From db8e135a055c0f71fd80e2533430a4c9304ffd56 Mon Sep 17 00:00:00 2001
From: Ayaz Hafiz <ayaz@rwx.com>
Date: Mon, 7 Nov 2022 15:31:00 -0600
Subject: [PATCH] Simplify AbilitySet storage

---
 crates/compiler/solve/src/solve.rs | 18 +++++++-----------
 crates/compiler/types/src/types.rs | 18 +++++++++++++-----
 2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/crates/compiler/solve/src/solve.rs b/crates/compiler/solve/src/solve.rs
index 6dfb56239f..b42ee50e38 100644
--- a/crates/compiler/solve/src/solve.rs
+++ b/crates/compiler/solve/src/solve.rs
@@ -2819,7 +2819,7 @@ fn type_to_variable<'a>(
                     let lambda_set_vars_offset = type_arguments_offset + type_arguments.len();
                     let infer_ext_vars_offset = lambda_set_vars_offset + lambda_set_variables.len();
 
-                    for (((target_index, arg_type), arg_region), opt_ability) in
+                    for (((target_index, arg_type), arg_region), abilities) in
                         (new_variables.indices().skip(type_arguments_offset))
                             .zip(type_arguments.into_iter())
                             .zip(type_argument_regions.into_iter())
@@ -2827,9 +2827,9 @@ fn type_to_variable<'a>(
                     {
                         let copy_var = helper!(arg_type);
                         subs.variables[target_index] = copy_var;
-                        if types[opt_ability].is_some() {
+                        if !types[abilities].is_empty() {
                             let arg_region = types[arg_region];
-                            bind_to_abilities.push((Loc::at(arg_region, copy_var), opt_ability));
+                            bind_to_abilities.push((Loc::at(arg_region, copy_var), abilities));
                         }
                     }
 
@@ -2917,7 +2917,7 @@ fn type_to_variable<'a>(
 
                     let new_variables = VariableSubsSlice::reserve_into_subs(subs, all_vars_length);
 
-                    for (((target_index, typ), region), opt_abilities) in
+                    for (((target_index, typ), region), abilities) in
                         (new_variables.indices().skip(type_arguments_offset))
                             .zip(type_arguments.into_iter())
                             .zip(type_argument_regions.into_iter())
@@ -2925,9 +2925,9 @@ fn type_to_variable<'a>(
                     {
                         let copy_var = helper!(typ);
                         subs.variables[target_index] = copy_var;
-                        if types[opt_abilities].is_some() {
+                        if !types[abilities].is_empty() {
                             let region = types[region];
-                            bind_to_abilities.push((Loc::at(region, copy_var), opt_abilities));
+                            bind_to_abilities.push((Loc::at(region, copy_var), abilities));
                         }
                     }
 
@@ -3063,11 +3063,7 @@ fn type_to_variable<'a>(
     }
 
     for (Loc { value: var, region }, abilities) in bind_to_abilities {
-        // TODO: SoA represent as Some<Index<AbilitySet>>, not the other way
-        let abilities = types[abilities]
-            .as_ref()
-            .expect("should only have been added if it was Some");
-
+        let abilities = &types[abilities];
         match *subs.get_content_unchecked(var) {
             Content::RigidVar(a) => {
                 // TODO(multi-abilities): check run cache
diff --git a/crates/compiler/types/src/types.rs b/crates/compiler/types/src/types.rs
index dea2a0e16c..feff4e9c23 100644
--- a/crates/compiler/types/src/types.rs
+++ b/crates/compiler/types/src/types.rs
@@ -297,6 +297,10 @@ impl AbilitySet {
     pub fn into_sorted_iter(self) -> impl ExactSizeIterator<Item = Symbol> {
         self.0.into_iter()
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
 }
 
 impl FromIterator<Symbol> for AbilitySet {
@@ -363,7 +367,7 @@ impl std::ops::Neg for Polarity {
 
 pub struct AliasShared {
     pub symbol: Symbol,
-    pub type_argument_abilities: Slice<Option<AbilitySet>>,
+    pub type_argument_abilities: Slice<AbilitySet>,
     pub type_argument_regions: Slice<Region>,
     pub lambda_set_variables: Slice<TypeTag>,
     pub infer_ext_in_output_variables: Slice<TypeTag>,
@@ -468,7 +472,7 @@ pub struct Types {
     field_names: Vec<Lowercase>,
 
     // aliases
-    type_arg_abilities: Vec<Option<AbilitySet>>, // TODO: structural sharing for `AbilitySet`s themselves
+    type_arg_abilities: Vec<AbilitySet>, // TODO: structural sharing for `AbilitySet`s themselves
     aliases: Vec<AliasShared>,
 
     // these tag types are relatively rare, and so we store them in a way that reduces space, at
@@ -650,7 +654,9 @@ impl Types {
 
         let type_argument_abilities = Slice::extend_new(
             &mut self.type_arg_abilities,
-            type_arguments.iter().map(|a| a.opt_abilities.clone()),
+            type_arguments
+                .iter()
+                .map(|a| a.opt_abilities.as_ref().cloned().unwrap_or_default()),
         );
 
         // TODO: populate correctly
@@ -836,7 +842,9 @@ impl Types {
 
                 let type_argument_abilities = Slice::extend_new(
                     &mut self.type_arg_abilities,
-                    type_arguments.iter().map(|a| a.value.opt_abilities.clone()),
+                    type_arguments
+                        .iter()
+                        .map(|a| a.value.opt_abilities.as_ref().cloned().unwrap_or_default()),
                 );
 
                 let alias_shared = AliasShared {
@@ -987,7 +995,7 @@ macro_rules! impl_types_index_slice {
 impl_types_index! {
     tags, TypeTag
     aliases, AliasShared
-    type_arg_abilities, Option<AbilitySet>
+    type_arg_abilities, AbilitySet
     regions, Region
     tag_names, TagName
     field_types, RecordField<()>