Explicitly use large code models in AArch64 code gen

This appears to be necessary to compile our programs on AArch64 boxes.
My guess is special-cased code due to PIEs for large code models in
LLVM's codebase but I really have no idea.

compiler/build/src/link.rs

@@ -1072,7 +1072,7 @@ pub fn module_to_dylib(
     opt_level: OptLevel,
 ) -> Result<Library, Error> {
     use crate::target::{self, convert_opt_level};
-    use inkwell::targets::{CodeModel, FileType, RelocMode};
+    use inkwell::targets::{FileType, RelocMode};
 
     let dir = tempfile::tempdir().unwrap();
     let filename = PathBuf::from("Test.roc");
@@ -1083,9 +1083,8 @@ pub fn module_to_dylib(
 
     // Emit the .o file using position-independent code (PIC) - needed for dylibs
     let reloc = RelocMode::PIC;
-    let model = CodeModel::Default;
     let target_machine =
-        target::target_machine(target, convert_opt_level(opt_level), reloc, model).unwrap();
+        target::target_machine(target, convert_opt_level(opt_level), reloc).unwrap();
 
     target_machine
         .write_to_file(module, FileType::Object, &app_o_file)

compiler/build/src/program.rs

@@ -249,7 +249,7 @@ pub fn gen_from_mono_module_llvm(
     use inkwell::attributes::{Attribute, AttributeLoc};
     use inkwell::context::Context;
     use inkwell::module::Linkage;
-    use inkwell::targets::{CodeModel, FileType, RelocMode};
+    use inkwell::targets::{FileType, RelocMode};
 
     let code_gen_start = SystemTime::now();
 
@@ -437,10 +437,8 @@ pub fn gen_from_mono_module_llvm(
         match target.architecture {
             Architecture::X86_64 | Architecture::X86_32(_) | Architecture::Aarch64(_) => {
                 let reloc = RelocMode::PIC;
-                let model = CodeModel::Default;
                 let target_machine =
-                    target::target_machine(target, convert_opt_level(opt_level), reloc, model)
+                    target::target_machine(target, convert_opt_level(opt_level), reloc).unwrap();
-                        .unwrap();
 
                 target_machine
                     .write_to_file(env.module, FileType::Object, app_o_file)

compiler/build/src/target.rs

@@ -147,19 +147,28 @@ pub fn target_machine(
     target: &Triple,
     opt: OptimizationLevel,
     reloc: RelocMode,
-    model: CodeModel,
 ) -> Option<TargetMachine> {
     let arch = arch_str(target);
 
     init_arch(target);
 
+    let code_model = match target.architecture {
+        // LLVM 12 will not compile our programs without a large code model.
+        // The reason is not totally clear to me, but my guess is a few special-cases in
+        //   llvm/lib/Target/AArch64/AArch64ISelLowering.cpp (instructions)
+        //   llvm/lib/Target/AArch64/AArch64Subtarget.cpp (GoT tables)
+        // Revisit when upgrading to LLVM 13.
+        Architecture::Aarch64(..) => CodeModel::Large,
+        _ => CodeModel::Default,
+    };
+
     Target::from_name(arch).unwrap().create_target_machine(
         &TargetTriple::create(target_triple_str(target)),
         "generic",
         "", // TODO: this probably should be TargetMachine::get_host_cpu_features() to enable all features.
         opt,
         reloc,
-        model,
+        code_model,
     )
 }