expect(array[1].eq(expectedRocStr));
+    expect(array[2].eq(expected[2]));
-    // expectEqual(array[2].str_len, 0);
 }
 
 test "strSplitInPlace: three pieces" {
     // Str.split "a!b!c" "!" == [ "a", "b", "c" ]
+    const str_arr = "a!b!c";
+    const str = RocStr.init(str_arr, str_arr.len);
 
-    const str_len: usize = 5;
+    const delimiter_arr = "!";
-    var str: [str_len]u8 = "a!b!c".*;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-    const str_ptr: [*]u8 = &str;
-
-    const delimiter_len = 1;
-    var delimiter: [delimiter_len]u8 = "!".*;
-    const delimiter_ptr: [*]u8 = &delimiter;
 
     const array_len: usize = 3;
     var array: [array_len]RocStr = undefined;
     const array_ptr: [*]RocStr = &array;
 
-    strSplitInPlace(
+    strSplitInPlace(array_ptr, array_len, str, delimiter);
-        array_ptr,
-        array_len,
-        str_ptr,
-        str_len,
-        delimiter_ptr,
-        delimiter_len
-    );
 
-    var a: [1]u8 = "a".*;
+    const a = RocStr.init("a", 1);
-    const a_ptr: [*]u8 = &a;
+    const b = RocStr.init("b", 1);
-
+    const c = RocStr.init("c", 1);
-    var b: [1]u8 = "b".*;
-    const b_ptr: [*]u8 = &b;
-
-    var c: [1]u8 = "c".*;
-    const c_ptr: [*]u8 = &c;
 
     var expected_array = [array_len]RocStr{
-        RocStr{
+        a, b, c,
-            .str_bytes = a_ptr,
-            .str_len = 1,
-        },
-        RocStr{
-            .str_bytes = b_ptr,
-            .str_len = 1,
-        },
-        RocStr{
-            .str_bytes = c_ptr,
-            .str_len = 1,
-        }
     };
 
-    // TODO: fix those tests
+    expectEqual(expected_array.len, array.len);
-    // expectEqual(expected_array.len, array.len);
+    expect(array[0].eq(expected_array[0]));
-    // expect(array[0].eq(expected_array[0]));
+    expect(array[1].eq(expected_array[1]));
-    // expect(array[1].eq(expected_array[1]));
+    expect(array[2].eq(expected_array[2]));
-    // expect(array[2].eq(expected_array[2]));
 }
 
 // This is used for `Str.split : Str, Str -> Array Str
 // It is used to count how many segments the input `_str`
 // needs to be broken into, so that we can allocate a array
 // of that size. It always returns at least 1.
-pub fn countSegments(
+pub fn countSegments(string: RocStr, delimiter: RocStr) callconv(.C) usize {
-    str_bytes: [*]u8,
+    const str_bytes = string.asU8ptr();
-    str_len: usize,
+    const str_len = string.len();
-    delimiter_bytes_ptrs: [*]u8,
+
-    delimiter_len: usize
+    const delimiter_bytes_ptrs = delimiter.asU8ptr();
-) callconv(.C) usize {
+    const delimiter_len = delimiter.len();
+
     var count: usize = 1;
 
     if (str_len > delimiter_len) {
@@ -469,21 +458,13 @@ pub fn countSegments(
 test "countSegments: long delimiter" {
     // Str.split "str" "delimiter" == [ "str" ]
     // 1 segment
+    const str_arr = "str";
+    const str = RocStr.init(str_arr, str_arr.len);
 
-    const str_len: usize = 3;
+    const delimiter_arr = "delimiter";
-    var str: [str_len]u8 = "str".*;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-    const str_ptr: [*]u8 = &str;
 
-    const delimiter_len = 9;
+    const segments_count = countSegments(str, delimiter);
-    var delimiter: [delimiter_len]u8 = "delimiter".*;
-    const delimiter_ptr: [*]u8 = &delimiter;
-
-    const segments_count = countSegments(
-        str_ptr,
-        str_len,
-        delimiter_ptr,
-        delimiter_len
-    );
 
     expectEqual(segments_count, 1);
 }
@@ -491,21 +472,13 @@ test "countSegments: long delimiter" {
 test "countSegments: delimiter at start" {
     // Str.split "hello there" "hello" == [ "", " there" ]
     // 2 segments
+    const str_arr = "hello there";
+    const str = RocStr.init(str_arr, str_arr.len);
 
-    const str_len: usize = 11;
+    const delimiter_arr = "hello";
-    var str: [str_len]u8 = "hello there".*;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-    const str_ptr: [*]u8 = &str;
 
-    const delimiter_len = 5;
+    const segments_count = countSegments(str, delimiter);
-    var delimiter: [delimiter_len]u8 = "hello".*;
-    const delimiter_ptr: [*]u8 = &delimiter;
-
-    const segments_count = countSegments(
-        str_ptr,
-        str_len,
-        delimiter_ptr,
-        delimiter_len
-    );
 
     expectEqual(segments_count, 2);
 }
@@ -513,21 +486,13 @@ test "countSegments: delimiter at start" {
 test "countSegments: delimiter interspered" {
     // Str.split "a!b!c" "!" == [ "a", "b", "c" ]
     // 3 segments
+    const str_arr = "a!b!c";
+    const str = RocStr.init(str_arr, str_arr.len);
 
-    const str_len: usize = 5;
+    const delimiter_arr = "!";
-    var str: [str_len]u8 = "a!b!c".*;
+    const delimiter = RocStr.init(delimiter_arr, delimiter_arr.len);
-    const str_ptr: [*]u8 = &str;
 
-    const delimiter_len = 1;
+    const segments_count = countSegments(str, delimiter);
-    var delimiter: [delimiter_len]u8 = "!".*;
-    const delimiter_ptr: [*]u8 = &delimiter;
-
-    const segments_count = countSegments(
-        str_ptr,
-        str_len,
-        delimiter_ptr,
-        delimiter_len
-    );
 
     expectEqual(segments_count, 3);
 }
@@ -535,7 +500,14 @@ test "countSegments: delimiter interspered" {
 // Str.countGraphemeClusters
 const grapheme = @import("helpers/grapheme.zig");
 
-pub fn countGraphemeClusters(bytes_ptr: [*]u8, bytes_len: usize)  callconv(.C) usize {
+pub fn countGraphemeClusters(string: RocStr) callconv(.C) usize {
+    if (string.isEmpty()) {
+        return 0;
+    }
+
+    const bytes_len = string.len();
+    const bytes_ptr = string.asU8ptr();
+
     var bytes = bytes_ptr[0..bytes_len];
     var iter = (unicode.Utf8View.init(bytes) catch unreachable).iterator();
 
@@ -545,11 +517,7 @@ pub fn countGraphemeClusters(bytes_ptr: [*]u8, bytes_len: usize)  callconv(.C) u
     var opt_last_codepoint: ?u21 = null;
     while (iter.nextCodepoint()) |cur_codepoint| {
         if (opt_last_codepoint) |last_codepoint| {
-            var did_break = grapheme.isGraphemeBreak(
+            var did_break = grapheme.isGraphemeBreak(last_codepoint, cur_codepoint, grapheme_break_state_ptr);
-                last_codepoint,
-                cur_codepoint,
-                grapheme_break_state_ptr
-            );
             if (did_break) {
                 count += 1;
                 grapheme_break_state = null;
@@ -567,63 +535,57 @@ pub fn countGraphemeClusters(bytes_ptr: [*]u8, bytes_len: usize)  callconv(.C) u
     return count;
 }
 
+fn rocStrFromLiteral(bytes_arr: *const []u8) RocStr {}
+
 test "countGraphemeClusters: empty string" {
-    var bytes_arr = "".*;
+    const count = countGraphemeClusters(RocStr.empty());
-    var bytes_len = bytes_arr.len;
-    var bytes_ptr: [*]u8 = &bytes_arr;
-    var count = countGraphemeClusters(bytes_ptr, bytes_len);
     expectEqual(count, 0);
 }
 
 test "countGraphemeClusters: ascii characters" {
-    var bytes_arr = "abcd".*;
+    const bytes_arr = "abcd";
-    var bytes_len = bytes_arr.len;
+    const bytes_len = bytes_arr.len;
-    var bytes_ptr: [*]u8 = &bytes_arr;
+    const count = countGraphemeClusters(RocStr.init(bytes_arr, bytes_len));
-    var count = countGraphemeClusters(bytes_ptr, bytes_len);
     expectEqual(count, 4);
 }
 
 test "countGraphemeClusters: utf8 characters" {
-    var bytes_arr = "ãxā".*;
+    const bytes_arr = "ãxā";
-    var bytes_len = bytes_arr.len;
+    const bytes_len = bytes_arr.len;
-    var bytes_ptr: [*]u8 = &bytes_arr;
+    const count = countGraphemeClusters(RocStr.init(bytes_arr, bytes_len));
-    var count = countGraphemeClusters(bytes_ptr, bytes_len);
     expectEqual(count, 3);
 }
 
 test "countGraphemeClusters: emojis" {
-    var bytes_arr = "🤔🤔🤔".*;
+    const bytes_arr = "🤔🤔🤔";
-    var bytes_len = bytes_arr.len;
+    const bytes_len = bytes_arr.len;
-    var bytes_ptr: [*]u8 = &bytes_arr;
+    const count = countGraphemeClusters(RocStr.init(bytes_arr, bytes_len));
-    var count = countGraphemeClusters(bytes_ptr, bytes_len);
     expectEqual(count, 3);
 }
 
 test "countGraphemeClusters: emojis and ut8 characters" {
-    var bytes_arr = "🤔å🤔¥🤔ç".*;
+    const bytes_arr = "🤔å🤔¥🤔ç";
-    var bytes_len = bytes_arr.len;
+    const bytes_len = bytes_arr.len;
-    var bytes_ptr: [*]u8 = &bytes_arr;
+    const count = countGraphemeClusters(RocStr.init(bytes_arr, bytes_len));
-    var count = countGraphemeClusters(bytes_ptr, bytes_len);
     expectEqual(count, 6);
 }
 
 test "countGraphemeClusters: emojis, ut8, and ascii characters" {
-    var bytes_arr = "6🤔å🤔e¥🤔çpp".*;
+    const bytes_arr = "6🤔å🤔e¥🤔çpp";
-    var bytes_len = bytes_arr.len;
+    const bytes_len = bytes_arr.len;
-    var bytes_ptr: [*]u8 = &bytes_arr;
+    const count = countGraphemeClusters(RocStr.init(bytes_arr, bytes_len));
-    var count = countGraphemeClusters(bytes_ptr, bytes_len);
     expectEqual(count, 10);
 }
 
-
 // Str.startsWith
 
-pub fn startsWith(
+pub fn startsWith(string: RocStr, prefix: RocStr) callconv(.C) bool {
-    bytes_ptr: [*]u8,
+    const bytes_len = string.len();
-    bytes_len: usize,
+    const bytes_ptr = string.asU8ptr();
-    prefix_ptr: [*]u8,
+
-    prefix_len: usize
+    const prefix_len = prefix.len();
-) callconv(.C) bool {
+    const prefix_ptr = prefix.asU8ptr();
+
     if (prefix_len > bytes_len) {
         return false;
     }
@@ -639,23 +601,211 @@ pub fn startsWith(
     return true;
 }
 
+test "startsWith: foo starts with fo" {
+    const foo = RocStr.init("foo", 3);
+    const fo = RocStr.init("fo", 2);
+    expect(startsWith(foo, fo));
+}
 
 test "startsWith: 123456789123456789 starts with 123456789123456789" {
-    const str_len: usize = 18;
+    const str = RocStr.init("123456789123456789", 18);
-    var str: [str_len]u8 = "123456789123456789".*;
+    expect(startsWith(str, str));
-    const str_ptr: [*]u8 = &str;
-
-    expect(startsWith(str_ptr, str_len, str_ptr, str_len));
 }
 
 test "startsWith: 12345678912345678910 starts with 123456789123456789" {
-    const str_len: usize = 20;
+    const str = RocStr.init("12345678912345678910", 20);
-    var str: [str_len]u8 = "12345678912345678910".*;
+    const prefix = RocStr.init("123456789123456789", 18);
-    const str_ptr: [*]u8 = &str;
 
-    const prefix_len: usize = 18;
+    expect(startsWith(str, prefix));
-    var prefix: [prefix_len]u8 = "123456789123456789".*;
+}
-    const prefix_ptr: [*]u8 = &str;
+
-
+// Str.endsWith
-    expect(startsWith(str_ptr, str_len, prefix_ptr, prefix_len));
+
+pub fn endsWith(string: RocStr, suffix: RocStr) callconv(.C) bool {
+    const bytes_len = string.len();
+    const bytes_ptr = string.asU8ptr();
+
+    const suffix_len = suffix.len();
+    const suffix_ptr = suffix.asU8ptr();
+
+    if (suffix_len > bytes_len) {
+        return false;
+    }
+
+    const offset: usize = bytes_len - suffix_len;
+    var i: usize = 0;
+    while (i < suffix_len) {
+        if (bytes_ptr[i + offset] != suffix_ptr[i]) {
+            return false;
+        }
+        i += 1;
+    }
+    return true;
+}
+
+test "endsWith: foo ends with oo" {
+    const foo = RocStr.init("foo", 3);
+    const oo = RocStr.init("oo", 2);
+    expect(endsWith(foo, oo));
+}
+
+test "endsWith: 123456789123456789 ends with 123456789123456789" {
+    const str = RocStr.init("123456789123456789", 18);
+    expect(endsWith(str, str));
+}
+
+test "endsWith: 12345678912345678910 ends with 345678912345678910" {
+    const str = RocStr.init("12345678912345678910", 20);
+    const suffix = RocStr.init("345678912345678910", 18);
+
+    expect(endsWith(str, suffix));
+}
+
+test "endsWith: hello world ends with world" {
+    const str = RocStr.init("hello world", 11);
+    const suffix = RocStr.init("world", 5);
+
+    expect(endsWith(str, suffix));
+}
+
+// Str.concat
+
+test "RocStr.concat: small concat small" {
+    const str1_len = 3;
+    var str1: [str1_len]u8 = "foo".*;
+    const str1_ptr: [*]u8 = &str1;
+    var roc_str1 = RocStr.init(str1_ptr, str1_len);
+
+    const str2_len = 3;
+    var str2: [str2_len]u8 = "abc".*;
+    const str2_ptr: [*]u8 = &str2;
+    var roc_str2 = RocStr.init(str2_ptr, str2_len);
+
+    const str3_len = 6;
+    var str3: [str3_len]u8 = "fooabc".*;
+    const str3_ptr: [*]u8 = &str3;
+    var roc_str3 = RocStr.init(str3_ptr, str3_len);
+
+    const result = strConcat(8, InPlace.Clone, roc_str1, roc_str2);
+
+    expect(roc_str3.eq(result));
+
+    roc_str1.deinit();
+    roc_str2.deinit();
+    roc_str3.deinit();
+    result.deinit();
+}
+
+pub fn strConcat(ptr_size: u32, result_in_place: InPlace, arg1: RocStr, arg2: RocStr) callconv(.C) RocStr {
+    return switch (ptr_size) {
+        4 => strConcatHelp(i32, result_in_place, arg1, arg2),
+        8 => strConcatHelp(i64, result_in_place, arg1, arg2),
+        else => unreachable,
+    };
+}
+
+fn strConcatHelp(comptime T: type, result_in_place: InPlace, arg1: RocStr, arg2: RocStr) RocStr {
+    if (arg1.isEmpty()) {
+        return cloneStr(T, result_in_place, arg2);
+    } else if (arg2.isEmpty()) {
+        return cloneStr(T, result_in_place, arg1);
+    } else {
+        const combined_length = arg1.len() + arg2.len();
+
+        const small_str_bytes = 2 * @sizeOf(T);
+        const result_is_big = combined_length >= small_str_bytes;
+
+        if (result_is_big) {
+            var result = allocateStr(T, result_in_place, combined_length);
+
+            {
+                const old_if_small = &@bitCast([16]u8, arg1);
+                const old_if_big = @ptrCast([*]u8, arg1.str_bytes);
+                const old_bytes = if (arg1.isSmallStr()) old_if_small else old_if_big;
+
+                const new_bytes: [*]u8 = @ptrCast([*]u8, result.str_bytes);
+
+                @memcpy(new_bytes, old_bytes, arg1.len());
+            }
+
+            {
+                const old_if_small = &@bitCast([16]u8, arg2);
+                const old_if_big = @ptrCast([*]u8, arg2.str_bytes);
+                const old_bytes = if (arg2.isSmallStr()) old_if_small else old_if_big;
+
+                const new_bytes = @ptrCast([*]u8, result.str_bytes) + arg1.len();
+
+                @memcpy(new_bytes, old_bytes, arg2.len());
+            }
+
+            return result;
+        } else {
+            var result = [16]u8{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
+
+            // if the result is small, then for sure arg1 and arg2 are also small
+
+            {
+                var old_bytes: [*]u8 = @ptrCast([*]u8, &@bitCast([16]u8, arg1));
+                var new_bytes: [*]u8 = @ptrCast([*]u8, &result);
+
+                @memcpy(new_bytes, old_bytes, arg1.len());
+            }
+
+            {
+                var old_bytes: [*]u8 = @ptrCast([*]u8, &@bitCast([16]u8, arg2));
+                var new_bytes = @ptrCast([*]u8, &result) + arg1.len();
+
+                @memcpy(new_bytes, old_bytes, arg2.len());
+            }
+
+            const mask: u8 = 0b1000_0000;
+            const final_byte = @truncate(u8, combined_length) | mask;
+
+            result[small_str_bytes - 1] = final_byte;
+
+            return @bitCast(RocStr, result);
+        }
+
+        return result;
+    }
+}
+
+const InPlace = packed enum(u8) {
+    InPlace,
+    Clone,
+};
+
+fn cloneStr(comptime T: type, in_place: InPlace, str: RocStr) RocStr {
+    if (str.isSmallStr() or str.isEmpty()) {
+        // just return the bytes
+        return str;
+    } else {
+        var new_str = allocateStr(T, in_place, str.str_len);
+
+        var old_bytes: [*]u8 = @ptrCast([*]u8, str.str_bytes);
+        var new_bytes: [*]u8 = @ptrCast([*]u8, new_str.str_bytes);
+
+        @memcpy(new_bytes, old_bytes, str.str_len);
+
+        return new_str;
+    }
+}
+
+fn allocateStr(comptime T: type, in_place: InPlace, number_of_chars: u64) RocStr {
+    const length = @sizeOf(T) + number_of_chars;
+    var new_bytes: [*]T = @ptrCast([*]T, @alignCast(@alignOf(T), malloc(length)));
+
+    if (in_place == InPlace.InPlace) {
+        new_bytes[0] = @intCast(T, number_of_chars);
+    } else {
+        new_bytes[0] = std.math.minInt(T);
+    }
+
+    var first_element = @ptrCast([*]align(@alignOf(T)) u8, new_bytes);
+    first_element += @sizeOf(usize);
+
+    return RocStr{
+        .str_bytes = first_element,
+        .str_len = number_of_chars,
+    };
 }

compiler/builtins/src/bitcode.rs

@@ -24,6 +24,10 @@ pub const NUM_IS_FINITE: &str = "roc_builtins.num.is_finite";
 pub const NUM_POW_INT: &str = "roc_builtins.num.pow_int";
 
 pub const STR_COUNT_SEGMENTS: &str = "roc_builtins.str.count_segments";
+pub const STR_CONCAT: &str = "roc_builtins.str.concat";
 pub const STR_STR_SPLIT_IN_PLACE: &str = "roc_builtins.str.str_split_in_place";
 pub const STR_COUNT_GRAPEHEME_CLUSTERS: &str = "roc_builtins.str.count_grapheme_clusters";
 pub const STR_STARTS_WITH: &str = "roc_builtins.str.starts_with";
+pub const STR_ENDS_WITH: &str = "roc_builtins.str.ends_with";
+pub const STR_NUMBER_OF_BYTES: &str = "roc_builtins.str.number_of_bytes";
+pub const STR_FROM_INT: &str = "roc_builtins.str.from_int";

compiler/builtins/src/std.rs

@@ -417,12 +417,24 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         top_level_function(vec![str_type(), str_type()], Box::new(bool_type())),
     );
 
+    // endsWith : Str, Str -> Bool
+    add_type(
+        Symbol::STR_ENDS_WITH,
+        top_level_function(vec![str_type(), str_type()], Box::new(bool_type())),
+    );
+
     // countGraphemes : Str -> Int
     add_type(
         Symbol::STR_COUNT_GRAPHEMES,
         top_level_function(vec![str_type()], Box::new(int_type())),
     );
 
+    // fromInt : Int -> Str
+    add_type(
+        Symbol::STR_FROM_INT,
+        top_level_function(vec![int_type()], Box::new(str_type())),
+    );
+
     // List module
 
     // get : List elem, Int -> Result elem [ OutOfBounds ]*

compiler/builtins/src/unique.rs

@@ -1096,12 +1096,24 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         unique_function(vec![str_type(star1), str_type(star2)], bool_type(star3))
     });
 
+    // Str.endsWith : Attr * Str, Attr * Str -> Attr * Bool
+    add_type(Symbol::STR_ENDS_WITH, {
+        let_tvars! { star1, star2, star3 };
+        unique_function(vec![str_type(star1), str_type(star2)], bool_type(star3))
+    });
+
     // Str.countGraphemes : Attr * Str, -> Attr * Int
     add_type(Symbol::STR_COUNT_GRAPHEMES, {
         let_tvars! { star1, star2 };
         unique_function(vec![str_type(star1)], int_type(star2))
     });
 
+    // fromInt : Attr * Int -> Attr * Str
+    add_type(Symbol::STR_FROM_INT, {
+        let_tvars! { star1, star2 };
+        unique_function(vec![int_type(star1)], str_type(star2))
+    });
+
     // Result module
 
     // map : Attr * (Result (Attr a e))

compiler/can/src/builtins.rs

@@ -54,7 +54,9 @@ pub fn builtin_defs(var_store: &mut VarStore) -> MutMap<Symbol, Def> {
         Symbol::STR_SPLIT => str_split,
         Symbol::STR_IS_EMPTY => str_is_empty,
         Symbol::STR_STARTS_WITH => str_starts_with,
+        Symbol::STR_ENDS_WITH => str_ends_with,
         Symbol::STR_COUNT_GRAPHEMES => str_count_graphemes,
+        Symbol::STR_FROM_INT => str_from_int,
         Symbol::LIST_LEN => list_len,
         Symbol::LIST_GET => list_get,
         Symbol::LIST_SET => list_set,
@@ -989,6 +991,26 @@ fn str_starts_with(symbol: Symbol, var_store: &mut VarStore) -> Def {
     )
 }
 
+/// Str.endsWith : Str, Str -> Bool
+fn str_ends_with(symbol: Symbol, var_store: &mut VarStore) -> Def {
+    let str_var = var_store.fresh();
+    let bool_var = var_store.fresh();
+
+    let body = RunLowLevel {
+        op: LowLevel::StrEndsWith,
+        args: vec![(str_var, Var(Symbol::ARG_1)), (str_var, Var(Symbol::ARG_2))],
+        ret_var: bool_var,
+    };
+
+    defn(
+        symbol,
+        vec![(str_var, Symbol::ARG_1), (str_var, Symbol::ARG_2)],
+        var_store,
+        body,
+        bool_var,
+    )
+}
+
 /// Str.countGraphemes : Str -> Int
 fn str_count_graphemes(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let str_var = var_store.fresh();
@@ -1009,6 +1031,26 @@ fn str_count_graphemes(symbol: Symbol, var_store: &mut VarStore) -> Def {
     )
 }
 
+/// Str.fromInt : Int -> Str
+fn str_from_int(symbol: Symbol, var_store: &mut VarStore) -> Def {
+    let int_var = var_store.fresh();
+    let str_var = var_store.fresh();
+
+    let body = RunLowLevel {
+        op: LowLevel::StrFromInt,
+        args: vec![(int_var, Var(Symbol::ARG_1))],
+        ret_var: str_var,
+    };
+
+    defn(
+        symbol,
+        vec![(int_var, Symbol::ARG_1)],
+        var_store,
+        body,
+        str_var,
+    )
+}
+
 /// List.concat : List elem, List elem -> List elem
 fn list_concat(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let list_var = var_store.fresh();

compiler/gen/src/llvm/build.rs

@@ -4,7 +4,8 @@ use crate::llvm::build_list::{
     list_reverse, list_set, list_single, list_sum, list_walk, list_walk_backwards,
 };
 use crate::llvm::build_str::{
-    str_concat, str_count_graphemes, str_len, str_split, str_starts_with, CHAR_LAYOUT,
+    str_concat, str_count_graphemes, str_ends_with, str_from_int, str_number_of_bytes, str_split,
+    str_starts_with, CHAR_LAYOUT,
 };
 use crate::llvm::compare::{build_eq, build_neq};
 use crate::llvm::convert::{
@@ -604,7 +605,9 @@ pub fn build_exp_expr<'a, 'ctx, 'env>(
 
     match expr {
         Literal(literal) => build_exp_literal(env, literal),
-        RunLowLevel(op, symbols) => run_low_level(env, scope, parent, layout, *op, symbols),
+        RunLowLevel(op, symbols) => {
+            run_low_level(env, layout_ids, scope, parent, layout, *op, symbols)
+        }
 
         ForeignCall {
             foreign_symbol,
@@ -1165,12 +1168,10 @@ fn list_literal<'a, 'ctx, 'env>(
     let builder = env.builder;
 
     let len_u64 = elems.len() as u64;
-    let elem_bytes = elem_layout.stack_size(env.ptr_bytes) as u64;
 
     let ptr = {
-        let bytes_len = elem_bytes * len_u64;
         let len_type = env.ptr_int();
-        let len = len_type.const_int(bytes_len, false);
+        let len = len_type.const_int(len_u64, false);
 
         allocate_list(env, inplace, elem_layout, len)
 
@@ -2383,6 +2384,7 @@ fn call_with_args<'a, 'ctx, 'env>(
 }
 
 #[derive(Copy, Clone)]
+#[repr(u8)]
 pub enum InPlace {
     InPlace,
     Clone,
@@ -2409,6 +2411,7 @@ pub static COLD_CALL_CONV: u32 = 9;
 
 fn run_low_level<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
+    layout_ids: &mut LayoutIds<'a>,
     scope: &Scope<'a, 'ctx>,
     parent: FunctionValue<'ctx>,
     layout: &Layout<'a>,
@@ -2424,15 +2427,25 @@ fn run_low_level<'a, 'ctx, 'env>(
 
             let inplace = get_inplace_from_layout(layout);
 
-            str_concat(env, inplace, scope, parent, args[0], args[1])
+            str_concat(env, inplace, scope, args[0], args[1])
         }
         StrStartsWith => {
             // Str.startsWith : Str, Str -> Bool
             debug_assert_eq!(args.len(), 2);
 
-            let inplace = get_inplace_from_layout(layout);
+            str_starts_with(env, scope, args[0], args[1])
+        }
+        StrEndsWith => {
+            // Str.startsWith : Str, Str -> Bool
+            debug_assert_eq!(args.len(), 2);
 
-            str_starts_with(env, inplace, scope, parent, args[0], args[1])
+            str_ends_with(env, scope, args[0], args[1])
+        }
+        StrFromInt => {
+            // Str.fromInt : Int -> Str
+            debug_assert_eq!(args.len(), 1);
+
+            str_from_int(env, scope, args[0])
         }
         StrSplit => {
             // Str.split : Str, Str -> List Str
@@ -2440,14 +2453,13 @@ fn run_low_level<'a, 'ctx, 'env>(
 
             let inplace = get_inplace_from_layout(layout);
 
-            str_split(env, scope, parent, inplace, args[0], args[1])
+            str_split(env, scope, inplace, args[0], args[1])
         }
         StrIsEmpty => {
             // Str.isEmpty : Str -> Str
             debug_assert_eq!(args.len(), 1);
 
-            let wrapper_ptr = ptr_from_symbol(scope, args[0]);
+            let len = str_number_of_bytes(env, scope, args[0]);
-            let len = str_len(env, parent, *wrapper_ptr);
             let is_zero = env.builder.build_int_compare(
                 IntPredicate::EQ,
                 len,
@@ -2460,7 +2472,7 @@ fn run_low_level<'a, 'ctx, 'env>(
             // Str.countGraphemes : Str -> Int
             debug_assert_eq!(args.len(), 1);
 
-            str_count_graphemes(env, scope, parent, args[0])
+            str_count_graphemes(env, scope, args[0])
         }
         ListLen => {
             // List.len : List * -> Int
@@ -2522,7 +2534,16 @@ fn run_low_level<'a, 'ctx, 'env>(
 
             let inplace = get_inplace_from_layout(layout);
 
-            list_map(env, inplace, parent, func, func_layout, list, list_layout)
+            list_map(
+                env,
+                layout_ids,
+                inplace,
+                parent,
+                func,
+                func_layout,
+                list,
+                list_layout,
+            )
         }
         ListKeepIf => {
             // List.keepIf : List elem, (elem -> Bool) -> List elem

compiler/gen/src/llvm/build_list.rs

@@ -3,12 +3,13 @@ use crate::llvm::build::{
 };
 use crate::llvm::compare::build_eq;
 use crate::llvm::convert::{basic_type_from_layout, collection, get_ptr_type};
+use crate::llvm::refcounting::{decrement_refcount_layout, increment_refcount_layout};
 use inkwell::builder::Builder;
 use inkwell::context::Context;
 use inkwell::types::{BasicTypeEnum, PointerType};
 use inkwell::values::{BasicValueEnum, FunctionValue, IntValue, PointerValue, StructValue};
 use inkwell::{AddressSpace, IntPredicate};
-use roc_mono::layout::{Builtin, Layout, MemoryMode};
+use roc_mono::layout::{Builtin, Layout, LayoutIds, MemoryMode};
 
 /// List.single : a -> List a
 pub fn list_single<'a, 'ctx, 'env>(
@@ -1318,33 +1319,47 @@ pub fn list_keep_if_help<'a, 'ctx, 'env>(
 }
 
 /// List.map : List before, (before -> after) -> List after
-pub fn list_map<'a, 'ctx, 'env>(
+macro_rules! list_map_help {
-    env: &Env<'a, 'ctx, 'env>,
+    ($env:expr, $layout_ids:expr, $inplace:expr, $parent:expr, $func:expr, $func_layout:expr, $list:expr, $list_layout:expr, $function_ptr:expr, $function_return_layout: expr, $closure_info:expr) => {{
-    inplace: InPlace,
+        let layout_ids = $layout_ids;
-    parent: FunctionValue<'ctx>,
+        let inplace = $inplace;
-    func: BasicValueEnum<'ctx>,
+        let parent = $parent;
-    func_layout: &Layout<'a>,
+        let func = $func;
-    list: BasicValueEnum<'ctx>,
+        let func_layout = $func_layout;
-    list_layout: &Layout<'a>,
+        let list = $list;
-) -> BasicValueEnum<'ctx> {
+        let list_layout = $list_layout;
-    match (func, func_layout) {
+        let function_ptr = $function_ptr;
-        (BasicValueEnum::PointerValue(func_ptr), Layout::FunctionPointer(_, ret_elem_layout)) => {
+        let function_return_layout = $function_return_layout;
+        let closure_info : Option<(&Layout, BasicValueEnum)> = $closure_info;
+
+
         let non_empty_fn = |elem_layout: &Layout<'a>,
                             len: IntValue<'ctx>,
                             list_wrapper: StructValue<'ctx>| {
-                let ctx = env.context;
+            let ctx = $env.context;
-                let builder = env.builder;
+            let builder = $env.builder;
 
-                let ret_list_ptr = allocate_list(env, inplace, ret_elem_layout, len);
+            let ret_list_ptr = allocate_list($env, inplace, function_return_layout, len);
 
-                let elem_type = basic_type_from_layout(env.arena, ctx, elem_layout, env.ptr_bytes);
+            let elem_type = basic_type_from_layout($env.arena, ctx, elem_layout, $env.ptr_bytes);
             let ptr_type = get_ptr_type(&elem_type, AddressSpace::Generic);
 
             let list_ptr = load_list_ptr(builder, list_wrapper, ptr_type);
 
             let list_loop = |index, before_elem| {
-                    let call_site_value =
+                increment_refcount_layout($env, parent, layout_ids, before_elem, elem_layout);
-                        builder.build_call(func_ptr, env.arena.alloc([before_elem]), "map_func");
+
+                let arguments = match closure_info {
+                    Some((closure_data_layout, closure_data)) => {
+                        increment_refcount_layout( $env, parent, layout_ids, closure_data, closure_data_layout);
+
+                        bumpalo::vec![in $env.arena; before_elem, closure_data]
+                    }
+                    None => bumpalo::vec![in $env.arena; before_elem],
+                };
+
+
+                let call_site_value = builder.build_call(function_ptr, &arguments, "map_func");
 
                 // set the calling convention explicitly for this call
                 call_site_value.set_call_convention(crate::llvm::build::FAST_CALL_CONV);
@@ -1365,10 +1380,81 @@ pub fn list_map<'a, 'ctx, 'env>(
 
             incrementing_elem_loop(builder, ctx, parent, list_ptr, len, "#index", list_loop);
 
-                store_list(env, ret_list_ptr, len)
+            let result = store_list($env, ret_list_ptr, len);
+
+            // decrement the input list and function (if it's a closure)
+            decrement_refcount_layout($env, parent, layout_ids, list, list_layout);
+            decrement_refcount_layout($env, parent, layout_ids, func, func_layout);
+
+            if let Some((closure_data_layout, closure_data))  = closure_info  {
+                decrement_refcount_layout( $env, parent, layout_ids, closure_data, closure_data_layout);
+            }
+
+            result
         };
 
-            if_list_is_not_empty(env, parent, non_empty_fn, list, list_layout, "List.map")
+        if_list_is_not_empty($env, parent, non_empty_fn, list, list_layout, "List.map")
+    }};
+}
+
+/// List.map : List before, (before -> after) -> List after
+#[allow(clippy::too_many_arguments)]
+pub fn list_map<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    layout_ids: &mut LayoutIds<'a>,
+    inplace: InPlace,
+    parent: FunctionValue<'ctx>,
+    func: BasicValueEnum<'ctx>,
+    func_layout: &Layout<'a>,
+    list: BasicValueEnum<'ctx>,
+    list_layout: &Layout<'a>,
+) -> BasicValueEnum<'ctx> {
+    match (func, func_layout) {
+        (BasicValueEnum::PointerValue(func_ptr), Layout::FunctionPointer(_, ret_elem_layout)) => {
+            list_map_help!(
+                env,
+                layout_ids,
+                inplace,
+                parent,
+                func,
+                func_layout,
+                list,
+                list_layout,
+                func_ptr,
+                ret_elem_layout,
+                None
+            )
+        }
+        (
+            BasicValueEnum::StructValue(ptr_and_data),
+            Layout::Closure(_, closure_layout, ret_elem_layout),
+        ) => {
+            let builder = env.builder;
+
+            let func_ptr = builder
+                .build_extract_value(ptr_and_data, 0, "function_ptr")
+                .unwrap()
+                .into_pointer_value();
+
+            let closure_data = builder
+                .build_extract_value(ptr_and_data, 1, "closure_data")
+                .unwrap();
+
+            let closure_data_layout = closure_layout.as_block_of_memory_layout();
+
+            list_map_help!(
+                env,
+                layout_ids,
+                inplace,
+                parent,
+                func,
+                func_layout,
+                list,
+                list_layout,
+                func_ptr,
+                ret_elem_layout,
+                Some((&closure_data_layout, closure_data))
+            )
         }
         _ => {
             unreachable!(
@@ -1989,7 +2075,6 @@ pub fn allocate_list<'a, 'ctx, 'env>(
     let len_type = env.ptr_int();
     let elem_bytes = elem_layout.stack_size(env.ptr_bytes) as u64;
     let bytes_per_element = len_type.const_int(elem_bytes, false);
-
     let number_of_data_bytes = builder.build_int_mul(bytes_per_element, length, "data_length");
 
     let rc1 = match inplace {

compiler/gen/src/llvm/build_str.rs

@@ -1,64 +1,41 @@
 use crate::llvm::build::{
     call_bitcode_fn, call_void_bitcode_fn, ptr_from_symbol, Env, InPlace, Scope,
 };
-use crate::llvm::build_list::{
+use crate::llvm::build_list::{allocate_list, store_list};
-    allocate_list, build_basic_phi2, empty_list, incrementing_elem_loop, load_list_ptr, store_list,
-};
 use crate::llvm::convert::collection;
-use inkwell::builder::Builder;
 use inkwell::types::BasicTypeEnum;
-use inkwell::values::{BasicValueEnum, FunctionValue, IntValue, PointerValue, StructValue};
+use inkwell::values::{BasicValueEnum, IntValue, StructValue};
-use inkwell::{AddressSpace, IntPredicate};
+use inkwell::AddressSpace;
 use roc_builtins::bitcode;
 use roc_module::symbol::Symbol;
 use roc_mono::layout::{Builtin, Layout};
 
+use super::build::load_symbol;
+
 pub static CHAR_LAYOUT: Layout = Layout::Builtin(Builtin::Int8);
 
 /// Str.split : Str, Str -> List Str
 pub fn str_split<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     scope: &Scope<'a, 'ctx>,
-    parent: FunctionValue<'ctx>,
     inplace: InPlace,
     str_symbol: Symbol,
     delimiter_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
     let builder = env.builder;
-    let ctx = env.context;
 
-    let str_ptr = ptr_from_symbol(scope, str_symbol);
+    let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
-    let delimiter_ptr = ptr_from_symbol(scope, delimiter_symbol);
+    let delim_i128 = str_symbol_to_i128(env, scope, delimiter_symbol);
 
-    let str_wrapper_type = BasicTypeEnum::StructType(collection(ctx, env.ptr_bytes));
-
-    load_str(
-        env,
-        parent,
-        *str_ptr,
-        str_wrapper_type,
-        |str_bytes_ptr, str_len, _str_smallness| {
-            load_str(
-                env,
-                parent,
-                *delimiter_ptr,
-                str_wrapper_type,
-                |delimiter_bytes_ptr, delimiter_len, _delimiter_smallness| {
     let segment_count = call_bitcode_fn(
         env,
-                        &[
+        &[str_i128.into(), delim_i128.into()],
-                            BasicValueEnum::PointerValue(str_bytes_ptr),
-                            BasicValueEnum::IntValue(str_len),
-                            BasicValueEnum::PointerValue(delimiter_bytes_ptr),
-                            BasicValueEnum::IntValue(delimiter_len),
-                        ],
         &bitcode::STR_COUNT_SEGMENTS,
     )
     .into_int_value();
 
     // a pointer to the elements
-                    let ret_list_ptr =
+    let ret_list_ptr = allocate_list(env, inplace, &Layout::Builtin(Builtin::Str), segment_count);
-                        allocate_list(env, inplace, &Layout::Builtin(Builtin::Str), segment_count);
 
     // get the RocStr type defined by zig
     let roc_str_type = env.module.get_struct_type("str.RocStr").unwrap();
@@ -75,19 +52,69 @@ pub fn str_split<'a, 'ctx, 'env>(
         &[
             ret_list_ptr_zig_rocstr,
             BasicValueEnum::IntValue(segment_count),
-                            BasicValueEnum::PointerValue(str_bytes_ptr),
+            str_i128.into(),
-                            BasicValueEnum::IntValue(str_len),
+            delim_i128.into(),
-                            BasicValueEnum::PointerValue(delimiter_bytes_ptr),
-                            BasicValueEnum::IntValue(delimiter_len),
         ],
         &bitcode::STR_STR_SPLIT_IN_PLACE,
     );
 
     store_list(env, ret_list_ptr, segment_count)
-                },
+}
+
+fn str_symbol_to_i128<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    scope: &Scope<'a, 'ctx>,
+    symbol: Symbol,
+) -> IntValue<'ctx> {
+    let str_ptr = ptr_from_symbol(scope, symbol);
+
+    let i128_ptr = env
+        .builder
+        .build_bitcast(
+            *str_ptr,
+            env.context.i128_type().ptr_type(AddressSpace::Generic),
+            "cast",
         )
-        },
+        .into_pointer_value();
+
+    env.builder
+        .build_load(i128_ptr, "load_as_i128")
+        .into_int_value()
+}
+
+fn zig_str_to_struct<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    zig_str: StructValue<'ctx>,
+) -> StructValue<'ctx> {
+    let builder = env.builder;
+
+    // get the RocStr type defined by zig
+    let zig_str_type = env.module.get_struct_type("str.RocStr").unwrap();
+
+    let ret_type = BasicTypeEnum::StructType(collection(env.context, env.ptr_bytes));
+
+    // a roundabout way of casting (LLVM does not accept a standard bitcast)
+    let allocation = builder.build_alloca(zig_str_type, "zig_result");
+
+    builder.build_store(allocation, zig_str);
+
+    let ptr3 = builder
+        .build_bitcast(
+            allocation,
+            env.context.i128_type().ptr_type(AddressSpace::Generic),
+            "cast",
         )
+        .into_pointer_value();
+
+    let ptr4 = builder
+        .build_bitcast(
+            ptr3,
+            ret_type.into_struct_type().ptr_type(AddressSpace::Generic),
+            "cast",
+        )
+        .into_pointer_value();
+
+    builder.build_load(ptr4, "load").into_struct_value()
 }
 
 /// Str.concat : Str, Str -> Str
@@ -95,622 +122,81 @@ pub fn str_concat<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     inplace: InPlace,
     scope: &Scope<'a, 'ctx>,
-    parent: FunctionValue<'ctx>,
+    str1_symbol: Symbol,
-    first_str_symbol: Symbol,
+    str2_symbol: Symbol,
-    second_str_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
-    let builder = env.builder;
+    // swap the arguments; second argument comes before the second in the output string
-    let ctx = env.context;
+    let str1_i128 = str_symbol_to_i128(env, scope, str1_symbol);
+    let str2_i128 = str_symbol_to_i128(env, scope, str2_symbol);
 
-    let second_str_ptr = ptr_from_symbol(scope, second_str_symbol);
+    let zig_result = call_bitcode_fn(
-    let first_str_ptr = ptr_from_symbol(scope, first_str_symbol);
-
-    let ret_type = BasicTypeEnum::StructType(collection(ctx, env.ptr_bytes));
-
-    load_str(
         env,
-        parent,
+        &[
-        *second_str_ptr,
+            env.context
-        ret_type,
+                .i32_type()
-        |second_str_ptr, second_str_len, second_str_smallness| {
+                .const_int(env.ptr_bytes as u64, false)
-            load_str(
+                .into(),
-                env,
+            env.context
-                parent,
-                *first_str_ptr,
-                ret_type,
-                |first_str_ptr, first_str_len, first_str_smallness| {
-                    // first_str_len > 0
-                    // We do this check to avoid allocating memory. If the first input
-                    // str is empty, then we can just return the second str cloned
-                    let first_str_length_comparison = str_is_not_empty(env, first_str_len);
-
-                    let if_first_str_is_empty = || {
-                        // second_str_len > 0
-                        // We do this check to avoid allocating memory. If the second input
-                        // str is empty, then we can just return an empty str
-                        let second_str_length_comparison = str_is_not_empty(env, second_str_len);
-
-                        let if_second_str_is_nonempty = || {
-                            let (new_wrapper, _) = clone_nonempty_str(
-                                env,
-                                inplace,
-                                second_str_smallness,
-                                second_str_len,
-                                second_str_ptr,
-                            );
-
-                            BasicValueEnum::StructValue(new_wrapper)
-                        };
-
-                        let if_second_str_is_empty = || empty_list(env);
-
-                        build_basic_phi2(
-                            env,
-                            parent,
-                            second_str_length_comparison,
-                            if_second_str_is_nonempty,
-                            if_second_str_is_empty,
-                            ret_type,
-                        )
-                    };
-
-                    let if_first_str_is_not_empty = || {
-                        let if_second_str_is_empty = || {
-                            let (new_wrapper, _) = clone_nonempty_str(
-                                env,
-                                inplace,
-                                first_str_smallness,
-                                first_str_len,
-                                first_str_ptr,
-                            );
-
-                            BasicValueEnum::StructValue(new_wrapper)
-                        };
-
-                        // second_str_len > 0
-                        // We do this check to avoid allocating memory. If the second input
-                        // str is empty, then we can just return the first str cloned
-                        let second_str_length_comparison = str_is_not_empty(env, second_str_len);
-
-                        let if_second_str_is_not_empty = || {
-                            let combined_str_len = builder.build_int_add(
-                                first_str_len,
-                                second_str_len,
-                                "add_list_lengths",
-                            );
-
-                            // The combined string is big iff its length is
-                            // greater than or equal to the size in memory
-                            // of a small str (e.g. len >= 16 on 64-bit targets)
-                            let is_big = env.builder.build_int_compare(
-                                IntPredicate::UGE,
-                                combined_str_len,
-                                env.ptr_int().const_int(env.small_str_bytes() as u64, false),
-                                "str_is_big",
-                            );
-
-                            let if_big = || {
-                                let combined_str_ptr =
-                                    allocate_list(env, inplace, &CHAR_LAYOUT, combined_str_len);
-
-                                // TODO replace FIRST_LOOP with a memcpy!
-                                // FIRST LOOP
-                                let first_loop = |first_index, first_str_elem| {
-                                    // The pointer to the element in the combined list
-                                    let combined_str_elem_ptr = unsafe {
-                                        builder.build_in_bounds_gep(
-                                            combined_str_ptr,
-                                            &[first_index],
-                                            "load_index_combined_list",
-                                        )
-                                    };
-
-                                    // Mutate the new array in-place to change the element.
-                                    builder.build_store(combined_str_elem_ptr, first_str_elem);
-                                };
-
-                                let index_name = "#index";
-
-                                let index_alloca = incrementing_elem_loop(
-                                    builder,
-                                    ctx,
-                                    parent,
-                                    first_str_ptr,
-                                    first_str_len,
-                                    index_name,
-                                    first_loop,
-                                );
-
-                                // Reset the index variable to 0
-                                builder
-                                    .build_store(index_alloca, ctx.i64_type().const_int(0, false));
-
-                                // TODO replace SECOND_LOOP with a memcpy!
-                                // SECOND LOOP
-                                let second_loop = |second_index, second_str_elem| {
-                                    // The pointer to the element in the combined str.
-                                    // Note that the pointer does not start at the index
-                                    // 0, it starts at the index of first_str_len. In that
-                                    // sense it is "offset".
-                                    let offset_combined_str_char_ptr = unsafe {
-                                        builder.build_in_bounds_gep(
-                                            combined_str_ptr,
-                                            &[first_str_len],
-                                            "elem",
-                                        )
-                                    };
-
-                                    // The pointer to the char from the second str
-                                    // in the combined list
-                                    let combined_str_char_ptr = unsafe {
-                                        builder.build_in_bounds_gep(
-                                            offset_combined_str_char_ptr,
-                                            &[second_index],
-                                            "load_index_combined_list",
-                                        )
-                                    };
-
-                                    // Mutate the new array in-place to change the element.
-                                    builder.build_store(combined_str_char_ptr, second_str_elem);
-                                };
-
-                                incrementing_elem_loop(
-                                    builder,
-                                    ctx,
-                                    parent,
-                                    second_str_ptr,
-                                    second_str_len,
-                                    index_name,
-                                    second_loop,
-                                );
-
-                                store_list(env, combined_str_ptr, combined_str_len)
-                            };
-
-                            let if_small = || {
-                                let combined_str_ptr = builder.build_array_alloca(
-                                    ctx.i8_type(),
-                                    ctx.i8_type().const_int(env.small_str_bytes() as u64, false),
-                                    "alloca_small_str",
-                                );
-
-                                // TODO replace FIRST_LOOP with a memcpy!
-                                // FIRST LOOP
-                                let first_loop = |first_index, first_str_elem| {
-                                    // The pointer to the element in the combined list
-                                    let combined_str_elem_ptr = unsafe {
-                                        builder.build_in_bounds_gep(
-                                            combined_str_ptr,
-                                            &[first_index],
-                                            "load_index_combined_list",
-                                        )
-                                    };
-
-                                    // Mutate the new array in-place to change the element.
-                                    builder.build_store(combined_str_elem_ptr, first_str_elem);
-                                };
-
-                                let index_name = "#index";
-
-                                let index_alloca = incrementing_elem_loop(
-                                    builder,
-                                    ctx,
-                                    parent,
-                                    first_str_ptr,
-                                    first_str_len,
-                                    index_name,
-                                    first_loop,
-                                );
-
-                                // Reset the index variable to 0
-                                builder
-                                    .build_store(index_alloca, ctx.i64_type().const_int(0, false));
-
-                                // TODO replace SECOND_LOOP with a memcpy!
-                                // SECOND LOOP
-                                let second_loop = |second_index, second_str_elem| {
-                                    // The pointer to the element in the combined str.
-                                    // Note that the pointer does not start at the index
-                                    // 0, it starts at the index of first_str_len. In that
-                                    // sense it is "offset".
-                                    let offset_combined_str_char_ptr = unsafe {
-                                        builder.build_in_bounds_gep(
-                                            combined_str_ptr,
-                                            &[first_str_len],
-                                            "elem",
-                                        )
-                                    };
-
-                                    // The pointer to the char from the second str
-                                    // in the combined list
-                                    let combined_str_char_ptr = unsafe {
-                                        builder.build_in_bounds_gep(
-                                            offset_combined_str_char_ptr,
-                                            &[second_index],
-                                            "load_index_combined_list",
-                                        )
-                                    };
-
-                                    // Mutate the new array in-place to change the element.
-                                    builder.build_store(combined_str_char_ptr, second_str_elem);
-                                };
-
-                                incrementing_elem_loop(
-                                    builder,
-                                    ctx,
-                                    parent,
-                                    second_str_ptr,
-                                    second_str_len,
-                                    index_name,
-                                    second_loop,
-                                );
-
-                                let final_byte = builder.build_int_cast(
-                                    combined_str_len,
-                                    ctx.i8_type(),
-                                    "str_len_to_i8",
-                                );
-
-                                let final_byte = builder.build_or(
-                                    final_byte,
-                                    ctx.i8_type().const_int(0b1000_0000, false),
-                                    "str_len_set_discriminant",
-                                );
-
-                                let final_byte_ptr = unsafe {
-                                    builder.build_in_bounds_gep(
-                                        combined_str_ptr,
-                                        &[ctx
                 .i8_type()
-                                            .const_int(env.small_str_bytes() as u64 - 1, false)],
+                .const_int(inplace as u64, false)
-                                        "str_literal_final_byte",
+                .into(),
-                                    )
+            str1_i128.into(),
-                                };
+            str2_i128.into(),
-
+        ],
-                                builder.build_store(final_byte_ptr, final_byte);
+        &bitcode::STR_CONCAT,
-
-                                builder.build_load(
-                                    builder
-                                        .build_bitcast(
-                                            combined_str_ptr,
-                                            collection(ctx, env.ptr_bytes)
-                                                .ptr_type(AddressSpace::Generic),
-                                            "cast_collection",
-                                        )
-                                        .into_pointer_value(),
-                                    "small_str_array",
-                                )
-                            };
-
-                            // If the combined length fits in a small string,
-                            // write into a small string!
-                            build_basic_phi2(
-                                env,
-                                parent,
-                                is_big,
-                                // the result of a Str.concat is most likely big
-                                if_big,
-                                if_small,
-                                BasicTypeEnum::StructType(collection(ctx, env.ptr_bytes)),
-                            )
-                        };
-
-                        build_basic_phi2(
-                            env,
-                            parent,
-                            second_str_length_comparison,
-                            if_second_str_is_not_empty,
-                            if_second_str_is_empty,
-                            BasicTypeEnum::StructType(collection(ctx, env.ptr_bytes)),
-                        )
-                    };
-
-                    build_basic_phi2(
-                        env,
-                        parent,
-                        first_str_length_comparison,
-                        if_first_str_is_not_empty,
-                        if_first_str_is_empty,
-                        BasicTypeEnum::StructType(collection(ctx, env.ptr_bytes)),
-                    )
-                },
-            )
-        },
-    )
-}
-
-/// Obtain the string's length, cast from i8 to usize
-fn str_len_from_final_byte<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    final_byte: IntValue<'ctx>,
-) -> IntValue<'ctx> {
-    let builder = env.builder;
-    let ctx = env.context;
-    let bitmask = ctx.i8_type().const_int(0b0111_1111, false);
-    let len_i8 = builder.build_and(final_byte, bitmask, "small_str_length");
-
-    builder.build_int_cast(len_i8, env.ptr_int(), "len_as_usize")
-}
-
-/// Used by LowLevel::StrIsEmpty
-pub fn str_len<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    parent: FunctionValue<'ctx>,
-    wrapper_ptr: PointerValue<'ctx>,
-) -> IntValue<'ctx> {
-    let builder = env.builder;
-
-    let if_small = |final_byte| {
-        let len = str_len_from_final_byte(env, final_byte);
-
-        BasicValueEnum::IntValue(len)
-    };
-
-    let if_big = |_| {
-        let len = big_str_len(
-            builder,
-            builder
-                .build_load(wrapper_ptr, "big_str")
-                .into_struct_value(),
-        );
-
-        BasicValueEnum::IntValue(len)
-    };
-
-    if_small_str(
-        env,
-        parent,
-        wrapper_ptr,
-        if_small,
-        if_big,
-        BasicTypeEnum::IntType(env.ptr_int()),
-    )
-    .into_int_value()
-}
-
-fn load_str<'a, 'ctx, 'env, Callback>(
-    env: &Env<'a, 'ctx, 'env>,
-    parent: FunctionValue<'ctx>,
-    wrapper_ptr: PointerValue<'ctx>,
-    ret_type: BasicTypeEnum<'ctx>,
-    cb: Callback,
-) -> BasicValueEnum<'ctx>
-where
-    Callback: Fn(PointerValue<'ctx>, IntValue<'ctx>, Smallness) -> BasicValueEnum<'ctx>,
-{
-    let builder = env.builder;
-
-    let if_small = |final_byte| {
-        cb(
-            cast_str_wrapper_to_array(env, wrapper_ptr),
-            str_len_from_final_byte(env, final_byte),
-            Smallness::Small,
-        )
-    };
-
-    let if_big = |wrapper_struct| {
-        let list_ptr = load_list_ptr(
-            builder,
-            wrapper_struct,
-            env.context.i8_type().ptr_type(AddressSpace::Generic),
-        );
-
-        cb(
-            list_ptr,
-            big_str_len(builder, wrapper_struct),
-            Smallness::Big,
-        )
-    };
-
-    if_small_str(env, parent, wrapper_ptr, if_small, if_big, ret_type)
-}
-
-#[derive(Debug, Copy, Clone)]
-enum Smallness {
-    Small,
-    Big,
-}
-
-fn clone_nonempty_str<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    inplace: InPlace,
-    smallness: Smallness,
-    len: IntValue<'ctx>,
-    bytes_ptr: PointerValue<'ctx>,
-) -> (StructValue<'ctx>, PointerValue<'ctx>) {
-    let builder = env.builder;
-    let ctx = env.context;
-    let ptr_bytes = env.ptr_bytes;
-
-    // Allocate space for the new str that we'll copy into.
-    match smallness {
-        Smallness::Small => {
-            let wrapper_struct_ptr = cast_str_bytes_to_wrapper(env, bytes_ptr);
-            let wrapper_struct = builder.build_load(wrapper_struct_ptr, "str_wrapper");
-            let alloca = builder.build_alloca(collection(ctx, ptr_bytes), "small_str_clone");
-
-            builder.build_store(alloca, wrapper_struct);
-
-            (wrapper_struct.into_struct_value(), alloca)
-        }
-        Smallness::Big => {
-            let clone_ptr = allocate_list(env, inplace, &CHAR_LAYOUT, len);
-
-            // TODO check if malloc returned null; if so, runtime error for OOM!
-
-            // Copy the bytes from the original array into the new
-            // one we just malloc'd.
-            builder
-                .build_memcpy(clone_ptr, ptr_bytes, bytes_ptr, ptr_bytes, len)
-                .unwrap();
-
-            // Create a fresh wrapper struct for the newly populated array
-            let struct_type = collection(ctx, env.ptr_bytes);
-            let mut struct_val;
-
-            // Store the pointer
-            struct_val = builder
-                .build_insert_value(
-                    struct_type.get_undef(),
-                    clone_ptr,
-                    Builtin::WRAPPER_PTR,
-                    "insert_ptr",
-                )
-                .unwrap();
-
-            // Store the length
-            struct_val = builder
-                .build_insert_value(struct_val, len, Builtin::WRAPPER_LEN, "insert_len")
-                .unwrap();
-
-            let answer = builder
-                .build_bitcast(
-                    struct_val.into_struct_value(),
-                    collection(ctx, ptr_bytes),
-                    "cast_collection",
     )
     .into_struct_value();
 
-            (answer, clone_ptr)
+    zig_str_to_struct(env, zig_result).into()
-        }
-    }
 }
 
-fn cast_str_bytes_to_wrapper<'a, 'ctx, 'env>(
+pub fn str_number_of_bytes<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
-    bytes_ptr: PointerValue<'ctx>,
+    scope: &Scope<'a, 'ctx>,
-) -> PointerValue<'ctx> {
+    str_symbol: Symbol,
-    let struct_ptr_type = collection(env.context, env.ptr_bytes).ptr_type(AddressSpace::Generic);
+) -> IntValue<'ctx> {
+    let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
 
+    // the builtin will always return an u64
+    let length =
+        call_bitcode_fn(env, &[str_i128.into()], &bitcode::STR_NUMBER_OF_BYTES).into_int_value();
+
+    // cast to the appropriate usize of the current build
     env.builder
-        .build_bitcast(bytes_ptr, struct_ptr_type, "str_as_struct_ptr")
+        .build_int_cast(length, env.ptr_int(), "len_as_usize")
-        .into_pointer_value()
-}
-
-fn cast_str_wrapper_to_array<'a, 'ctx, 'env>(
-    env: &Env<'a, 'ctx, 'env>,
-    wrapper_ptr: PointerValue<'ctx>,
-) -> PointerValue<'ctx> {
-    let array_ptr_type = env.context.i8_type().ptr_type(AddressSpace::Generic);
-
-    env.builder
-        .build_bitcast(wrapper_ptr, array_ptr_type, "str_as_array_ptr")
-        .into_pointer_value()
-}
-
-fn if_small_str<'a, 'ctx, 'env, IfSmallFn, IfBigFn>(
-    env: &Env<'a, 'ctx, 'env>,
-    parent: FunctionValue<'ctx>,
-    wrapper_ptr: PointerValue<'ctx>,
-    mut if_small: IfSmallFn,
-    mut if_big: IfBigFn,
-    ret_type: BasicTypeEnum<'ctx>,
-) -> BasicValueEnum<'ctx>
-where
-    IfSmallFn: FnMut(IntValue<'ctx>) -> BasicValueEnum<'ctx>,
-    IfBigFn: FnMut(StructValue<'ctx>) -> BasicValueEnum<'ctx>,
-{
-    let builder = env.builder;
-    let ctx = env.context;
-    let byte_array_ptr = cast_str_wrapper_to_array(env, wrapper_ptr);
-    let final_byte_ptr = unsafe {
-        builder.build_in_bounds_gep(
-            byte_array_ptr,
-            &[ctx
-                .i8_type()
-                .const_int(env.small_str_bytes() as u64 - 1, false)],
-            "final_byte_ptr",
-        )
-    };
-
-    let final_byte = builder
-        .build_load(final_byte_ptr, "load_final_byte")
-        .into_int_value();
-
-    let bitmask = ctx.i8_type().const_int(0b1000_0000, false);
-
-    let is_small_i8 = builder.build_int_compare(
-        IntPredicate::NE,
-        ctx.i8_type().const_zero(),
-        builder.build_and(final_byte, bitmask, "is_small"),
-        "is_small_comparison",
-    );
-
-    let is_small = builder.build_int_cast(is_small_i8, ctx.bool_type(), "is_small_as_bool");
-
-    build_basic_phi2(
-        env,
-        parent,
-        is_small,
-        || if_small(final_byte),
-        || {
-            if_big(
-                builder
-                    .build_load(wrapper_ptr, "load_wrapper_struct")
-                    .into_struct_value(),
-            )
-        },
-        ret_type,
-    )
-}
-
-fn big_str_len<'ctx>(builder: &Builder<'ctx>, wrapper_struct: StructValue<'ctx>) -> IntValue<'ctx> {
-    builder
-        .build_extract_value(wrapper_struct, Builtin::WRAPPER_LEN, "big_str_len")
-        .unwrap()
-        .into_int_value()
-}
-
-fn str_is_not_empty<'ctx>(env: &Env<'_, 'ctx, '_>, len: IntValue<'ctx>) -> IntValue<'ctx> {
-    env.builder.build_int_compare(
-        IntPredicate::UGT,
-        len,
-        env.ptr_int().const_zero(),
-        "str_len_is_nonzero",
-    )
 }
 
 /// Str.startsWith : Str, Str -> Bool
 pub fn str_starts_with<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
-    _inplace: InPlace,
     scope: &Scope<'a, 'ctx>,
-    parent: FunctionValue<'ctx>,
     str_symbol: Symbol,
     prefix_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
-    let ctx = env.context;
+    let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
+    let prefix_i128 = str_symbol_to_i128(env, scope, prefix_symbol);
 
-    let str_ptr = ptr_from_symbol(scope, str_symbol);
-    let prefix_ptr = ptr_from_symbol(scope, prefix_symbol);
-
-    let ret_type = BasicTypeEnum::IntType(ctx.bool_type());
-
-    load_str(
-        env,
-        parent,
-        *str_ptr,
-        ret_type,
-        |str_bytes_ptr, str_len, _str_smallness| {
-            load_str(
-                env,
-                parent,
-                *prefix_ptr,
-                ret_type,
-                |prefix_bytes_ptr, prefix_len, _prefix_smallness| {
     call_bitcode_fn(
         env,
-                        &[
+        &[str_i128.into(), prefix_i128.into()],
-                            BasicValueEnum::PointerValue(str_bytes_ptr),
-                            BasicValueEnum::IntValue(str_len),
-                            BasicValueEnum::PointerValue(prefix_bytes_ptr),
-                            BasicValueEnum::IntValue(prefix_len),
-                        ],
         &bitcode::STR_STARTS_WITH,
     )
-                },
+}
-            )
+
-        },
+/// Str.endsWith : Str, Str -> Bool
+pub fn str_ends_with<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    scope: &Scope<'a, 'ctx>,
+    str_symbol: Symbol,
+    prefix_symbol: Symbol,
+) -> BasicValueEnum<'ctx> {
+    let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
+    let prefix_i128 = str_symbol_to_i128(env, scope, prefix_symbol);
+
+    call_bitcode_fn(
+        env,
+        &[str_i128.into(), prefix_i128.into()],
+        &bitcode::STR_ENDS_WITH,
     )
 }
 
@@ -718,28 +204,26 @@ pub fn str_starts_with<'a, 'ctx, 'env>(
 pub fn str_count_graphemes<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     scope: &Scope<'a, 'ctx>,
-    parent: FunctionValue<'ctx>,
     str_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
-    let ctx = env.context;
+    let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
 
-    let sym_str_ptr = ptr_from_symbol(scope, str_symbol);
-    let ret_type = BasicTypeEnum::IntType(ctx.i64_type());
-
-    load_str(
-        env,
-        parent,
-        *sym_str_ptr,
-        ret_type,
-        |str_ptr, str_len, _str_smallness| {
     call_bitcode_fn(
         env,
-                &[
+        &[str_i128.into()],
-                    BasicValueEnum::PointerValue(str_ptr),
-                    BasicValueEnum::IntValue(str_len),
-                ],
         &bitcode::STR_COUNT_GRAPEHEME_CLUSTERS,
     )
-        },
+}
-    )
+
+/// Str.fromInt : Int -> Str
+pub fn str_from_int<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    scope: &Scope<'a, 'ctx>,
+    int_symbol: Symbol,
+) -> BasicValueEnum<'ctx> {
+    let int = load_symbol(env, scope, &int_symbol);
+
+    let zig_result = call_bitcode_fn(env, &[int], &bitcode::STR_FROM_INT).into_struct_value();
+
+    zig_str_to_struct(env, zig_result).into()
 }

compiler/gen/src/llvm/refcounting.rs

@@ -2,7 +2,7 @@ use crate::llvm::build::{
     cast_basic_basic, cast_struct_struct, create_entry_block_alloca, set_name, Env, Scope,
     FAST_CALL_CONV, LLVM_SADD_WITH_OVERFLOW_I64,
 };
-use crate::llvm::build_list::list_len;
+use crate::llvm::build_list::{incrementing_elem_loop, list_len, load_list};
 use crate::llvm::convert::{basic_type_from_layout, block_of_memory, ptr_int};
 use bumpalo::collections::Vec;
 use inkwell::context::Context;
@@ -367,7 +367,6 @@ fn decrement_refcount_builtin<'a, 'ctx, 'env>(
         List(memory_mode, element_layout) => {
             let wrapper_struct = value.into_struct_value();
             if element_layout.contains_refcounted() {
-                use crate::llvm::build_list::{incrementing_elem_loop, load_list};
                 use inkwell::types::BasicType;
 
                 let ptr_type =
@@ -451,7 +450,6 @@ fn increment_refcount_builtin<'a, 'ctx, 'env>(
         List(memory_mode, element_layout) => {
             let wrapper_struct = value.into_struct_value();
             if element_layout.contains_refcounted() {
-                use crate::llvm::build_list::{incrementing_elem_loop, load_list};
                 use inkwell::types::BasicType;
 
                 let ptr_type =

compiler/gen/tests/gen_list.rs

@@ -557,6 +557,26 @@ mod gen_list {
         );
     }
 
+    #[test]
+    fn list_map_closure() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                pi : F64
+                pi = 3.14
+
+                single : List F64
+                single =
+                    [ 0 ]
+
+                List.map single (\x -> x + pi)
+                "#
+            ),
+            RocList::from_slice(&[3.14]),
+            RocList<f64>
+        );
+    }
+
     #[test]
     fn list_join_empty_list() {
         assert_evals_to!("List.join []", RocList::from_slice(&[]), RocList<i64>);

compiler/gen/tests/gen_str.rs

@@ -433,6 +433,13 @@ mod gen_str {
         assert_evals_to!(r#"Str.startsWith "" "hello world""#, false, bool);
     }
 
+    #[test]
+    fn str_ends_with() {
+        assert_evals_to!(r#"Str.endsWith "hello world" "world""#, true, bool);
+        assert_evals_to!(r#"Str.endsWith "nope" "hello world""#, false, bool);
+        assert_evals_to!(r#"Str.endsWith "" "hello world""#, false, bool);
+    }
+
     #[test]
     fn str_count_graphemes_small_str() {
         assert_evals_to!(r#"Str.countGraphemes "å🤔""#, 2, usize);
@@ -483,4 +490,29 @@ mod gen_str {
     fn str_starts_with_false_small_str() {
         assert_evals_to!(r#"Str.startsWith "1234" "23""#, false, bool);
     }
+
+    #[test]
+    fn str_from_int() {
+        assert_evals_to!(
+            r#"Str.fromInt 1234"#,
+            roc_std::RocStr::from_slice("1234".as_bytes()),
+            roc_std::RocStr
+        );
+        assert_evals_to!(
+            r#"Str.fromInt 0"#,
+            roc_std::RocStr::from_slice("0".as_bytes()),
+            roc_std::RocStr
+        );
+        assert_evals_to!(
+            r#"Str.fromInt -1"#,
+            roc_std::RocStr::from_slice("-1".as_bytes()),
+            roc_std::RocStr
+        );
+
+        let max = format!("{}", i64::MAX);
+        assert_evals_to!(r#"Str.fromInt Num.maxInt"#, &max, &'static str);
+
+        let min = format!("{}", i64::MIN);
+        assert_evals_to!(r#"Str.fromInt Num.minInt"#, &min, &'static str);
+    }
 }

compiler/gen_dev/Cargo.toml

@@ -42,3 +42,6 @@ bumpalo = { version = "3.2", features = ["collections"] }
 libc = "0.2"
 tempfile = "3.1.0"
 itertools = "0.9"
+
+[features]
+target-aarch64 = ["roc_build/target-aarch64"]

compiler/gen_dev/src/generic64/aarch64.rs

@@ -0,0 +1,814 @@
+use crate::generic64::{Assembler, CallConv, GPRegTrait};
+use bumpalo::collections::Vec;
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
+#[allow(dead_code)]
+pub enum AArch64GPReg {
+    X0 = 0,
+    X1 = 1,
+    X2 = 2,
+    X3 = 3,
+    X4 = 4,
+    X5 = 5,
+    X6 = 6,
+    X7 = 7,
+    XR = 8,
+    X9 = 9,
+    X10 = 10,
+    X11 = 11,
+    X12 = 12,
+    X13 = 13,
+    X14 = 14,
+    X15 = 15,
+    IP0 = 16,
+    IP1 = 17,
+    PR = 18,
+    X19 = 19,
+    X20 = 20,
+    X21 = 21,
+    X22 = 22,
+    X23 = 23,
+    X24 = 24,
+    X25 = 25,
+    X26 = 26,
+    X27 = 27,
+    X28 = 28,
+    FP = 29,
+    LR = 30,
+    /// This can mean Zero or Stack Pointer depending on the context.
+    ZRSP = 31,
+}
+
+impl GPRegTrait for AArch64GPReg {}
+
+pub struct AArch64Assembler {}
+
+// AArch64Call may need to eventually be split by OS,
+// but I think with how we use it, they may all be the same.
+pub struct AArch64Call {}
+
+const STACK_ALIGNMENT: u8 = 16;
+
+impl CallConv<AArch64GPReg> for AArch64Call {
+    const GP_PARAM_REGS: &'static [AArch64GPReg] = &[
+        AArch64GPReg::X0,
+        AArch64GPReg::X1,
+        AArch64GPReg::X2,
+        AArch64GPReg::X3,
+        AArch64GPReg::X4,
+        AArch64GPReg::X5,
+        AArch64GPReg::X6,
+        AArch64GPReg::X7,
+    ];
+    const GP_RETURN_REGS: &'static [AArch64GPReg] = Self::GP_PARAM_REGS;
+    const GP_DEFAULT_FREE_REGS: &'static [AArch64GPReg] = &[
+        // The regs we want to use first should be at the end of this vec.
+        // We will use pop to get which reg to use next
+
+        // Don't use frame pointer: AArch64GPReg::FP,
+        // Don't user indirect result location: AArch64GPReg::XR,
+        // Don't use platform register: AArch64GPReg::PR,
+        // Don't use link register: AArch64GPReg::LR,
+        // Don't use zero register/stack pointer: AArch64GPReg::ZRSP,
+
+        // Use callee saved regs last.
+        AArch64GPReg::X19,
+        AArch64GPReg::X20,
+        AArch64GPReg::X21,
+        AArch64GPReg::X22,
+        AArch64GPReg::X23,
+        AArch64GPReg::X24,
+        AArch64GPReg::X25,
+        AArch64GPReg::X26,
+        AArch64GPReg::X27,
+        AArch64GPReg::X28,
+        // Use caller saved regs first.
+        AArch64GPReg::X0,
+        AArch64GPReg::X1,
+        AArch64GPReg::X2,
+        AArch64GPReg::X3,
+        AArch64GPReg::X4,
+        AArch64GPReg::X5,
+        AArch64GPReg::X6,
+        AArch64GPReg::X7,
+        AArch64GPReg::X9,
+        AArch64GPReg::X10,
+        AArch64GPReg::X11,
+        AArch64GPReg::X12,
+        AArch64GPReg::X13,
+        AArch64GPReg::X14,
+        AArch64GPReg::X15,
+        AArch64GPReg::IP0,
+        AArch64GPReg::IP1,
+    ];
+
+    const SHADOW_SPACE_SIZE: u8 = 0;
+
+    #[inline(always)]
+    fn callee_saved(reg: &AArch64GPReg) -> bool {
+        matches!(
+            reg,
+            AArch64GPReg::X19
+                | AArch64GPReg::X20
+                | AArch64GPReg::X21
+                | AArch64GPReg::X22
+                | AArch64GPReg::X23
+                | AArch64GPReg::X24
+                | AArch64GPReg::X25
+                | AArch64GPReg::X26
+                | AArch64GPReg::X27
+                | AArch64GPReg::X28
+        )
+    }
+
+    #[inline(always)]
+    fn setup_stack<'a>(
+        buf: &mut Vec<'a, u8>,
+        leaf_function: bool,
+        saved_regs: &[AArch64GPReg],
+        requested_stack_size: i32,
+    ) -> Result<i32, String> {
+        // full size is upcast to i64 to make sure we don't overflow here.
+        let mut full_size = 8 * saved_regs.len() as i64 + requested_stack_size as i64;
+        if !leaf_function {
+            full_size += 8;
+        }
+        let alignment = if full_size <= 0 {
+            0
+        } else {
+            full_size % STACK_ALIGNMENT as i64
+        };
+        let offset = if alignment == 0 {
+            0
+        } else {
+            STACK_ALIGNMENT - alignment as u8
+        };
+        if let Some(aligned_stack_size) =
+            requested_stack_size.checked_add(8 * saved_regs.len() as i32 + offset as i32)
+        {
+            if aligned_stack_size > 0 {
+                AArch64Assembler::sub_reg64_reg64_imm32(
+                    buf,
+                    AArch64GPReg::ZRSP,
+                    AArch64GPReg::ZRSP,
+                    aligned_stack_size,
+                );
+
+                // All the following stores could be optimized by using `STP` to store pairs.
+                let mut offset = aligned_stack_size;
+                if !leaf_function {
+                    offset -= 8;
+                    AArch64Assembler::mov_stack32_reg64(buf, offset, AArch64GPReg::LR);
+                    offset -= 8;
+                    AArch64Assembler::mov_stack32_reg64(buf, offset, AArch64GPReg::FP);
+                }
+                for reg in saved_regs {
+                    offset -= 8;
+                    AArch64Assembler::mov_stack32_reg64(buf, offset, *reg);
+                }
+                Ok(aligned_stack_size)
+            } else {
+                Ok(0)
+            }
+        } else {
+            Err("Ran out of stack space".to_string())
+        }
+    }
+
+    #[inline(always)]
+    fn cleanup_stack<'a>(
+        buf: &mut Vec<'a, u8>,
+        leaf_function: bool,
+        saved_regs: &[AArch64GPReg],
+        aligned_stack_size: i32,
+    ) -> Result<(), String> {
+        if aligned_stack_size > 0 {
+            // All the following stores could be optimized by using `STP` to store pairs.
+            let mut offset = aligned_stack_size;
+            if !leaf_function {
+                offset -= 8;
+                AArch64Assembler::mov_reg64_stack32(buf, AArch64GPReg::LR, offset);
+                offset -= 8;
+                AArch64Assembler::mov_reg64_stack32(buf, AArch64GPReg::FP, offset);
+            }
+            for reg in saved_regs {
+                offset -= 8;
+                AArch64Assembler::mov_reg64_stack32(buf, *reg, offset);
+            }
+            AArch64Assembler::add_reg64_reg64_imm32(
+                buf,
+                AArch64GPReg::ZRSP,
+                AArch64GPReg::ZRSP,
+                aligned_stack_size,
+            );
+        }
+        Ok(())
+    }
+}
+
+impl Assembler<AArch64GPReg> for AArch64Assembler {
+    #[inline(always)]
+    fn abs_reg64_reg64<'a>(_buf: &mut Vec<'a, u8>, _dst: AArch64GPReg, _src: AArch64GPReg) {
+        unimplemented!("abs_reg64_reg64 is not yet implement for AArch64");
+    }
+
+    #[inline(always)]
+    fn add_reg64_reg64_imm32<'a>(
+        buf: &mut Vec<'a, u8>,
+        dst: AArch64GPReg,
+        src: AArch64GPReg,
+        imm32: i32,
+    ) {
+        if imm32 < 0 {
+            unimplemented!("immediate addition with values less than 0 are not yet implemented");
+        } else if imm32 < 0xFFF {
+            add_reg64_reg64_imm12(buf, dst, src, imm32 as u16);
+        } else {
+            unimplemented!(
+                "immediate additions with values greater than 12bits are not yet implemented"
+            );
+        }
+    }
+
+    #[inline(always)]
+    fn add_reg64_reg64_reg64<'a>(
+        buf: &mut Vec<'a, u8>,
+        dst: AArch64GPReg,
+        src1: AArch64GPReg,
+        src2: AArch64GPReg,
+    ) {
+        add_reg64_reg64_reg64(buf, dst, src1, src2);
+    }
+
+    #[inline(always)]
+    fn mov_reg64_imm64<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, imm: i64) {
+        let mut remaining = imm as u64;
+        movz_reg64_imm16(buf, dst, remaining as u16, 0);
+        remaining >>= 16;
+        if remaining > 0 {
+            movk_reg64_imm16(buf, dst, remaining as u16, 1);
+        }
+        remaining >>= 16;
+        if remaining > 0 {
+            movk_reg64_imm16(buf, dst, remaining as u16, 2);
+        }
+        remaining >>= 16;
+        if remaining > 0 {
+            movk_reg64_imm16(buf, dst, remaining as u16, 3);
+        }
+    }
+
+    #[inline(always)]
+    fn mov_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, src: AArch64GPReg) {
+        mov_reg64_reg64(buf, dst, src);
+    }
+
+    #[inline(always)]
+    fn mov_reg64_stack32<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, offset: i32) {
+        if offset < 0 {
+            unimplemented!("negative stack offsets are not yet implement for AArch64");
+        } else if offset < (0xFFF << 8) {
+            debug_assert!(offset % 8 == 0);
+            ldr_reg64_imm12(buf, dst, AArch64GPReg::ZRSP, (offset as u16) >> 3);
+        } else {
+            unimplemented!("stack offsets over 32k are not yet implement for AArch64");
+        }
+    }
+
+    #[inline(always)]
+    fn mov_stack32_reg64<'a>(buf: &mut Vec<'a, u8>, offset: i32, src: AArch64GPReg) {
+        if offset < 0 {
+            unimplemented!("negative stack offsets are not yet implement for AArch64");
+        } else if offset < (0xFFF << 8) {
+            debug_assert!(offset % 8 == 0);
+            str_reg64_imm12(buf, src, AArch64GPReg::ZRSP, (offset as u16) >> 3);
+        } else {
+            unimplemented!("stack offsets over 32k are not yet implement for AArch64");
+        }
+    }
+
+    #[inline(always)]
+    fn sub_reg64_reg64_imm32<'a>(
+        buf: &mut Vec<'a, u8>,
+        dst: AArch64GPReg,
+        src: AArch64GPReg,
+        imm32: i32,
+    ) {
+        if imm32 < 0 {
+            unimplemented!(
+                "immediate subtractions with values less than 0 are not yet implemented"
+            );
+        } else if imm32 < 0xFFF {
+            sub_reg64_reg64_imm12(buf, dst, src, imm32 as u16);
+        } else {
+            unimplemented!(
+                "immediate subtractions with values greater than 12bits are not yet implemented"
+            );
+        }
+    }
+
+    #[inline(always)]
+    fn ret<'a>(buf: &mut Vec<'a, u8>) {
+        ret_reg64(buf, AArch64GPReg::LR)
+    }
+}
+
+impl AArch64Assembler {}
+
+/// AArch64Instruction, maps all instructions to an enum.
+/// Decoding the function should be cheap because we will always inline.
+/// All of the operations should resolved by constants, leave just some bit manipulation.
+/// Enums may not be complete since we will only add what we need.
+#[derive(Debug)]
+enum AArch64Instruction {
+    _Reserved,
+    _SVE,
+    DPImm(DPImmGroup),
+    Branch(BranchGroup),
+    LdStr(LdStrGroup),
+    DPReg(DPRegGroup),
+    _DPFloat,
+}
+
+#[derive(Debug)]
+enum BranchGroup {
+    UnconditionBranchReg {
+        opc: u8,
+        op2: u8,
+        op3: u8,
+        reg_n: AArch64GPReg,
+        op4: u8,
+    },
+}
+
+#[derive(Debug)]
+enum DPRegGroup {
+    AddSubShifted {
+        sf: bool,
+        subtract: bool,
+        set_flags: bool,
+        shift: u8,
+        reg_m: AArch64GPReg,
+        imm6: u8,
+        reg_n: AArch64GPReg,
+        reg_d: AArch64GPReg,
+    },
+    Logical {
+        sf: bool,
+        op: DPRegLogicalOp,
+        shift: u8,
+        reg_m: AArch64GPReg,
+        imm6: u8,
+        reg_n: AArch64GPReg,
+        reg_d: AArch64GPReg,
+    },
+}
+
+#[derive(Debug)]
+enum DPImmGroup {
+    AddSubImm {
+        sf: bool,
+        subtract: bool,
+        set_flags: bool,
+        shift: bool,
+        imm12: u16,
+        reg_n: AArch64GPReg,
+        reg_d: AArch64GPReg,
+    },
+    MoveWide {
+        sf: bool,
+        opc: u8,
+        hw: u8,
+        imm16: u16,
+        reg_d: AArch64GPReg,
+    },
+}
+
+#[derive(Debug)]
+enum LdStrGroup {
+    UnsignedImm {
+        size: u8,
+        v: bool,
+        opc: u8,
+        imm12: u16,
+        reg_n: AArch64GPReg,
+        reg_t: AArch64GPReg,
+    },
+}
+
+#[derive(Debug)]
+#[allow(dead_code)]
+enum DPRegLogicalOp {
+    AND,
+    BIC,
+    ORR,
+    ORN,
+    EOR,
+    EON,
+    ANDS,
+    BICS,
+}
+
+#[inline(always)]
+fn build_instruction(inst: AArch64Instruction) -> [u8; 4] {
+    let mut out: u32 = 0;
+    match inst {
+        AArch64Instruction::Branch(branch) => {
+            out |= 0b101 << 26;
+            match branch {
+                BranchGroup::UnconditionBranchReg {
+                    opc,
+                    op2,
+                    op3,
+                    reg_n,
+                    op4,
+                } => {
+                    debug_assert!(opc <= 0b1111);
+                    debug_assert!(op2 <= 0b11111);
+                    debug_assert!(op3 <= 0b111111);
+                    debug_assert!(op4 <= 0b1111);
+                    out |= 0b1101011 << 25;
+                    out |= (opc as u32) << 21;
+                    out |= (op2 as u32) << 16;
+                    out |= (op3 as u32) << 10;
+                    out |= (reg_n as u32) << 5;
+                    out |= op4 as u32;
+                }
+            }
+        }
+        AArch64Instruction::DPImm(dpimm) => {
+            out |= 0b100 << 26;
+            match dpimm {
+                DPImmGroup::MoveWide {
+                    sf,
+                    opc,
+                    hw,
+                    imm16,
+                    reg_d,
+                } => {
+                    out |= (sf as u32) << 31;
+                    out |= (opc as u32) << 29;
+                    out |= 0b101 << 23;
+                    out |= (hw as u32) << 21;
+                    out |= (imm16 as u32) << 5;
+                    out |= reg_d as u32;
+                }
+                DPImmGroup::AddSubImm {
+                    sf,
+                    subtract,
+                    set_flags,
+                    shift,
+                    imm12,
+                    reg_n,
+                    reg_d,
+                } => {
+                    debug_assert!(imm12 <= 0xFFF);
+                    out |= (sf as u32) << 31;
+                    out |= (subtract as u32) << 30;
+                    out |= (set_flags as u32) << 29;
+                    out |= 0b010 << 23;
+                    out |= (shift as u32) << 22;
+                    out |= (imm12 as u32) << 10;
+                    out |= (reg_n as u32) << 5;
+                    out |= reg_d as u32;
+                }
+            }
+        }
+        AArch64Instruction::DPReg(dpreg) => {
+            out |= 0b101 << 25;
+            match dpreg {
+                DPRegGroup::Logical {
+                    sf,
+                    op,
+                    shift,
+                    reg_m,
+                    imm6,
+                    reg_n,
+                    reg_d,
+                } => {
+                    debug_assert!(shift <= 0b11);
+                    debug_assert!(imm6 <= 0b111111);
+                    let (opc, n) = match op {
+                        DPRegLogicalOp::AND => (0b00, 0),
+                        DPRegLogicalOp::BIC => (0b00, 1),
+                        DPRegLogicalOp::ORR => (0b01, 0),
+                        DPRegLogicalOp::ORN => (0b01, 1),
+                        DPRegLogicalOp::EOR => (0b10, 0),
+                        DPRegLogicalOp::EON => (0b10, 1),
+                        DPRegLogicalOp::ANDS => (0b11, 0),
+                        DPRegLogicalOp::BICS => (0b11, 1),
+                    };
+                    out |= (sf as u32) << 31;
+                    out |= opc << 29;
+                    out |= (shift as u32) << 22;
+                    out |= n << 21;
+                    out |= (reg_m as u32) << 16;
+                    out |= (imm6 as u32) << 10;
+                    out |= (reg_n as u32) << 5;
+                    out |= reg_d as u32;
+                }
+                DPRegGroup::AddSubShifted {
+                    sf,
+                    subtract,
+                    set_flags,
+                    shift,
+                    reg_m,
+                    imm6,
+                    reg_n,
+                    reg_d,
+                } => {
+                    debug_assert!(shift <= 0b11);
+                    debug_assert!(imm6 <= 0b111111);
+                    out |= (sf as u32) << 31;
+                    out |= (subtract as u32) << 30;
+                    out |= (set_flags as u32) << 29;
+                    out |= 0b1 << 24;
+                    out |= (shift as u32) << 22;
+                    out |= (reg_m as u32) << 16;
+                    out |= (imm6 as u32) << 10;
+                    out |= (reg_n as u32) << 5;
+                    out |= reg_d as u32;
+                }
+            }
+        }
+        AArch64Instruction::LdStr(ldstr) => {
+            out |= 0b1 << 27;
+            match ldstr {
+                LdStrGroup::UnsignedImm {
+                    size,
+                    v,
+                    opc,
+                    imm12,
+                    reg_n,
+                    reg_t,
+                } => {
+                    debug_assert!(size <= 0b11);
+                    debug_assert!(imm12 <= 0xFFF);
+                    out |= (size as u32) << 30;
+                    out |= 0b11 << 28;
+                    out |= (v as u32) << 26;
+                    out |= 0b1 << 24;
+                    out |= (opc as u32) << 22;
+                    out |= (imm12 as u32) << 10;
+                    out |= (reg_n as u32) << 5;
+                    out |= reg_t as u32;
+                }
+            }
+        }
+        x => unimplemented!("The instruction, {:?}, has not be implemented yet", x),
+    }
+    out.to_le_bytes()
+}
+
+// Below here are the functions for all of the assembly instructions.
+// Their names are based on the instruction and operators combined.
+// You should call `buf.reserve()` if you push or extend more than once.
+// Unit tests are added at the bottom of the file to ensure correct asm generation.
+// Please keep these in alphanumeric order.
+
+/// `ADD Xd, Xn, imm12` -> Add Xn and imm12 and place the result into Xd.
+#[inline(always)]
+fn add_reg64_reg64_imm12<'a>(
+    buf: &mut Vec<'a, u8>,
+    dst: AArch64GPReg,
+    src: AArch64GPReg,
+    imm12: u16,
+) {
+    buf.extend(&build_instruction(AArch64Instruction::DPImm(
+        DPImmGroup::AddSubImm {
+            sf: true,
+            subtract: false,
+            set_flags: false,
+            shift: false,
+            imm12,
+            reg_n: src,
+            reg_d: dst,
+        },
+    )));
+}
+
+/// `ADD Xd, Xm, Xn` -> Add Xm and Xn and place the result into Xd.
+#[inline(always)]
+fn add_reg64_reg64_reg64<'a>(
+    buf: &mut Vec<'a, u8>,
+    dst: AArch64GPReg,
+    src1: AArch64GPReg,
+    src2: AArch64GPReg,
+) {
+    buf.extend(&build_instruction(AArch64Instruction::DPReg(
+        DPRegGroup::AddSubShifted {
+            sf: true,
+            subtract: false,
+            set_flags: false,
+            shift: 0,
+            reg_m: src1,
+            imm6: 0,
+            reg_n: src2,
+            reg_d: dst,
+        },
+    )));
+}
+
+/// `LDR Xt, [Xn, #offset]` -> Load Xn + Offset Xt. ZRSP is SP.
+/// Note: imm12 is the offest divided by 8.
+#[inline(always)]
+fn ldr_reg64_imm12<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, base: AArch64GPReg, imm12: u16) {
+    debug_assert!(imm12 <= 0xFFF);
+    buf.extend(&build_instruction(AArch64Instruction::LdStr(
+        LdStrGroup::UnsignedImm {
+            size: 0b11,
+            v: false,
+            opc: 0b01,
+            imm12,
+            reg_n: base,
+            reg_t: dst,
+        },
+    )));
+}
+
+/// `MOV Xd, Xm` -> Move Xm to Xd.
+#[inline(always)]
+fn mov_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, src: AArch64GPReg) {
+    // MOV is equvalent to `ORR Xd, XZR, XM` in AARCH64.
+    buf.extend(&build_instruction(AArch64Instruction::DPReg(
+        DPRegGroup::Logical {
+            sf: true,
+            op: DPRegLogicalOp::ORR,
+            shift: 0,
+            reg_m: src,
+            imm6: 0,
+            reg_n: AArch64GPReg::ZRSP,
+            reg_d: dst,
+        },
+    )));
+}
+
+/// `MOVK Xd, imm16` -> Keeps Xd and moves an optionally shifted imm16 to Xd.
+#[inline(always)]
+fn movk_reg64_imm16<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, imm16: u16, hw: u8) {
+    debug_assert!(hw <= 0b11);
+    // MOV is equvalent to `ORR Xd, XZR, XM` in AARCH64.
+    buf.extend(&build_instruction(AArch64Instruction::DPImm(
+        DPImmGroup::MoveWide {
+            sf: true,
+            opc: 0b11,
+            hw,
+            imm16,
+            reg_d: dst,
+        },
+    )));
+}
+
+/// `MOVZ Xd, imm16` -> Zeros Xd and moves an optionally shifted imm16 to Xd.
+#[inline(always)]
+fn movz_reg64_imm16<'a>(buf: &mut Vec<'a, u8>, dst: AArch64GPReg, imm16: u16, hw: u8) {
+    debug_assert!(hw <= 0b11);
+    // MOV is equvalent to `ORR Xd, XZR, XM` in AARCH64.
+    buf.extend(&build_instruction(AArch64Instruction::DPImm(
+        DPImmGroup::MoveWide {
+            sf: true,
+            opc: 0b10,
+            hw,
+            imm16,
+            reg_d: dst,
+        },
+    )));
+}
+
+/// `STR Xt, [Xn, #offset]` -> Store Xt to Xn + Offset. ZRSP is SP.
+/// Note: imm12 is the offest divided by 8.
+#[inline(always)]
+fn str_reg64_imm12<'a>(buf: &mut Vec<'a, u8>, src: AArch64GPReg, base: AArch64GPReg, imm12: u16) {
+    debug_assert!(imm12 <= 0xFFF);
+    buf.extend(&build_instruction(AArch64Instruction::LdStr(
+        LdStrGroup::UnsignedImm {
+            size: 0b11,
+            v: false,
+            opc: 0b00,
+            imm12,
+            reg_n: base,
+            reg_t: src,
+        },
+    )));
+}
+
+/// `SUB Xd, Xn, imm12` -> Subtract Xn and imm12 and place the result into Xd.
+#[inline(always)]
+fn sub_reg64_reg64_imm12<'a>(
+    buf: &mut Vec<'a, u8>,
+    dst: AArch64GPReg,
+    src: AArch64GPReg,
+    imm12: u16,
+) {
+    buf.extend(&build_instruction(AArch64Instruction::DPImm(
+        DPImmGroup::AddSubImm {
+            sf: true,
+            subtract: true,
+            set_flags: false,
+            shift: false,
+            imm12,
+            reg_n: src,
+            reg_d: dst,
+        },
+    )));
+}
+
+/// `RET Xn` -> Return to the address stored in Xn.
+#[inline(always)]
+fn ret_reg64<'a>(buf: &mut Vec<'a, u8>, xn: AArch64GPReg) {
+    buf.extend(&build_instruction(AArch64Instruction::Branch(
+        BranchGroup::UnconditionBranchReg {
+            opc: 0b0010,
+            op2: 0b11111,
+            op3: 0b000000,
+            reg_n: xn,
+            op4: 0b000,
+        },
+    )));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_U16: u16 = 0x1234;
+    //const TEST_I32: i32 = 0x12345678;
+    //const TEST_I64: i64 = 0x12345678_9ABCDEF0;
+
+    #[test]
+    fn test_add_reg64_reg64_reg64() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        add_reg64_reg64_reg64(
+            &mut buf,
+            AArch64GPReg::X10,
+            AArch64GPReg::ZRSP,
+            AArch64GPReg::X21,
+        );
+        assert_eq!(&buf, &[0xAA, 0x02, 0x1F, 0x8B]);
+    }
+
+    #[test]
+    fn test_add_reg64_reg64_imm12() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        add_reg64_reg64_imm12(&mut buf, AArch64GPReg::X10, AArch64GPReg::X21, 0x123);
+        assert_eq!(&buf, &[0xAA, 0x8E, 0x04, 0x91]);
+    }
+
+    #[test]
+    fn test_ldr_reg64_imm12() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        ldr_reg64_imm12(&mut buf, AArch64GPReg::X21, AArch64GPReg::ZRSP, 0x123);
+        assert_eq!(&buf, &[0xF5, 0x8F, 0x44, 0xF9]);
+    }
+
+    #[test]
+    fn test_mov_reg64_reg64() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        mov_reg64_reg64(&mut buf, AArch64GPReg::X10, AArch64GPReg::X21);
+        assert_eq!(&buf, &[0xEA, 0x03, 0x15, 0xAA]);
+    }
+
+    #[test]
+    fn test_movk_reg64_imm16() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        movk_reg64_imm16(&mut buf, AArch64GPReg::X21, TEST_U16, 3);
+        assert_eq!(&buf, &[0x95, 0x46, 0xE2, 0xF2]);
+    }
+
+    #[test]
+    fn test_movz_reg64_imm16() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        movz_reg64_imm16(&mut buf, AArch64GPReg::X21, TEST_U16, 3);
+        assert_eq!(&buf, &[0x95, 0x46, 0xE2, 0xD2]);
+    }
+
+    #[test]
+    fn test_str_reg64_imm12() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        str_reg64_imm12(&mut buf, AArch64GPReg::X21, AArch64GPReg::ZRSP, 0x123);
+        assert_eq!(&buf, &[0xF5, 0x8F, 0x04, 0xF9]);
+    }
+
+    #[test]
+    fn test_sub_reg64_reg64_imm12() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        sub_reg64_reg64_imm12(&mut buf, AArch64GPReg::X10, AArch64GPReg::X21, 0x123);
+        assert_eq!(&buf, &[0xAA, 0x8E, 0x04, 0xD1]);
+    }
+
+    #[test]
+    fn test_ret_reg64() {
+        let arena = bumpalo::Bump::new();
+        let mut buf = bumpalo::vec![in &arena];
+        ret_reg64(&mut buf, AArch64GPReg::LR);
+        assert_eq!(&buf, &[0xC0, 0x03, 0x5F, 0xD6]);
+    }
+}

compiler/gen_dev/src/generic64/mod.rs

@@ -1,49 +1,61 @@
 use crate::{Backend, Env, Relocation};
 use bumpalo::collections::Vec;
-use roc_collections::all::{ImSet, MutMap, MutSet};
+use roc_collections::all::{MutMap, MutSet};
 use roc_module::symbol::Symbol;
 use roc_mono::ir::{Literal, Stmt};
 use std::marker::PhantomData;
 use target_lexicon::Triple;
 
+pub mod aarch64;
 pub mod x86_64;
 
-pub trait CallConv<GPReg> {
+pub trait CallConv<GPReg: GPRegTrait> {
-    fn gp_param_regs() -> &'static [GPReg];
+    const GP_PARAM_REGS: &'static [GPReg];
-    fn gp_return_regs() -> &'static [GPReg];
+    const GP_RETURN_REGS: &'static [GPReg];
-    fn gp_default_free_regs() -> &'static [GPReg];
+    const GP_DEFAULT_FREE_REGS: &'static [GPReg];
 
-    // A linear scan of an array may be faster than a set technically.
+    const SHADOW_SPACE_SIZE: u8;
-    // That being said, fastest would likely be a trait based on calling convention/register.
-    fn caller_saved_regs() -> ImSet<GPReg>;
-    fn callee_saved_regs() -> ImSet<GPReg>;
 
-    fn stack_pointer() -> GPReg;
+    fn callee_saved(reg: &GPReg) -> bool;
-    fn frame_pointer() -> GPReg;
+    #[inline(always)]
-
+    fn caller_saved_regs(reg: &GPReg) -> bool {
-    fn shadow_space_size() -> u8;
+        !Self::callee_saved(reg)
-    // It may be worth ignoring the red zone and keeping things simpler.
-    fn red_zone_size() -> u8;
     }
 
-pub trait Assembler<GPReg> {
+    fn setup_stack<'a>(
-    fn add_register64bit_immediate32bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, imm: i32);
+        buf: &mut Vec<'a, u8>,
-    fn add_register64bit_register64bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src: GPReg);
+        leaf_function: bool,
-    fn cmovl_register64bit_register64bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src: GPReg);
+        saved_regs: &[GPReg],
-    fn mov_register64bit_immediate32bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, imm: i32);
+        requested_stack_size: i32,
-    fn mov_register64bit_immediate64bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, imm: i64);
+    ) -> Result<i32, String>;
-    fn mov_register64bit_register64bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src: GPReg);
+    fn cleanup_stack<'a>(
-    fn mov_register64bit_stackoffset32bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, offset: i32);
+        buf: &mut Vec<'a, u8>,
-    fn mov_stackoffset32bit_register64bit<'a>(buf: &mut Vec<'a, u8>, offset: i32, src: GPReg);
+        leaf_function: bool,
-    fn neg_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: GPReg);
+        saved_regs: &[GPReg],
+        aligned_stack_size: i32,
+    ) -> Result<(), String>;
+}
+
+/// Assembler contains calls to the backend assembly generator.
+/// These calls do not necessarily map directly to a single assembly instruction.
+/// They are higher level in cases where an instruction would not be common and shared between multiple architectures.
+/// Thus, some backends will need to use mulitiple instructions to preform a single one of this calls.
+/// Generally, I prefer explicit sources, as opposed to dst being one of the sources. Ex: `x = x + y` would be `add x, x, y` instead of `add x, y`.
+/// dst should always come before sources.
+pub trait Assembler<GPReg: GPRegTrait> {
+    fn abs_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src: GPReg);
+    fn add_reg64_reg64_imm32<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src1: GPReg, imm32: i32);
+    fn add_reg64_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src1: GPReg, src2: GPReg);
+    fn mov_reg64_imm64<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, imm: i64);
+    fn mov_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src: GPReg);
+    fn mov_reg64_stack32<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, offset: i32);
+    fn mov_stack32_reg64<'a>(buf: &mut Vec<'a, u8>, offset: i32, src: GPReg);
+    fn sub_reg64_reg64_imm32<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, src1: GPReg, imm32: i32);
     fn ret<'a>(buf: &mut Vec<'a, u8>);
-    fn sub_register64bit_immediate32bit<'a>(buf: &mut Vec<'a, u8>, dst: GPReg, imm: i32);
-    fn pop_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: GPReg);
-    fn push_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: GPReg);
 }
 
 #[derive(Clone, Debug, PartialEq)]
-enum SymbolStorage<GPReg> {
+enum SymbolStorage<GPReg: GPRegTrait> {
     // These may need layout, but I am not sure.
     // I think whenever a symbol would be used, we specify layout anyways.
     GPRegeg(GPReg),
@@ -69,7 +81,7 @@ pub struct Backend64Bit<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallCo
     literal_map: MutMap<Symbol, Literal<'a>>,
 
     // This should probably be smarter than a vec.
-    // There are certain registers we should always use first. With pushing and poping, this could get mixed.
+    // There are certain registers we should always use first. With pushing and popping, this could get mixed.
     gp_free_regs: Vec<'a, GPReg>,
 
     // The last major thing we need is a way to decide what reg to free when all of them are full.
@@ -109,7 +121,7 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
     }
 
     fn reset(&mut self) {
-        self.stack_size = -(CC::red_zone_size() as i32);
+        self.stack_size = 0;
         self.leaf_function = true;
         self.last_seen_map.clear();
         self.free_map.clear();
@@ -119,13 +131,12 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
         self.gp_free_regs.clear();
         self.gp_used_regs.clear();
         self.gp_free_regs
-            .extend_from_slice(CC::gp_default_free_regs());
+            .extend_from_slice(CC::GP_DEFAULT_FREE_REGS);
     }
 
     fn set_not_leaf_function(&mut self) {
         self.leaf_function = false;
-        // If this is not a leaf function, it can't use the shadow space.
+        self.stack_size = CC::SHADOW_SPACE_SIZE as i32;
-        self.stack_size = CC::shadow_space_size() as i32 - CC::red_zone_size() as i32;
     }
 
     fn literal_map(&mut self) -> &mut MutMap<Symbol, Literal<'a>> {
@@ -147,38 +158,17 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
     fn finalize(&mut self) -> Result<(&'a [u8], &[Relocation]), String> {
         let mut out = bumpalo::vec![in self.env.arena];
 
-        if !self.leaf_function {
+        // Setup stack.
-            // I believe that this will have to move away from push and to mov to be generic across backends.
+        let mut used_regs = bumpalo::vec![in self.env.arena];
-            ASM::push_register64bit(&mut out, CC::frame_pointer());
+        used_regs.extend(&self.used_callee_saved_regs);
-            ASM::mov_register64bit_register64bit(
+        let aligned_stack_size =
-                &mut out,
+            CC::setup_stack(&mut out, self.leaf_function, &used_regs, self.stack_size)?;
-                CC::frame_pointer(),
-                CC::stack_pointer(),
-            );
-        }
-        // Save data in all callee saved regs.
-        let mut pop_order = bumpalo::vec![in self.env.arena];
-        for reg in &self.used_callee_saved_regs {
-            ASM::push_register64bit(&mut out, *reg);
-            pop_order.push(*reg);
-        }
-        if self.stack_size > 0 {
-            ASM::sub_register64bit_immediate32bit(&mut out, CC::stack_pointer(), self.stack_size);
-        }
 
         // Add function body.
         out.extend(&self.buf);
 
-        if self.stack_size > 0 {
+        // Cleanup stack.
-            ASM::add_register64bit_immediate32bit(&mut out, CC::stack_pointer(), self.stack_size);
+        CC::cleanup_stack(&mut out, self.leaf_function, &used_regs, aligned_stack_size)?;
-        }
-        // Restore data in callee saved regs.
-        while let Some(reg) = pop_order.pop() {
-            ASM::pop_register64bit(&mut out, reg);
-        }
-        if !self.leaf_function {
-            ASM::pop_register64bit(&mut out, CC::frame_pointer());
-        }
         ASM::ret(&mut out);
 
         Ok((out.into_bump_slice(), &[]))
@@ -187,9 +177,7 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
     fn build_num_abs_i64(&mut self, dst: &Symbol, src: &Symbol) -> Result<(), String> {
         let dst_reg = self.claim_gp_reg(dst)?;
         let src_reg = self.load_to_reg(src)?;
-        ASM::mov_register64bit_register64bit(&mut self.buf, dst_reg, src_reg);
+        ASM::abs_reg64_reg64(&mut self.buf, dst_reg, src_reg);
-        ASM::neg_register64bit(&mut self.buf, dst_reg);
-        ASM::cmovl_register64bit_register64bit(&mut self.buf, dst_reg, src_reg);
         Ok(())
     }
 
@@ -201,9 +189,8 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
     ) -> Result<(), String> {
         let dst_reg = self.claim_gp_reg(dst)?;
         let src1_reg = self.load_to_reg(src1)?;
-        ASM::mov_register64bit_register64bit(&mut self.buf, dst_reg, src1_reg);
         let src2_reg = self.load_to_reg(src2)?;
-        ASM::add_register64bit_register64bit(&mut self.buf, dst_reg, src2_reg);
+        ASM::add_reg64_reg64_reg64(&mut self.buf, dst_reg, src1_reg, src2_reg);
         Ok(())
     }
 
@@ -212,7 +199,7 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
             Literal::Int(x) => {
                 let reg = self.claim_gp_reg(sym)?;
                 let val = *x;
-                ASM::mov_register64bit_immediate64bit(&mut self.buf, reg, val);
+                ASM::mov_reg64_imm64(&mut self.buf, reg, val);
                 Ok(())
             }
             x => Err(format!("loading literal, {:?}, is not yet implemented", x)),
@@ -234,11 +221,11 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>> Backend<
     fn return_symbol(&mut self, sym: &Symbol) -> Result<(), String> {
         let val = self.symbols_map.get(sym);
         match val {
-            Some(SymbolStorage::GPRegeg(reg)) if *reg == CC::gp_return_regs()[0] => Ok(()),
+            Some(SymbolStorage::GPRegeg(reg)) if *reg == CC::GP_RETURN_REGS[0] => Ok(()),
             Some(SymbolStorage::GPRegeg(reg)) => {
                 // If it fits in a general purpose register, just copy it over to.
                 // Technically this can be optimized to produce shorter instructions if less than 64bits.
-                ASM::mov_register64bit_register64bit(&mut self.buf, CC::gp_return_regs()[0], *reg);
+                ASM::mov_reg64_reg64(&mut self.buf, CC::GP_RETURN_REGS[0], *reg);
                 Ok(())
             }
             Some(x) => Err(format!(
@@ -258,7 +245,7 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>>
     fn claim_gp_reg(&mut self, sym: &Symbol) -> Result<GPReg, String> {
         let reg = if !self.gp_free_regs.is_empty() {
             let free_reg = self.gp_free_regs.pop().unwrap();
-            if CC::callee_saved_regs().contains(&free_reg) {
+            if CC::callee_saved(&free_reg) {
                 self.used_callee_saved_regs.insert(free_reg);
             }
             Ok(free_reg)
@@ -291,7 +278,7 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>>
                 let reg = self.claim_gp_reg(sym)?;
                 self.symbols_map
                     .insert(*sym, SymbolStorage::StackAndGPRegeg(reg, offset));
-                ASM::mov_register64bit_stackoffset32bit(&mut self.buf, reg, offset as i32);
+                ASM::mov_reg64_stack32(&mut self.buf, reg, offset as i32);
                 Ok(reg)
             }
             None => Err(format!("Unknown symbol: {}", sym)),
@@ -302,19 +289,9 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>>
         let val = self.symbols_map.remove(sym);
         match val {
             Some(SymbolStorage::GPRegeg(reg)) => {
-                let offset = self.stack_size;
+                let offset = self.increase_stack_size(8)?;
-                self.stack_size += 8;
+                ASM::mov_stack32_reg64(&mut self.buf, offset as i32, reg);
-                if let Some(size) = self.stack_size.checked_add(8) {
+                self.symbols_map.insert(*sym, SymbolStorage::Stack(offset));
-                    self.stack_size = size;
-                } else {
-                    return Err(format!(
-                        "Ran out of stack space while saving symbol: {}",
-                        sym
-                    ));
-                }
-                ASM::mov_stackoffset32bit_register64bit(&mut self.buf, offset as i32, reg);
-                self.symbols_map
-                    .insert(*sym, SymbolStorage::Stack(offset as i32));
                 Ok(())
             }
             Some(SymbolStorage::StackAndGPRegeg(_, offset)) => {
@@ -328,4 +305,16 @@ impl<'a, GPReg: GPRegTrait, ASM: Assembler<GPReg>, CC: CallConv<GPReg>>
             None => Err(format!("Unknown symbol: {}", sym)),
         }
     }
+
+    /// increase_stack_size increase the current stack size and returns the offset of the stack.
+    fn increase_stack_size(&mut self, amount: i32) -> Result<i32, String> {
+        debug_assert!(amount > 0);
+        let offset = self.stack_size;
+        if let Some(new_size) = self.stack_size.checked_add(amount) {
+            self.stack_size = new_size;
+            Ok(offset)
+        } else {
+            Err("Ran out of stack space".to_string())
+        }
+    }
 }

compiler/gen_dev/src/generic64/x86_64.rs

@@ -1,6 +1,5 @@
 use crate::generic64::{Assembler, CallConv, GPRegTrait};
 use bumpalo::collections::Vec;
-use roc_collections::all::ImSet;
 
 // Not sure exactly how I want to represent registers.
 // If we want max speed, we would likely make them structs that impl the same trait to avoid ifs.
@@ -26,10 +25,312 @@ pub enum X86_64GPReg {
 
 impl GPRegTrait for X86_64GPReg {}
 
+pub struct X86_64Assembler {}
+pub struct X86_64WindowsFastcall {}
+pub struct X86_64SystemV {}
+
+const STACK_ALIGNMENT: u8 = 16;
+
+impl CallConv<X86_64GPReg> for X86_64SystemV {
+    const GP_PARAM_REGS: &'static [X86_64GPReg] = &[
+        X86_64GPReg::RDI,
+        X86_64GPReg::RSI,
+        X86_64GPReg::RDX,
+        X86_64GPReg::RCX,
+        X86_64GPReg::R8,
+        X86_64GPReg::R9,
+    ];
+    const GP_RETURN_REGS: &'static [X86_64GPReg] = &[X86_64GPReg::RAX, X86_64GPReg::RDX];
+
+    const GP_DEFAULT_FREE_REGS: &'static [X86_64GPReg] = &[
+        // The regs we want to use first should be at the end of this vec.
+        // We will use pop to get which reg to use next
+        // Use callee saved regs last.
+        X86_64GPReg::RBX,
+        // Don't use frame pointer: X86_64GPReg::RBP,
+        X86_64GPReg::R12,
+        X86_64GPReg::R13,
+        X86_64GPReg::R14,
+        X86_64GPReg::R15,
+        // Use caller saved regs first.
+        X86_64GPReg::RAX,
+        X86_64GPReg::RCX,
+        X86_64GPReg::RDX,
+        // Don't use stack pionter: X86_64GPReg::RSP,
+        X86_64GPReg::RSI,
+        X86_64GPReg::RDI,
+        X86_64GPReg::R8,
+        X86_64GPReg::R9,
+        X86_64GPReg::R10,
+        X86_64GPReg::R11,
+    ];
+    const SHADOW_SPACE_SIZE: u8 = 0;
+
+    #[inline(always)]
+    fn callee_saved(reg: &X86_64GPReg) -> bool {
+        matches!(
+            reg,
+            X86_64GPReg::RBX
+                | X86_64GPReg::RBP
+                | X86_64GPReg::R12
+                | X86_64GPReg::R13
+                | X86_64GPReg::R14
+                | X86_64GPReg::R15
+        )
+    }
+
+    #[inline(always)]
+    fn setup_stack<'a>(
+        buf: &mut Vec<'a, u8>,
+        leaf_function: bool,
+        saved_regs: &[X86_64GPReg],
+        requested_stack_size: i32,
+    ) -> Result<i32, String> {
+        x86_64_generic_setup_stack(buf, leaf_function, saved_regs, requested_stack_size)
+    }
+
+    #[inline(always)]
+    fn cleanup_stack<'a>(
+        buf: &mut Vec<'a, u8>,
+        leaf_function: bool,
+        saved_regs: &[X86_64GPReg],
+        aligned_stack_size: i32,
+    ) -> Result<(), String> {
+        x86_64_generic_cleanup_stack(buf, leaf_function, saved_regs, aligned_stack_size)
+    }
+}
+
+impl CallConv<X86_64GPReg> for X86_64WindowsFastcall {
+    const GP_PARAM_REGS: &'static [X86_64GPReg] = &[
+        X86_64GPReg::RCX,
+        X86_64GPReg::RDX,
+        X86_64GPReg::R8,
+        X86_64GPReg::R9,
+    ];
+    const GP_RETURN_REGS: &'static [X86_64GPReg] = &[X86_64GPReg::RAX];
+    const GP_DEFAULT_FREE_REGS: &'static [X86_64GPReg] = &[
+        // The regs we want to use first should be at the end of this vec.
+        // We will use pop to get which reg to use next
+
+        // Don't use stack pionter: X86_64GPReg::RSP,
+        // Don't use frame pointer: X86_64GPReg::RBP,
+
+        // Use callee saved regs last.
+        X86_64GPReg::RBX,
+        X86_64GPReg::RSI,
+        X86_64GPReg::RDI,
+        X86_64GPReg::R12,
+        X86_64GPReg::R13,
+        X86_64GPReg::R14,
+        X86_64GPReg::R15,
+        // Use caller saved regs first.
+        X86_64GPReg::RAX,
+        X86_64GPReg::RCX,
+        X86_64GPReg::RDX,
+        X86_64GPReg::R8,
+        X86_64GPReg::R9,
+        X86_64GPReg::R10,
+        X86_64GPReg::R11,
+    ];
+    const SHADOW_SPACE_SIZE: u8 = 32;
+
+    #[inline(always)]
+    fn callee_saved(reg: &X86_64GPReg) -> bool {
+        matches!(
+            reg,
+            X86_64GPReg::RBX
+                | X86_64GPReg::RBP
+                | X86_64GPReg::RSI
+                | X86_64GPReg::RSP
+                | X86_64GPReg::RDI
+                | X86_64GPReg::R12
+                | X86_64GPReg::R13
+                | X86_64GPReg::R14
+                | X86_64GPReg::R15
+        )
+    }
+
+    #[inline(always)]
+    fn setup_stack<'a>(
+        buf: &mut Vec<'a, u8>,
+        leaf_function: bool,
+        saved_regs: &[X86_64GPReg],
+        requested_stack_size: i32,
+    ) -> Result<i32, String> {
+        x86_64_generic_setup_stack(buf, leaf_function, saved_regs, requested_stack_size)
+    }
+
+    #[inline(always)]
+    fn cleanup_stack<'a>(
+        buf: &mut Vec<'a, u8>,
+        leaf_function: bool,
+        saved_regs: &[X86_64GPReg],
+        aligned_stack_size: i32,
+    ) -> Result<(), String> {
+        x86_64_generic_cleanup_stack(buf, leaf_function, saved_regs, aligned_stack_size)
+    }
+}
+
+#[inline(always)]
+fn x86_64_generic_setup_stack<'a>(
+    buf: &mut Vec<'a, u8>,
+    leaf_function: bool,
+    saved_regs: &[X86_64GPReg],
+    requested_stack_size: i32,
+) -> Result<i32, String> {
+    if !leaf_function {
+        X86_64Assembler::push_reg64(buf, X86_64GPReg::RBP);
+        X86_64Assembler::mov_reg64_reg64(buf, X86_64GPReg::RBP, X86_64GPReg::RSP);
+    }
+    for reg in saved_regs {
+        X86_64Assembler::push_reg64(buf, *reg);
+    }
+
+    // full size is upcast to i64 to make sure we don't overflow here.
+    let full_size = 8 * saved_regs.len() as i64 + requested_stack_size as i64;
+    let alignment = if full_size <= 0 {
+        0
+    } else {
+        full_size % STACK_ALIGNMENT as i64
+    };
+    let offset = if alignment == 0 {
+        0
+    } else {
+        STACK_ALIGNMENT - alignment as u8
+    };
+    if let Some(aligned_stack_size) = requested_stack_size.checked_add(offset as i32) {
+        if aligned_stack_size > 0 {
+            X86_64Assembler::sub_reg64_reg64_imm32(
+                buf,
+                X86_64GPReg::RSP,
+                X86_64GPReg::RSP,
+                aligned_stack_size,
+            );
+            Ok(aligned_stack_size)
+        } else {
+            Ok(0)
+        }
+    } else {
+        Err("Ran out of stack space".to_string())
+    }
+}
+
+#[inline(always)]
+fn x86_64_generic_cleanup_stack<'a>(
+    buf: &mut Vec<'a, u8>,
+    leaf_function: bool,
+    saved_regs: &[X86_64GPReg],
+    aligned_stack_size: i32,
+) -> Result<(), String> {
+    if aligned_stack_size > 0 {
+        X86_64Assembler::add_reg64_reg64_imm32(
+            buf,
+            X86_64GPReg::RSP,
+            X86_64GPReg::RSP,
+            aligned_stack_size,
+        );
+    }
+    for reg in saved_regs.iter().rev() {
+        X86_64Assembler::pop_reg64(buf, *reg);
+    }
+    if !leaf_function {
+        X86_64Assembler::mov_reg64_reg64(buf, X86_64GPReg::RSP, X86_64GPReg::RBP);
+        X86_64Assembler::pop_reg64(buf, X86_64GPReg::RBP);
+    }
+    Ok(())
+}
+
+impl Assembler<X86_64GPReg> for X86_64Assembler {
+    // These functions should map to the raw assembly functions below.
+    // In some cases, that means you can just directly call one of the direct assembly functions.
+    #[inline(always)]
+    fn abs_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, src: X86_64GPReg) {
+        mov_reg64_reg64(buf, dst, src);
+        neg_reg64(buf, dst);
+        cmovl_reg64_reg64(buf, dst, src);
+    }
+    #[inline(always)]
+    fn add_reg64_reg64_imm32<'a>(
+        buf: &mut Vec<'a, u8>,
+        dst: X86_64GPReg,
+        src1: X86_64GPReg,
+        imm32: i32,
+    ) {
+        if dst == src1 {
+            add_reg64_imm32(buf, dst, imm32);
+        } else {
+            mov_reg64_reg64(buf, dst, src1);
+            add_reg64_imm32(buf, dst, imm32);
+        }
+    }
+    #[inline(always)]
+    fn add_reg64_reg64_reg64<'a>(
+        buf: &mut Vec<'a, u8>,
+        dst: X86_64GPReg,
+        src1: X86_64GPReg,
+        src2: X86_64GPReg,
+    ) {
+        if dst == src1 {
+            add_reg64_reg64(buf, dst, src2);
+        } else if dst == src2 {
+            add_reg64_reg64(buf, dst, src1);
+        } else {
+            mov_reg64_reg64(buf, dst, src1);
+            add_reg64_reg64(buf, dst, src2);
+        }
+    }
+    #[inline(always)]
+    fn mov_reg64_imm64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i64) {
+        mov_reg64_imm64(buf, dst, imm);
+    }
+    #[inline(always)]
+    fn mov_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, src: X86_64GPReg) {
+        mov_reg64_reg64(buf, dst, src);
+    }
+    #[inline(always)]
+    fn mov_reg64_stack32<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, offset: i32) {
+        mov_reg64_stack32(buf, dst, offset);
+    }
+    #[inline(always)]
+    fn mov_stack32_reg64<'a>(buf: &mut Vec<'a, u8>, offset: i32, src: X86_64GPReg) {
+        mov_stack32_reg64(buf, offset, src);
+    }
+    #[inline(always)]
+    fn sub_reg64_reg64_imm32<'a>(
+        buf: &mut Vec<'a, u8>,
+        dst: X86_64GPReg,
+        src1: X86_64GPReg,
+        imm32: i32,
+    ) {
+        if dst == src1 {
+            sub_reg64_imm32(buf, dst, imm32);
+        } else {
+            mov_reg64_reg64(buf, dst, src1);
+            sub_reg64_imm32(buf, dst, imm32);
+        }
+    }
+    #[inline(always)]
+    fn ret<'a>(buf: &mut Vec<'a, u8>) {
+        ret(buf);
+    }
+}
+
+impl X86_64Assembler {
+    #[inline(always)]
+    fn pop_reg64<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
+        pop_reg64(buf, reg);
+    }
+
+    #[inline(always)]
+    fn push_reg64<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
+        push_reg64(buf, reg);
+    }
+}
 const REX: u8 = 0x40;
 const REX_W: u8 = REX + 0x8;
 
-fn add_rm_extension(reg: X86_64GPReg, byte: u8) -> u8 {
+#[inline(always)]
+const fn add_rm_extension(reg: X86_64GPReg, byte: u8) -> u8 {
     if reg as u8 > 7 {
         byte + 1
     } else {
@@ -37,11 +338,13 @@ fn add_rm_extension(reg: X86_64GPReg, byte: u8) -> u8 {
     }
 }
 
-fn add_opcode_extension(reg: X86_64GPReg, byte: u8) -> u8 {
+#[inline(always)]
+const fn add_opcode_extension(reg: X86_64GPReg, byte: u8) -> u8 {
     add_rm_extension(reg, byte)
 }
 
-fn add_reg_extension(reg: X86_64GPReg, byte: u8) -> u8 {
+#[inline(always)]
+const fn add_reg_extension(reg: X86_64GPReg, byte: u8) -> u8 {
     if reg as u8 > 7 {
         byte + 4
     } else {
@@ -49,165 +352,6 @@ fn add_reg_extension(reg: X86_64GPReg, byte: u8) -> u8 {
     }
 }
 
-pub struct X86_64Assembler {}
-pub struct X86_64WindowsFastcall {}
-pub struct X86_64SystemV {}
-
-impl CallConv<X86_64GPReg> for X86_64SystemV {
-    fn gp_param_regs() -> &'static [X86_64GPReg] {
-        &[
-            X86_64GPReg::RDI,
-            X86_64GPReg::RSI,
-            X86_64GPReg::RDX,
-            X86_64GPReg::RCX,
-            X86_64GPReg::R8,
-            X86_64GPReg::R9,
-        ]
-    }
-    fn gp_return_regs() -> &'static [X86_64GPReg] {
-        &[X86_64GPReg::RAX, X86_64GPReg::RDX]
-    }
-    fn gp_default_free_regs() -> &'static [X86_64GPReg] {
-        &[
-            // The regs we want to use first should be at the end of this vec.
-            // We will use pop to get which reg to use next
-            // Use callee saved regs last.
-            X86_64GPReg::RBX,
-            // Don't use frame pointer: X86_64GPReg::RBP,
-            X86_64GPReg::R12,
-            X86_64GPReg::R13,
-            X86_64GPReg::R14,
-            X86_64GPReg::R15,
-            // Use caller saved regs first.
-            X86_64GPReg::RAX,
-            X86_64GPReg::RCX,
-            X86_64GPReg::RDX,
-            // Don't use stack pionter: X86_64GPReg::RSP,
-            X86_64GPReg::RSI,
-            X86_64GPReg::RDI,
-            X86_64GPReg::R8,
-            X86_64GPReg::R9,
-            X86_64GPReg::R10,
-            X86_64GPReg::R11,
-        ]
-    }
-    fn caller_saved_regs() -> ImSet<X86_64GPReg> {
-        // TODO: stop using vec! here. I was just have trouble with some errors, but it shouldn't be needed.
-        ImSet::from(vec![
-            X86_64GPReg::RAX,
-            X86_64GPReg::RCX,
-            X86_64GPReg::RDX,
-            X86_64GPReg::RSP,
-            X86_64GPReg::RSI,
-            X86_64GPReg::RDI,
-            X86_64GPReg::R8,
-            X86_64GPReg::R9,
-            X86_64GPReg::R10,
-            X86_64GPReg::R11,
-        ])
-    }
-    fn callee_saved_regs() -> ImSet<X86_64GPReg> {
-        // TODO: stop using vec! here. I was just have trouble with some errors, but it shouldn't be needed.
-        ImSet::from(vec![
-            X86_64GPReg::RBX,
-            X86_64GPReg::RBP,
-            X86_64GPReg::R12,
-            X86_64GPReg::R13,
-            X86_64GPReg::R14,
-            X86_64GPReg::R15,
-        ])
-    }
-    fn stack_pointer() -> X86_64GPReg {
-        X86_64GPReg::RSP
-    }
-    fn frame_pointer() -> X86_64GPReg {
-        X86_64GPReg::RBP
-    }
-    fn shadow_space_size() -> u8 {
-        0
-    }
-    fn red_zone_size() -> u8 {
-        128
-    }
-}
-
-impl CallConv<X86_64GPReg> for X86_64WindowsFastcall {
-    fn gp_param_regs() -> &'static [X86_64GPReg] {
-        &[
-            X86_64GPReg::RCX,
-            X86_64GPReg::RDX,
-            X86_64GPReg::R8,
-            X86_64GPReg::R9,
-        ]
-    }
-    fn gp_return_regs() -> &'static [X86_64GPReg] {
-        &[X86_64GPReg::RAX]
-    }
-    fn gp_default_free_regs() -> &'static [X86_64GPReg] {
-        &[
-            // The regs we want to use first should be at the end of this vec.
-            // We will use pop to get which reg to use next
-            // Use callee saved regs last.
-            X86_64GPReg::RBX,
-            // Don't use frame pointer: X86_64GPReg::RBP,
-            X86_64GPReg::RSI,
-            // Don't use stack pionter: X86_64GPReg::RSP,
-            X86_64GPReg::RDI,
-            X86_64GPReg::R12,
-            X86_64GPReg::R13,
-            X86_64GPReg::R14,
-            X86_64GPReg::R15,
-            // Use caller saved regs first.
-            X86_64GPReg::RAX,
-            X86_64GPReg::RCX,
-            X86_64GPReg::RDX,
-            X86_64GPReg::R8,
-            X86_64GPReg::R9,
-            X86_64GPReg::R10,
-            X86_64GPReg::R11,
-        ]
-    }
-    fn caller_saved_regs() -> ImSet<X86_64GPReg> {
-        // TODO: stop using vec! here. I was just have trouble with some errors, but it shouldn't be needed.
-        ImSet::from(vec![
-            X86_64GPReg::RAX,
-            X86_64GPReg::RCX,
-            X86_64GPReg::RDX,
-            X86_64GPReg::R8,
-            X86_64GPReg::R9,
-            X86_64GPReg::R10,
-            X86_64GPReg::R11,
-        ])
-    }
-    fn callee_saved_regs() -> ImSet<X86_64GPReg> {
-        // TODO: stop using vec! here. I was just have trouble with some errors, but it shouldn't be needed.
-        ImSet::from(vec![
-            X86_64GPReg::RBX,
-            X86_64GPReg::RBP,
-            X86_64GPReg::RSI,
-            X86_64GPReg::RSP,
-            X86_64GPReg::RDI,
-            X86_64GPReg::R12,
-            X86_64GPReg::R13,
-            X86_64GPReg::R14,
-            X86_64GPReg::R15,
-        ])
-    }
-    fn stack_pointer() -> X86_64GPReg {
-        X86_64GPReg::RSP
-    }
-    fn frame_pointer() -> X86_64GPReg {
-        X86_64GPReg::RBP
-    }
-    fn shadow_space_size() -> u8 {
-        32
-    }
-    fn red_zone_size() -> u8 {
-        0
-    }
-}
-
-impl Assembler<X86_64GPReg> for X86_64Assembler {
 // Below here are the functions for all of the assembly instructions.
 // Their names are based on the instruction and operators combined.
 // You should call `buf.reserve()` if you push or extend more than once.
@@ -215,7 +359,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 // Please keep these in alphanumeric order.
 
 /// `ADD r/m64, imm32` -> Add imm32 sign-extended to 64-bits from r/m64.
-    fn add_register64bit_immediate32bit<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i32) {
+#[inline(always)]
+fn add_reg64_imm32<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i32) {
     // This can be optimized if the immediate is 1 byte.
     let rex = add_rm_extension(dst, REX_W);
     let dst_mod = dst as u8 % 8;
@@ -225,11 +370,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `ADD r/m64,r64` -> Add r64 to r/m64.
-    fn add_register64bit_register64bit<'a>(
+#[inline(always)]
-        buf: &mut Vec<'a, u8>,
+fn add_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, src: X86_64GPReg) {
-        dst: X86_64GPReg,
-        src: X86_64GPReg,
-    ) {
     let rex = add_rm_extension(dst, REX_W);
     let rex = add_reg_extension(src, rex);
     let dst_mod = dst as u8 % 8;
@@ -238,11 +380,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `CMOVL r64,r/m64` -> Move if less (SF≠ OF).
-    fn cmovl_register64bit_register64bit<'a>(
+#[inline(always)]
-        buf: &mut Vec<'a, u8>,
+fn cmovl_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, src: X86_64GPReg) {
-        dst: X86_64GPReg,
-        src: X86_64GPReg,
-    ) {
     let rex = add_reg_extension(dst, REX_W);
     let rex = add_rm_extension(src, rex);
     let dst_mod = (dst as u8 % 8) << 3;
@@ -251,7 +390,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `MOV r/m64, imm32` -> Move imm32 sign extended to 64-bits to r/m64.
-    fn mov_register64bit_immediate32bit<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i32) {
+#[inline(always)]
+fn mov_reg64_imm32<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i32) {
     let rex = add_rm_extension(dst, REX_W);
     let dst_mod = dst as u8 % 8;
     buf.reserve(7);
@@ -260,9 +400,10 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `MOV r64, imm64` -> Move imm64 to r64.
-    fn mov_register64bit_immediate64bit<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i64) {
+#[inline(always)]
+fn mov_reg64_imm64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i64) {
     if imm <= i32::MAX as i64 && imm >= i32::MIN as i64 {
-            Self::mov_register64bit_immediate32bit(buf, dst, imm as i32)
+        mov_reg64_imm32(buf, dst, imm as i32)
     } else {
         let rex = add_opcode_extension(dst, REX_W);
         let dst_mod = dst as u8 % 8;
@@ -273,11 +414,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `MOV r/m64,r64` -> Move r64 to r/m64.
-    fn mov_register64bit_register64bit<'a>(
+#[inline(always)]
-        buf: &mut Vec<'a, u8>,
+fn mov_reg64_reg64<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, src: X86_64GPReg) {
-        dst: X86_64GPReg,
-        src: X86_64GPReg,
-    ) {
     let rex = add_rm_extension(dst, REX_W);
     let rex = add_reg_extension(src, rex);
     let dst_mod = dst as u8 % 8;
@@ -286,11 +424,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `MOV r64,r/m64` -> Move r/m64 to r64.
-    fn mov_register64bit_stackoffset32bit<'a>(
+#[inline(always)]
-        buf: &mut Vec<'a, u8>,
+fn mov_reg64_stack32<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, offset: i32) {
-        dst: X86_64GPReg,
-        offset: i32,
-    ) {
     // This can be optimized based on how many bytes the offset actually is.
     // This function can probably be made to take any memory offset, I didn't feel like figuring it out rn.
     // Also, this may technically be faster genration since stack operations should be so common.
@@ -302,11 +437,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `MOV r/m64,r64` -> Move r64 to r/m64.
-    fn mov_stackoffset32bit_register64bit<'a>(
+#[inline(always)]
-        buf: &mut Vec<'a, u8>,
+fn mov_stack32_reg64<'a>(buf: &mut Vec<'a, u8>, offset: i32, src: X86_64GPReg) {
-        offset: i32,
-        src: X86_64GPReg,
-    ) {
     // This can be optimized based on how many bytes the offset actually is.
     // This function can probably be made to take any memory offset, I didn't feel like figuring it out rn.
     // Also, this may technically be faster genration since stack operations should be so common.
@@ -318,19 +450,22 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `NEG r/m64` -> Two's complement negate r/m64.
-    fn neg_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
+#[inline(always)]
+fn neg_reg64<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
     let rex = add_rm_extension(reg, REX_W);
     let reg_mod = reg as u8 % 8;
     buf.extend(&[rex, 0xF7, 0xD8 + reg_mod]);
 }
 
 /// `RET` -> Near return to calling procedure.
+#[inline(always)]
 fn ret<'a>(buf: &mut Vec<'a, u8>) {
     buf.push(0xC3);
 }
 
 /// `SUB r/m64, imm32` -> Subtract imm32 sign-extended to 64-bits from r/m64.
-    fn sub_register64bit_immediate32bit<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i32) {
+#[inline(always)]
+fn sub_reg64_imm32<'a>(buf: &mut Vec<'a, u8>, dst: X86_64GPReg, imm: i32) {
     // This can be optimized if the immediate is 1 byte.
     let rex = add_rm_extension(dst, REX_W);
     let dst_mod = dst as u8 % 8;
@@ -340,7 +475,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `POP r64` -> Pop top of stack into r64; increment stack pointer. Cannot encode 32-bit operand size.
-    fn pop_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
+#[inline(always)]
+fn pop_reg64<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
     let reg_mod = reg as u8 % 8;
     if reg as u8 > 7 {
         let rex = add_opcode_extension(reg, REX);
@@ -351,7 +487,8 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
 }
 
 /// `PUSH r64` -> Push r64,
-    fn push_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
+#[inline(always)]
+fn push_reg64<'a>(buf: &mut Vec<'a, u8>, reg: X86_64GPReg) {
     let reg_mod = reg as u8 % 8;
     if reg as u8 > 7 {
         let rex = add_opcode_extension(reg, REX);
@@ -360,7 +497,6 @@ impl Assembler<X86_64GPReg> for X86_64Assembler {
         buf.push(0x50 + reg_mod);
     }
 }
-}
 
 // When writing tests, it is a good idea to test both a number and unnumbered register.
 // This is because R8-R15 often have special instruction prefixes.
@@ -372,7 +508,7 @@ mod tests {
     const TEST_I64: i64 = 0x12345678_9ABCDEF0;
 
     #[test]
-    fn test_add_register64bit_immediate32bit() {
+    fn test_add_reg64_imm32() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (dst, expected) in &[
@@ -380,14 +516,14 @@ mod tests {
             (X86_64GPReg::R15, [0x49, 0x81, 0xC7]),
         ] {
             buf.clear();
-            X86_64Assembler::add_register64bit_immediate32bit(&mut buf, *dst, TEST_I32);
+            add_reg64_imm32(&mut buf, *dst, TEST_I32);
             assert_eq!(expected, &buf[..3]);
             assert_eq!(TEST_I32.to_le_bytes(), &buf[3..]);
         }
     }
 
     #[test]
-    fn test_add_register64bit_register64bit() {
+    fn test_add_reg64_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for ((dst, src), expected) in &[
@@ -397,13 +533,13 @@ mod tests {
             ((X86_64GPReg::R15, X86_64GPReg::R15), [0x4D, 0x01, 0xFF]),
         ] {
             buf.clear();
-            X86_64Assembler::add_register64bit_register64bit(&mut buf, *dst, *src);
+            add_reg64_reg64(&mut buf, *dst, *src);
             assert_eq!(expected, &buf[..]);
         }
     }
 
     #[test]
-    fn test_cmovl_register64bit_register64bit() {
+    fn test_cmovl_reg64_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for ((dst, src), expected) in &[
@@ -425,13 +561,13 @@ mod tests {
             ),
         ] {
             buf.clear();
-            X86_64Assembler::cmovl_register64bit_register64bit(&mut buf, *dst, *src);
+            cmovl_reg64_reg64(&mut buf, *dst, *src);
             assert_eq!(expected, &buf[..]);
         }
     }
 
     #[test]
-    fn test_mov_register64bit_immediate32bit() {
+    fn test_mov_reg64_imm32() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (dst, expected) in &[
@@ -439,14 +575,14 @@ mod tests {
             (X86_64GPReg::R15, [0x49, 0xC7, 0xC7]),
         ] {
             buf.clear();
-            X86_64Assembler::mov_register64bit_immediate32bit(&mut buf, *dst, TEST_I32);
+            mov_reg64_imm32(&mut buf, *dst, TEST_I32);
             assert_eq!(expected, &buf[..3]);
             assert_eq!(TEST_I32.to_le_bytes(), &buf[3..]);
         }
     }
 
     #[test]
-    fn test_mov_register64bit_immediate64bit() {
+    fn test_mov_reg64_imm64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (dst, expected) in &[
@@ -454,7 +590,7 @@ mod tests {
             (X86_64GPReg::R15, [0x49, 0xBF]),
         ] {
             buf.clear();
-            X86_64Assembler::mov_register64bit_immediate64bit(&mut buf, *dst, TEST_I64);
+            mov_reg64_imm64(&mut buf, *dst, TEST_I64);
             assert_eq!(expected, &buf[..2]);
             assert_eq!(TEST_I64.to_le_bytes(), &buf[2..]);
         }
@@ -463,14 +599,14 @@ mod tests {
             (X86_64GPReg::R15, [0x49, 0xC7, 0xC7]),
         ] {
             buf.clear();
-            X86_64Assembler::mov_register64bit_immediate64bit(&mut buf, *dst, TEST_I32 as i64);
+            mov_reg64_imm64(&mut buf, *dst, TEST_I32 as i64);
             assert_eq!(expected, &buf[..3]);
             assert_eq!(TEST_I32.to_le_bytes(), &buf[3..]);
         }
     }
 
     #[test]
-    fn test_mov_register64bit_register64bit() {
+    fn test_mov_reg64_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for ((dst, src), expected) in &[
@@ -480,13 +616,13 @@ mod tests {
             ((X86_64GPReg::R15, X86_64GPReg::R15), [0x4D, 0x89, 0xFF]),
         ] {
             buf.clear();
-            X86_64Assembler::mov_register64bit_register64bit(&mut buf, *dst, *src);
+            mov_reg64_reg64(&mut buf, *dst, *src);
             assert_eq!(expected, &buf[..]);
         }
     }
 
     #[test]
-    fn test_mov_register64bit_stackoffset32bit() {
+    fn test_mov_reg64_stack32() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for ((dst, offset), expected) in &[
@@ -494,14 +630,14 @@ mod tests {
             ((X86_64GPReg::R15, TEST_I32), [0x4C, 0x8B, 0xBC, 0x24]),
         ] {
             buf.clear();
-            X86_64Assembler::mov_register64bit_stackoffset32bit(&mut buf, *dst, *offset);
+            mov_reg64_stack32(&mut buf, *dst, *offset);
             assert_eq!(expected, &buf[..4]);
             assert_eq!(TEST_I32.to_le_bytes(), &buf[4..]);
         }
     }
 
     #[test]
-    fn test_mov_stackoffset32bit_register64bit() {
+    fn test_mov_stack32_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for ((offset, src), expected) in &[
@@ -509,14 +645,14 @@ mod tests {
             ((TEST_I32, X86_64GPReg::R15), [0x4C, 0x89, 0xBC, 0x24]),
         ] {
             buf.clear();
-            X86_64Assembler::mov_stackoffset32bit_register64bit(&mut buf, *offset, *src);
+            mov_stack32_reg64(&mut buf, *offset, *src);
             assert_eq!(expected, &buf[..4]);
             assert_eq!(TEST_I32.to_le_bytes(), &buf[4..]);
         }
     }
 
     #[test]
-    fn test_neg_register64bit() {
+    fn test_neg_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (reg, expected) in &[
@@ -524,7 +660,7 @@ mod tests {
             (X86_64GPReg::R15, [0x49, 0xF7, 0xDF]),
         ] {
             buf.clear();
-            X86_64Assembler::neg_register64bit(&mut buf, *reg);
+            neg_reg64(&mut buf, *reg);
             assert_eq!(expected, &buf[..]);
         }
     }
@@ -533,12 +669,12 @@ mod tests {
     fn test_ret() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
-        X86_64Assembler::ret(&mut buf);
+        ret(&mut buf);
         assert_eq!(&[0xC3], &buf[..]);
     }
 
     #[test]
-    fn test_sub_register64bit_immediate32bit() {
+    fn test_sub_reg64_imm32() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (dst, expected) in &[
@@ -546,14 +682,14 @@ mod tests {
             (X86_64GPReg::R15, [0x49, 0x81, 0xEF]),
         ] {
             buf.clear();
-            X86_64Assembler::sub_register64bit_immediate32bit(&mut buf, *dst, TEST_I32);
+            sub_reg64_imm32(&mut buf, *dst, TEST_I32);
             assert_eq!(expected, &buf[..3]);
             assert_eq!(TEST_I32.to_le_bytes(), &buf[3..]);
         }
     }
 
     #[test]
-    fn test_pop_register64bit() {
+    fn test_pop_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (dst, expected) in &[
@@ -561,13 +697,13 @@ mod tests {
             (X86_64GPReg::R15, vec![0x41, 0x5F]),
         ] {
             buf.clear();
-            X86_64Assembler::pop_register64bit(&mut buf, *dst);
+            pop_reg64(&mut buf, *dst);
             assert_eq!(&expected[..], &buf[..]);
         }
     }
 
     #[test]
-    fn test_push_register64bit() {
+    fn test_push_reg64() {
         let arena = bumpalo::Bump::new();
         let mut buf = bumpalo::vec![in &arena];
         for (src, expected) in &[
@@ -575,7 +711,7 @@ mod tests {
             (X86_64GPReg::R15, vec![0x41, 0x57]),
         ] {
             buf.clear();
-            X86_64Assembler::push_register64bit(&mut buf, *src);
+            push_reg64(&mut buf, *src);
             assert_eq!(&expected[..], &buf[..]);
         }
     }

compiler/gen_dev/src/object_builder.rs

@@ -1,4 +1,4 @@
-use crate::generic64::{x86_64, Backend64Bit};
+use crate::generic64::{aarch64, x86_64, Backend64Bit};
 use crate::{Backend, Env, Relocation, INLINED_SYMBOLS};
 use bumpalo::collections::Vec;
 use object::write;
@@ -22,7 +22,7 @@ pub fn build_module<'a>(
     target: &Triple,
     procedures: MutMap<(symbol::Symbol, Layout<'a>), Proc<'a>>,
 ) -> Result<Object, String> {
-    let (mut output, mut backend) = match target {
+    match target {
         Triple {
             architecture: TargetArch::X86_64,
             binary_format: TargetBF::Elf,
@@ -33,15 +33,42 @@ pub fn build_module<'a>(
                 x86_64::X86_64Assembler,
                 x86_64::X86_64SystemV,
             > = Backend::new(env, target)?;
-            Ok((
+            build_object(
-                Object::new(BinaryFormat::Elf, Architecture::X86_64, Endianness::Little),
+                env,
+                procedures,
                 backend,
-            ))
+                Object::new(BinaryFormat::Elf, Architecture::X86_64, Endianness::Little),
+            )
+        }
+        Triple {
+            architecture: TargetArch::Aarch64(_),
+            binary_format: TargetBF::Elf,
+            ..
+        } => {
+            let backend: Backend64Bit<
+                aarch64::AArch64GPReg,
+                aarch64::AArch64Assembler,
+                aarch64::AArch64Call,
+            > = Backend::new(env, target)?;
+            build_object(
+                env,
+                procedures,
+                backend,
+                Object::new(BinaryFormat::Elf, Architecture::Aarch64, Endianness::Little),
+            )
         }
         x => Err(format! {
         "the target, {:?}, is not yet implemented",
         x}),
-    }?;
+    }
+}
+
+fn build_object<'a, B: Backend<'a>>(
+    env: &'a Env,
+    procedures: MutMap<(symbol::Symbol, Layout<'a>), Proc<'a>>,
+    mut backend: B,
+    mut output: Object,
+) -> Result<Object, String> {
     let text = output.section_id(StandardSection::Text);
     let data_section = output.section_id(StandardSection::Data);
     let comment = output.add_section(vec![], b"comment".to_vec(), SectionKind::OtherString);

compiler/gen_dev/tests/gen_num.rs

@@ -9,7 +9,7 @@ extern crate libc;
 #[macro_use]
 mod helpers;
 
-#[cfg(all(test, target_os = "linux", target_arch = "x86_64"))]
+#[cfg(all(test, target_os = "linux", any(target_arch = "x86_64"/*, target_arch = "aarch64"*/)))]
 mod gen_num {
     //use roc_std::RocOrder;
 

compiler/module/src/low_level.rs

@@ -6,8 +6,10 @@ pub enum LowLevel {
     StrConcat,
     StrIsEmpty,
     StrStartsWith,
+    StrEndsWith,
     StrSplit,
     StrCountGraphemes,
+    StrFromInt,
     ListLen,
     ListGetUnsafe,
     ListSet,

compiler/module/src/symbol.rs

@@ -673,6 +673,8 @@ define_builtins! {
         5 STR_SPLIT: "split"
         6 STR_COUNT_GRAPHEMES: "countGraphemes"
         7 STR_STARTS_WITH: "startsWith"
+        8 STR_ENDS_WITH: "endsWith"
+        9 STR_FROM_INT: "fromInt"
     }
     4 LIST: "List" => {
         0 LIST_LIST: "List" imported // the List.List type alias

compiler/mono/src/borrow.rs

@@ -547,6 +547,7 @@ pub fn lowlevel_borrow_signature(arena: &Bump, op: LowLevel) -> &[bool] {
         | NumToFloat | Not | NumIsFinite | NumAtan | NumAcos | NumAsin => {
             arena.alloc_slice_copy(&[irrelevant])
         }
-        StrStartsWith => arena.alloc_slice_copy(&[owned, borrowed]),
+        StrStartsWith | StrEndsWith => arena.alloc_slice_copy(&[owned, borrowed]),
+        StrFromInt => arena.alloc_slice_copy(&[irrelevant]),
     }
 }

compiler/mono/src/layout.rs

@@ -460,7 +460,7 @@ impl<'a> Layout<'a> {
 
     pub fn is_refcounted(&self) -> bool {
         match self {
-            Layout::Builtin(Builtin::List(_, _)) => true,
+            Layout::Builtin(Builtin::List(MemoryMode::Refcounted, _)) => true,
             Layout::Builtin(Builtin::Str) => true,
             Layout::RecursiveUnion(_) => true,
             Layout::RecursivePointer => true,
@@ -477,12 +477,12 @@ impl<'a> Layout<'a> {
         match self {
             Builtin(builtin) => builtin.is_refcounted(),
             PhantomEmptyStruct => false,
-            Struct(fields) => fields.iter().any(|f| f.is_refcounted()),
+            Struct(fields) => fields.iter().any(|f| f.contains_refcounted()),
             Union(fields) => fields
                 .iter()
                 .map(|ls| ls.iter())
                 .flatten()
-                .any(|f| f.is_refcounted()),
+                .any(|f| f.contains_refcounted()),
             RecursiveUnion(_) => true,
             Closure(_, closure_layout, _) => closure_layout.contains_refcounted(),
             FunctionPointer(_, _) | RecursivePointer | Pointer(_) => false,

compiler/parse/src/expr.rs

@@ -917,9 +917,13 @@ fn parse_def_signature<'a>(
 
 fn loc_function_arg<'a>(min_indent: u16) -> impl Parser<'a, Located<Expr<'a>>> {
     skip_first!(
-        // If this is a reserved keyword ("if", "then", "case, "when"), then
+        // If this is a reserved keyword ("if", "then", "case, "when"),
-        // it is not a function argument!
+        // followed by a blank space, then it is not a function argument!
-        not(reserved_keyword()),
+        //
+        // (The space is necessary because otherwise we'll get a false
+        // positive on function arguments beginning with keywords,
+        // e.g. `ifBlah` or `isSomething` will register as `if`/`is` keywords)
+        not(and!(reserved_keyword(), space1(min_indent))),
         // Don't parse operators, because they have a higher precedence than function application.
         // If we encounter one, we're done parsing function args!
         move |arena, state| loc_parse_function_arg(min_indent, arena, state)

compiler/parse/src/parser.rs

@@ -777,24 +777,25 @@ macro_rules! skip_first {
             use $crate::parser::Fail;
 
             let original_attempting = state.attempting;
+            let original_state = state.clone();
 
             match $p1.parse(arena, state) {
                 Ok((_, state)) => match $p2.parse(arena, state) {
                     Ok((out2, state)) => Ok((out2, state)),
-                    Err((fail, state)) => Err((
+                    Err((fail, _)) => Err((
                         Fail {
                             attempting: original_attempting,
                             ..fail
                         },
-                        state,
+                        original_state,
                     )),
                 },
-                Err((fail, state)) => Err((
+                Err((fail, _)) => Err((
                     Fail {
                         attempting: original_attempting,
                         ..fail
                     },
-                    state,
+                    original_state,
                 )),
             }
         }
@@ -810,24 +811,25 @@ macro_rules! skip_second {
             use $crate::parser::Fail;
 
             let original_attempting = state.attempting;
+            let original_state = state.clone();
 
             match $p1.parse(arena, state) {
                 Ok((out1, state)) => match $p2.parse(arena, state) {
                     Ok((_, state)) => Ok((out1, state)),
-                    Err((fail, state)) => Err((
+                    Err((fail, _)) => Err((
                         Fail {
                             attempting: original_attempting,
                             ..fail
                         },
-                        state,
+                        original_state,
                     )),
                 },
-                Err((fail, state)) => Err((
+                Err((fail, _)) => Err((
                     Fail {
                         attempting: original_attempting,
                         ..fail
                     },
-                    state,
+                    original_state,
                 )),
             }
         }

compiler/parse/tests/test_parse.rs

@@ -814,6 +814,71 @@ mod test_parse {
         assert_eq!(Ok(expected), actual);
     }
 
+    #[test]
+    fn var_when() {
+        // Regression test for identifiers beginning with keywords (if/then/else/when/is)
+        let arena = Bump::new();
+        let expected = Var {
+            module_name: "",
+            ident: "whenever",
+        };
+        let actual = parse_expr_with(&arena, "whenever");
+
+        assert_eq!(Ok(expected), actual);
+    }
+
+    #[test]
+    fn var_is() {
+        // Regression test for identifiers beginning with keywords (if/then/else/when/is)
+        let arena = Bump::new();
+        let expected = Var {
+            module_name: "",
+            ident: "isnt",
+        };
+        let actual = parse_expr_with(&arena, "isnt");
+
+        assert_eq!(Ok(expected), actual);
+    }
+
+    #[test]
+    fn var_if() {
+        // Regression test for identifiers beginning with keywords (if/then/else/when/is)
+        let arena = Bump::new();
+        let expected = Var {
+            module_name: "",
+            ident: "iffy",
+        };
+        let actual = parse_expr_with(&arena, "iffy");
+
+        assert_eq!(Ok(expected), actual);
+    }
+
+    #[test]
+    fn var_then() {
+        // Regression test for identifiers beginning with keywords (if/then/else/when/is)
+        let arena = Bump::new();
+        let expected = Var {
+            module_name: "",
+            ident: "thenever",
+        };
+        let actual = parse_expr_with(&arena, "thenever");
+
+        assert_eq!(Ok(expected), actual);
+    }
+
+    #[test]
+    fn var_else() {
+        // Regression test for identifiers beginning with keywords (if/then/else/when/is)
+        let arena = Bump::new();
+        let expected = Var {
+            module_name: "",
+            ident: "elsewhere",
+        };
+        let actual = parse_expr_with(&arena, "elsewhere");
+
+        assert_eq!(Ok(expected), actual);
+    }
+
     #[test]
     fn parenthetical_var() {
         let arena = Bump::new();
@@ -1511,6 +1576,32 @@ mod test_parse {
         );
     }
 
+    #[test]
+    fn if_def() {
+        let arena = Bump::new();
+        let newlines = bumpalo::vec![in &arena; Newline, Newline];
+        let def = Def::Body(
+            arena.alloc(Located::new(0, 0, 0, 4, Identifier("iffy"))),
+            arena.alloc(Located::new(0, 0, 5, 6, Num("5"))),
+        );
+        let loc_def = &*arena.alloc(Located::new(0, 0, 0, 6, def));
+        let defs = &[loc_def];
+        let ret = Expr::SpaceBefore(arena.alloc(Num("42")), newlines.into_bump_slice());
+        let loc_ret = Located::new(2, 2, 0, 2, ret);
+        let expected = Defs(defs, arena.alloc(loc_ret));
+
+        assert_parses_to(
+            indoc!(
+                r#"
+                    iffy=5
+
+                    42
+                "#
+            ),
+            expected,
+        );
+    }
+
     #[test]
     fn one_spaced_def() {
         let arena = Bump::new();
@@ -2573,6 +2664,41 @@ mod test_parse {
         assert_eq!(Ok(expected), actual);
     }
 
+    #[test]
+    fn repro_keyword_bug() {
+        // Reproducing this bug requires a bizarre set of things to all be true:
+        //
+        // * Must be parsing a *module* def (nested expr defs don't repro this)
+        // * That top-level module def conatins a def inside it
+        // * That inner def is defining a function
+        // * The name of the inner def begins with a keyword (`if`, `then`, `else`, `when`, `is`)
+        //
+        // If all of these are true, then lookups on that def get skipped over by the parser.
+        // If any one of the above is false, then everything works.
+
+        let arena = Bump::new();
+        let src = indoc!(
+            r#"
+                foo = \list ->
+                    isTest = \_ -> 5
+                    List.map list isTest
+            "#
+        );
+        let actual = module_defs()
+            .parse(&arena, State::new(src.as_bytes(), Attempting::Module))
+            .map(|tuple| tuple.0);
+
+        // It should occur twice in the debug output - once for the pattern,
+        // and then again for the lookup.
+        let occurrences = format!("{:?}", actual)
+            .split("isTest")
+            .collect::<std::vec::Vec<_>>()
+            .len()
+            - 1;
+
+        assert_eq!(occurrences, 2);
+    }
+
     #[test]
     fn standalone_module_defs() {
         use roc_parse::ast::Def::*;

editor/Cargo.toml

@@ -23,6 +23,8 @@ roc_solve = { path = "../compiler/solve" }
 roc_mono = { path = "../compiler/mono" }
 roc_load = { path = "../compiler/load" }
 roc_gen = { path = "../compiler/gen" }
+roc_fmt = { path = "../compiler/fmt" }
+
 roc_reporting = { path = "../compiler/reporting" }
  # TODO switch to clap 3.0.0 once it's out. Tried adding clap = "~3.0.0-beta.1" and cargo wouldn't accept it
 im    = "14" # im and im-rc should always have the same version!

editor/src/file.rs

@@ -0,0 +1,97 @@
+use bumpalo::collections::Vec;
+use bumpalo::Bump;
+use roc_fmt::def::fmt_def;
+use roc_fmt::module::fmt_module;
+use roc_parse::ast::{Attempting, Def, Module};
+use roc_parse::module::module_defs;
+use roc_parse::parser;
+use roc_parse::parser::Parser;
+use roc_region::all::Located;
+use std::ffi::OsStr;
+use std::path::Path;
+use std::{fs, io};
+
+#[derive(Debug)]
+pub struct File<'a> {
+    path: &'a Path,
+    module_header: Module<'a>,
+    content: Vec<'a, Located<Def<'a>>>,
+}
+
+#[derive(Debug)]
+pub enum ReadError {
+    Read(std::io::Error),
+    ParseDefs(parser::Fail),
+    ParseHeader(parser::Fail),
+    DoesntHaveRocExtension,
+}
+
+impl<'a> File<'a> {
+    pub fn read(path: &'a Path, arena: &'a Bump) -> Result<File<'a>, ReadError> {
+        if path.extension() != Some(OsStr::new("roc")) {
+            return Err(ReadError::DoesntHaveRocExtension);
+        }
+
+        let bytes = fs::read(path).map_err(ReadError::Read)?;
+
+        let allocation = arena.alloc(bytes);
+
+        let module_parse_state = parser::State::new(allocation, Attempting::Module);
+        let parsed_module = roc_parse::module::header().parse(&arena, module_parse_state);
+
+        match parsed_module {
+            Ok((module, state)) => {
+                let parsed_defs = module_defs().parse(&arena, state);
+
+                match parsed_defs {
+                    Ok((defs, _)) => Ok(File {
+                        path,
+                        module_header: module,
+                        content: defs,
+                    }),
+                    Err((error, _)) => Err(ReadError::ParseDefs(error)),
+                }
+            }
+            Err((error, _)) => Err(ReadError::ParseHeader(error)),
+        }
+    }
+
+    pub fn fmt(&self) -> String {
+        let arena = Bump::new();
+        let mut formatted_file = String::new();
+
+        let mut module_header_buf = bumpalo::collections::String::new_in(&arena);
+        fmt_module(&mut module_header_buf, &self.module_header);
+
+        formatted_file.push_str(module_header_buf.as_str());
+
+        for def in &self.content {
+            let mut def_buf = bumpalo::collections::String::new_in(&arena);
+
+            fmt_def(&mut def_buf, &def.value, 0);
+
+            formatted_file.push_str(def_buf.as_str());
+        }
+
+        formatted_file
+    }
+
+    pub fn fmt_then_write_to(&self, write_path: &'a Path) -> io::Result<()> {
+        let formatted_file = self.fmt();
+
+        fs::write(write_path, formatted_file)
+    }
+
+    pub fn fmt_then_write_with_name(&self, new_name: &str) -> io::Result<()> {
+        self.fmt_then_write_to(
+            self.path
+                .with_file_name(new_name)
+                .with_extension("roc")
+                .as_path(),
+        )
+    }
+
+    pub fn fmt_then_write(&self) -> io::Result<()> {
+        self.fmt_then_write_to(self.path)
+    }
+}

editor/src/lib.rs

@@ -25,6 +25,7 @@ use winit::event::{ElementState, Event, ModifiersState, VirtualKeyCode};
 use winit::event_loop::ControlFlow;
 
 pub mod ast;
+pub mod file;
 mod rect;
 pub mod text_state;
 mod vertex;

editor/tests/modules/Simple.roc

@@ -0,0 +1,26 @@
+interface Simple
+    exposes [
+    v, x
+     ]
+    imports       []
+
+
+
+
+
+
+
+
+
+v :      Str
+
+
+
+
+
+v = "Value!"
+
+
+
+x : Int
+x = 4

editor/tests/modules/Storage.roc

@@ -0,0 +1,68 @@
+interface Storage
+    exposes [
+        Storage,
+        decoder,
+        get,
+        listener,
+        set
+    ]
+    imports [
+        Map.{ Map },
+        Json.Decode.{ Decoder } as Decode
+        Json.Encode as Encode
+        Ports.FromJs as FromJs
+        Ports.ToJs as ToJs
+    ]
+
+
+################################################################################
+## TYPES ##
+################################################################################
+
+
+Storage : [
+    @Storage (Map Str Decode.Value)
+]
+
+
+################################################################################
+## API ##
+################################################################################
+
+
+get : Storage, Str, Decoder a -> [ Ok a, NotInStorage, DecodeError Decode.Error ]*
+get = \key, decoder, @Storage map ->
+    when Map.get map key is
+        Ok json ->
+            Decode.decodeValue decoder json
+
+        Err NotFound ->
+            NotInStorage
+
+
+set : Encode.Value, Str -> Effect {}
+set json str =
+    ToJs.type "setStorage"
+        |> ToJs.setFields [
+            Field "key" (Encode.str str),
+            Field "value" json
+        ]
+        |> ToJs.send
+
+
+decoder : Decoder Storage
+decoder =
+    Decode.mapType Decode.value
+        |> Decode.map \map -> @Storage map
+
+
+################################################################################
+## PORTS INCOMING ##
+################################################################################
+
+
+listener : (Storage -> msg) -> FromJs.Listener msg
+listener toMsg =
+    FromJs.listen "storageUpdated"
+        (Decode.map decoder toMsg)
+

editor/tests/test_file.rs

@@ -0,0 +1,40 @@
+#[macro_use]
+extern crate pretty_assertions;
+#[macro_use]
+extern crate indoc;
+
+#[cfg(test)]
+mod test_file {
+    use bumpalo::Bump;
+    use roc_editor::file::File;
+    use std::path::Path;
+
+    #[test]
+    fn read_and_fmt_simple_roc_module() {
+        let simple_module_path = Path::new("./tests/modules/Simple.roc");
+
+        let arena = Bump::new();
+
+        let file = File::read(simple_module_path, &arena)
+            .expect("Could not read Simple.roc in test_file test");
+
+        assert_eq!(
+            file.fmt(),
+            indoc!(
+                r#"
+                    interface Simple
+                        exposes [ 
+                        v, x
+                         ]
+                        imports []
+    
+                    v : Str
+                    
+                    v = "Value!"
+
+                    x : Int
+                    x = 4"#
+            )
+        );
+    }
+}

examples/effect/Main.roc

@@ -4,7 +4,7 @@ app "effect-example" imports [ Effect ] provides [ main ] to "./platform"
 main : Effect.Effect {} as Fx
 main =
     when if 1 == 1 then True 3 else False 3.14 is
-        True 3 -> Effect.putLine "Yay"
+        True n -> Effect.putLine (Str.fromInt n)
         _ -> Effect.putLine "Yay"
 
 # main : Effect.Effect {} as Fx

shell.nix

@@ -15,13 +15,15 @@ in with {
   }) { };
 
   isMacOS = currentOS == "darwin";
+  isLinux = currentOS == "linux";
   isAarch64 = currentArch == "aarch64";
 };
 
 with (pkgs);
 
 let
-  darwin-frameworks = if isMacOS then
+  darwin-inputs =
+    if isMacOS then
       with pkgs.darwin.apple_sdk.frameworks; [
         AppKit
         CoreFoundation
@@ -34,7 +36,9 @@ let
     else
       [ ];
 
-  linux-only = if !isMacOS then [
+  linux-inputs =
+    if isLinux then
+      [
         vulkan-headers
         vulkan-loader
         vulkan-tools
@@ -43,9 +47,17 @@ let
         xorg.libXcursor
         xorg.libXrandr
         xorg.libXi
-  ] else
+      ]
+    else
       [ ];
 
+  nixos-env =
+    if isLinux && builtins.pathExists /etc/nixos/configuration.nix then
+      { XDG_DATA_DIRS = "/run/opengl-driver/share:$XDG_DATA_DIRS";
+      }
+    else
+      { };
+
   llvmPkgs = pkgs.llvmPackages_10;
   zig = import ./nix/zig.nix { inherit pkgs isMacOS isAarch64; };
   inputs = [
@@ -77,17 +89,18 @@ let
     ccls
   ];
 
-in mkShell {
+in mkShell (nixos-env // {
-  buildInputs = inputs ++ darwin-frameworks ++ linux-only;
+  buildInputs = inputs ++ darwin-inputs ++ linux-inputs;
-  LLVM_SYS_100_PREFIX = "${llvmPkgs.llvm}";
 
+  # Additional Env vars
+  LLVM_SYS_100_PREFIX = "${llvmPkgs.llvm}";
   APPEND_LIBRARY_PATH = stdenv.lib.makeLibraryPath
-    ([ pkg-config llvmPkgs.libcxx llvmPkgs.libcxxabi libunwind ] ++ linux-only);
+    ([ pkg-config llvmPkgs.libcxx llvmPkgs.libcxxabi libunwind ] ++ linux-inputs);
+  LD_LIBRARY_PATH = "$LD_LIBRARY_PATH:$APPEND_LIBRARY_PATH";
 
   # Aliases don't work cross shell, so we do this
   shellHook = ''
-    export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$APPEND_LIBRARY_PATH"
     export PATH="$PATH:$PWD/nix/bin"
   '';
-}
+})