Bugfix handle more specialization instances

compiler/mono/src/ir.rs

@@ -770,6 +770,26 @@ impl<'a> Procs<'a> {
             needed_symbol_specializations: BumpMap::new_in(arena),
         }
     }
+
+    /// Expects and removes a single specialization symbol for the given requested symbol.
+    fn remove_single_symbol_specialization(&mut self, symbol: Symbol) -> Option<Symbol> {
+        let mut specialized_symbols = self
+            .needed_symbol_specializations
+            .drain_filter(|(sym, _), _| sym == &symbol);
+
+        let specialization_symbol = specialized_symbols
+            .next()
+            .map(|(_, (_, specialized_symbol))| specialized_symbol);
+
+        debug_assert_eq!(
+            specialized_symbols.count(),
+            0,
+            "Symbol {:?} has multiple specializations",
+            symbol
+        );
+
+        specialization_symbol
+    }
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -2468,11 +2488,11 @@ fn specialize_external<'a>(
                     // An argument from the closure list may have taken on a specialized symbol
                     // name during the evaluation of the def body. If this is the case, load the
                     // specialized name rather than the original captured name!
-                    let get_specialized_name = |symbol, layout| {
+                    let mut get_specialized_name = |symbol, layout| {
                         procs
                             .needed_symbol_specializations
-                            .get(&(symbol, layout))
-                            .map(|(_, specialized)| *specialized)
+                            .remove(&(symbol, layout))
+                            .map(|(_, specialized)| specialized)
                             .unwrap_or(symbol)
                     };
 
@@ -3304,7 +3324,7 @@ pub fn with_hole<'a>(
             } else {
                 // this may be a destructure pattern
                 let (mono_pattern, assignments) =
-                    match from_can_pattern(env, layout_cache, &def.loc_pattern.value) {
+                    match from_can_pattern(env, procs, layout_cache, &def.loc_pattern.value) {
                         Ok(v) => v,
                         Err(_runtime_error) => {
                             // todo
@@ -5492,6 +5512,7 @@ pub fn from_can<'a>(
         }
         LetNonRec(def, cont, outer_annotation) => {
             if let roc_can::pattern::Pattern::Identifier(symbol) = &def.loc_pattern.value {
+                // dbg!(symbol, &def.loc_expr.value);
                 match def.loc_expr.value {
                     roc_can::expr::Expr::Closure(closure_data) => {
                         register_capturing_closure(env, procs, layout_cache, *symbol, closure_data);
@@ -5706,7 +5727,7 @@ pub fn from_can<'a>(
 
             // this may be a destructure pattern
             let (mono_pattern, assignments) =
-                match from_can_pattern(env, layout_cache, &def.loc_pattern.value) {
+                match from_can_pattern(env, procs, layout_cache, &def.loc_pattern.value) {
                     Ok(v) => v,
                     Err(_) => todo!(),
                 };
@@ -5737,8 +5758,22 @@ pub fn from_can<'a>(
 
                 // layer on any default record fields
                 for (symbol, variable, expr) in assignments {
+                    let specialization_symbol = procs
+                        .remove_single_symbol_specialization(symbol)
+                        // Can happen when the symbol was never used under this body, and hence has no
+                        // requested specialization.
+                        .unwrap_or(symbol);
+
                     let hole = env.arena.alloc(stmt);
-                    stmt = with_hole(env, expr, variable, procs, layout_cache, symbol, hole);
+                    stmt = with_hole(
+                        env,
+                        expr,
+                        variable,
+                        procs,
+                        layout_cache,
+                        specialization_symbol,
+                        hole,
+                    );
                 }
 
                 if let roc_can::expr::Expr::Var(outer_symbol) = def.loc_expr.value {
@@ -5772,6 +5807,7 @@ pub fn from_can<'a>(
 
 fn to_opt_branches<'a>(
     env: &mut Env<'a, '_>,
+    procs: &mut Procs<'a>,
     branches: std::vec::Vec<roc_can::expr::WhenBranch>,
     exhaustive_mark: ExhaustiveMark,
     layout_cache: &mut LayoutCache<'a>,
@@ -5798,7 +5834,7 @@ fn to_opt_branches<'a>(
         }
 
         for loc_pattern in when_branch.patterns {
-            match from_can_pattern(env, layout_cache, &loc_pattern.value) {
+            match from_can_pattern(env, procs, layout_cache, &loc_pattern.value) {
                 Ok((mono_pattern, assignments)) => {
                     loc_branches.push((
                         Loc::at(loc_pattern.region, mono_pattern.clone()),
@@ -5876,7 +5912,7 @@ fn from_can_when<'a>(
         // We can't know what to return!
         return Stmt::RuntimeError("Hit a 0-branch when expression");
     }
-    let opt_branches = to_opt_branches(env, branches, exhaustive_mark, layout_cache);
+    let opt_branches = to_opt_branches(env, procs, branches, exhaustive_mark, layout_cache);
 
     let cond_layout =
         return_on_layout_error!(env, layout_cache.from_var(env.arena, cond_var, env.subs));
@@ -6341,7 +6377,15 @@ fn store_pattern_help<'a>(
 
     match can_pat {
         Identifier(symbol) => {
-            substitute_in_exprs(env.arena, &mut stmt, *symbol, outer_symbol);
+            // An identifier in a pattern can define at most one specialization!
+            // Remove any requested specializations for this name now, since this is the definition site.
+            let specialization_symbol = procs
+                .remove_single_symbol_specialization(*symbol)
+                // Can happen when the symbol was never used under this body, and hence has no
+                // requested specialization.
+                .unwrap_or(*symbol);
+
+            substitute_in_exprs(env.arena, &mut stmt, specialization_symbol, outer_symbol);
         }
         Underscore => {
             // do nothing
@@ -6402,7 +6446,18 @@ fn store_pattern_help<'a>(
             for destruct in destructs {
                 match &destruct.typ {
                     DestructType::Required(symbol) => {
-                        substitute_in_exprs(env.arena, &mut stmt, *symbol, outer_symbol);
+                        let specialization_symbol = procs
+                            .remove_single_symbol_specialization(*symbol)
+                            // Can happen when the symbol was never used under this body, and hence has no
+                            // requested specialization.
+                            .unwrap_or(*symbol);
+
+                        substitute_in_exprs(
+                            env.arena,
+                            &mut stmt,
+                            specialization_symbol,
+                            outer_symbol,
+                        );
                     }
                     DestructType::Guard(guard_pattern) => {
                         return store_pattern_help(
@@ -6480,10 +6535,11 @@ fn store_tag_pattern<'a>(
 
         match argument {
             Identifier(symbol) => {
+                // TODO: use procs.remove_single_symbol_specialization
                 let symbol = procs
                     .needed_symbol_specializations
-                    .get(&(*symbol, arg_layout))
-                    .map(|(_, sym)| *sym)
+                    .remove(&(*symbol, arg_layout))
+                    .map(|(_, sym)| sym)
                     .unwrap_or(*symbol);
 
                 // store immediately in the given symbol
@@ -6562,8 +6618,19 @@ fn store_newtype_pattern<'a>(
 
         match argument {
             Identifier(symbol) => {
-                // store immediately in the given symbol
-                stmt = Stmt::Let(*symbol, load, arg_layout, env.arena.alloc(stmt));
+                // store immediately in the given symbol, removing it specialization if it had any
+                let specialization_symbol = procs
+                    .remove_single_symbol_specialization(*symbol)
+                    // Can happen when the symbol was never used under this body, and hence has no
+                    // requested specialization.
+                    .unwrap_or(*symbol);
+
+                stmt = Stmt::Let(
+                    specialization_symbol,
+                    load,
+                    arg_layout,
+                    env.arena.alloc(stmt),
+                );
                 is_productive = true;
             }
             Underscore => {
@@ -6625,11 +6692,35 @@ fn store_record_destruct<'a>(
 
     match &destruct.typ {
         DestructType::Required(symbol) => {
-            stmt = Stmt::Let(*symbol, load, destruct.layout, env.arena.alloc(stmt));
+            // A destructure can define at most one specialization!
+            // Remove any requested specializations for this name now, since this is the definition site.
+            let specialization_symbol = procs
+                .remove_single_symbol_specialization(*symbol)
+                // Can happen when the symbol was never used under this body, and hence has no
+                // requested specialization.
+                .unwrap_or(*symbol);
+
+            stmt = Stmt::Let(
+                specialization_symbol,
+                load,
+                destruct.layout,
+                env.arena.alloc(stmt),
+            );
         }
         DestructType::Guard(guard_pattern) => match &guard_pattern {
             Identifier(symbol) => {
-                stmt = Stmt::Let(*symbol, load, destruct.layout, env.arena.alloc(stmt));
+                let specialization_symbol = procs
+                    .remove_single_symbol_specialization(*symbol)
+                    // Can happen when the symbol was never used under this body, and hence has no
+                    // requested specialization.
+                    .unwrap_or(*symbol);
+
+                stmt = Stmt::Let(
+                    specialization_symbol,
+                    load,
+                    destruct.layout,
+                    env.arena.alloc(stmt),
+                );
             }
             Underscore => {
                 // important that this is special-cased to do nothing: mono record patterns will extract all the
@@ -6816,48 +6907,53 @@ where
         return build_rest(env, procs, layout_cache);
     }
 
-    // Otherwise we're dealing with an alias to something that doesn't need to be specialized, or
-    // whose usages will already be specialized in the rest of the program.
-    if procs.is_imported_module_thunk(right) {
+    if procs.partial_procs.contains_key(right) {
+        // This is an alias to a function defined in this module.
+        // Attach the alias, then build the rest of the module, so that we reference and specialize
+        // the correct proc.
+        procs.partial_procs.insert_alias(left, right);
+        return build_rest(env, procs, layout_cache);
+    }
+
+    // Otherwise we're dealing with an alias whose usages will tell us what specializations we
+    // need. So let's figure those out first.
     let result = build_rest(env, procs, layout_cache);
 
+    // The specializations we wanted of the symbol on the LHS of this alias.
+    let needed_specializations_of_left = procs
+        .needed_symbol_specializations
+        .drain_filter(|(s, _), _| s == &left)
+        .collect::<std::vec::Vec<_>>();
+
+    if procs.is_imported_module_thunk(right) {
         // if this is an imported symbol, then we must make sure it is
         // specialized, and wrap the original in a function pointer.
+        let mut result = result;
+        for (_, (variable, left)) in needed_specializations_of_left.into_iter() {
             add_needed_external(procs, env, variable, right);
 
             let res_layout = layout_cache.from_var(env.arena, variable, env.subs);
             let layout = return_on_layout_error!(env, res_layout);
 
-        force_thunk(env, right, layout, left, env.arena.alloc(result))
+            result = force_thunk(env, right, layout, left, env.arena.alloc(result));
+        }
+        result
     } else if env.is_imported_symbol(right) {
-        let result = build_rest(env, procs, layout_cache);
-
         // if this is an imported symbol, then we must make sure it is
         // specialized, and wrap the original in a function pointer.
         add_needed_external(procs, env, variable, right);
 
         // then we must construct its closure; since imported symbols have no closure, we use the empty struct
         let_empty_struct(left, env.arena.alloc(result))
-    } else if procs.partial_procs.contains_key(right) {
-        // This is an alias to a function defined in this module.
-        // Attach the alias, then build the rest of the module, so that we reference and specialize
-        // the correct proc.
-        procs.partial_procs.insert_alias(left, right);
-        build_rest(env, procs, layout_cache)
     } else {
-        // This should be a fully specialized value. Replace the alias with the original symbol.
-        let mut result = build_rest(env, procs, layout_cache);
-
         // We need to lift all specializations of "left" to be specializations of "right".
-        let to_update = procs
-            .needed_symbol_specializations
-            .drain_filter(|(s, _), _| s == &left)
-            .collect::<std::vec::Vec<_>>();
         let mut scratchpad_update_specializations = std::vec::Vec::new();
 
-        let left_had_specialization_symbols = !to_update.is_empty();
+        let left_had_specialization_symbols = !needed_specializations_of_left.is_empty();
 
-        for ((_, layout), (specialized_var, specialized_sym)) in to_update.into_iter() {
+        for ((_, layout), (specialized_var, specialized_sym)) in
+            needed_specializations_of_left.into_iter()
+        {
             let old_specialized_sym = procs
                 .needed_symbol_specializations
                 .insert((right, layout), (specialized_var, specialized_sym));
@@ -6867,6 +6963,7 @@ where
             }
         }
 
+        let mut result = result;
         if left_had_specialization_symbols {
             // If the symbol is specialized, only the specializations need to be updated.
             for (old_specialized_sym, specialized_sym) in
@@ -7894,6 +7991,7 @@ pub struct WhenBranch<'a> {
 #[allow(clippy::type_complexity)]
 fn from_can_pattern<'a>(
     env: &mut Env<'a, '_>,
+    procs: &mut Procs<'a>,
     layout_cache: &mut LayoutCache<'a>,
     can_pattern: &roc_can::pattern::Pattern,
 ) -> Result<
@@ -7904,13 +8002,14 @@ fn from_can_pattern<'a>(
     RuntimeError,
 > {
     let mut assignments = Vec::new_in(env.arena);
-    let pattern = from_can_pattern_help(env, layout_cache, can_pattern, &mut assignments)?;
+    let pattern = from_can_pattern_help(env, procs, layout_cache, can_pattern, &mut assignments)?;
 
     Ok((pattern, assignments))
 }
 
 fn from_can_pattern_help<'a>(
     env: &mut Env<'a, '_>,
+    procs: &mut Procs<'a>,
     layout_cache: &mut LayoutCache<'a>,
     can_pattern: &roc_can::pattern::Pattern,
     assignments: &mut Vec<'a, (Symbol, Variable, roc_can::expr::Expr)>,
@@ -8105,7 +8204,13 @@ fn from_can_pattern_help<'a>(
                     let mut mono_args = Vec::with_capacity_in(arguments.len(), env.arena);
                     for ((_, loc_pat), layout) in arguments.iter().zip(field_layouts.iter()) {
                         mono_args.push((
-                            from_can_pattern_help(env, layout_cache, &loc_pat.value, assignments)?,
+                            from_can_pattern_help(
+                                env,
+                                procs,
+                                layout_cache,
+                                &loc_pat.value,
+                                assignments,
+                            )?,
                             *layout,
                         ));
                     }
@@ -8183,6 +8288,7 @@ fn from_can_pattern_help<'a>(
                                 mono_args.push((
                                     from_can_pattern_help(
                                         env,
+                                        procs,
                                         layout_cache,
                                         &loc_pat.value,
                                         assignments,
@@ -8228,6 +8334,7 @@ fn from_can_pattern_help<'a>(
                                 mono_args.push((
                                     from_can_pattern_help(
                                         env,
+                                        procs,
                                         layout_cache,
                                         &loc_pat.value,
                                         assignments,
@@ -8271,6 +8378,7 @@ fn from_can_pattern_help<'a>(
                                 mono_args.push((
                                     from_can_pattern_help(
                                         env,
+                                        procs,
                                         layout_cache,
                                         &loc_pat.value,
                                         assignments,
@@ -8344,6 +8452,7 @@ fn from_can_pattern_help<'a>(
                                 mono_args.push((
                                     from_can_pattern_help(
                                         env,
+                                        procs,
                                         layout_cache,
                                         &loc_pat.value,
                                         assignments,
@@ -8400,6 +8509,7 @@ fn from_can_pattern_help<'a>(
                                 mono_args.push((
                                     from_can_pattern_help(
                                         env,
+                                        procs,
                                         layout_cache,
                                         &loc_pat.value,
                                         assignments,
@@ -8430,8 +8540,13 @@ fn from_can_pattern_help<'a>(
             let arg_layout = layout_cache
                 .from_var(env.arena, *arg_var, env.subs)
                 .unwrap();
-            let mono_arg_pattern =
-                from_can_pattern_help(env, layout_cache, &loc_arg_pattern.value, assignments)?;
+            let mono_arg_pattern = from_can_pattern_help(
+                env,
+                procs,
+                layout_cache,
+                &loc_arg_pattern.value,
+                assignments,
+            )?;
             Ok(Pattern::OpaqueUnwrap {
                 opaque: *opaque,
                 argument: Box::new((mono_arg_pattern, arg_layout)),
@@ -8474,6 +8589,7 @@ fn from_can_pattern_help<'a>(
                                 // this field is destructured by the pattern
                                 mono_destructs.push(from_can_record_destruct(
                                     env,
+                                    procs,
                                     layout_cache,
                                     &destruct.value,
                                     field_layout,
@@ -8565,6 +8681,7 @@ fn from_can_pattern_help<'a>(
 
 fn from_can_record_destruct<'a>(
     env: &mut Env<'a, '_>,
+    procs: &mut Procs<'a>,
     layout_cache: &mut LayoutCache<'a>,
     can_rd: &roc_can::pattern::RecordDestruct,
     field_layout: Layout<'a>,
@@ -8581,7 +8698,7 @@ fn from_can_record_destruct<'a>(
                 DestructType::Required(can_rd.symbol)
             }
             roc_can::pattern::DestructType::Guard(_, loc_pattern) => DestructType::Guard(
-                from_can_pattern_help(env, layout_cache, &loc_pattern.value, assignments)?,
+                from_can_pattern_help(env, procs, layout_cache, &loc_pattern.value, assignments)?,
             ),
         },
     })