Remove the special case for i32. (#4543)

For the few remaining uses of the builtin `i32` type, manually build an
`IntType(Signed, 32)` value instead. These are:

- The return type of `Run`.
- The type that int literals in an `if` expression are converted into.
- The type of an array index expression.

We should consider converting those three cases away from `i32` over
time.

---------

Co-authored-by: Jon Ross-Perkins <[email protected]>

Author: zygoloid

core/prelude/operators/as.carbon

@@ -19,10 +19,6 @@ interface ImplicitAs(Dest:! type) {
 
 // TODO: These impls should live with Core.Int, but currently that's a builtin
 // not a class type, so there is no other library these can go in.
-impl IntLiteral() as ImplicitAs(i32) {
-  fn Convert[self: Self]() -> i32 = "int.convert_checked";
-}
-
 impl forall [N:! IntLiteral()] IntLiteral() as ImplicitAs(Int(N)) {
   fn Convert[self: Self]() -> Int(N) = "int.convert_checked";
 }
@@ -31,10 +27,6 @@ impl forall [N:! IntLiteral()] IntLiteral() as ImplicitAs(UInt(N)) {
   fn Convert[self: Self]() -> UInt(N) = "int.convert_checked";
 }
 
-impl i32 as ImplicitAs(IntLiteral()) {
-  fn Convert[self: Self]() -> IntLiteral() = "int.convert_checked";
-}
-
 impl forall [N:! IntLiteral()] Int(N) as ImplicitAs(IntLiteral()) {
   fn Convert[self: Self]() -> IntLiteral() = "int.convert_checked";
 }
@@ -44,10 +36,6 @@ impl forall [N:! IntLiteral()] UInt(N) as ImplicitAs(IntLiteral()) {
 }
 
 // TODO: Remove these once ImplicitAs extends As.
-impl IntLiteral() as As(i32) {
-  fn Convert[self: Self]() -> i32 = "int.convert_checked";
-}
-
 impl forall [N:! IntLiteral()] IntLiteral() as As(Int(N)) {
   fn Convert[self: Self]() -> Int(N) = "int.convert_checked";
 }
@@ -56,10 +44,6 @@ impl forall [N:! IntLiteral()] IntLiteral() as As(UInt(N)) {
   fn Convert[self: Self]() -> UInt(N) = "int.convert_checked";
 }
 
-impl i32 as As(IntLiteral()) {
-  fn Convert[self: Self]() -> IntLiteral() = "int.convert_checked";
-}
-
 impl forall [N:! IntLiteral()] Int(N) as As(IntLiteral()) {
   fn Convert[self: Self]() -> IntLiteral() = "int.convert_checked";
 }

core/prelude/types.carbon

@@ -12,7 +12,6 @@ export import library "prelude/types/bool";
 // import library "prelude/types/i32";
 
 fn IntLiteral() -> type = "int_literal.make_type";
-fn Int32() -> type = "int.make_type_32";
 fn Int(size: IntLiteral()) -> type = "int.make_type_signed";
 fn UInt(size: IntLiteral()) -> type = "int.make_type_unsigned";
 fn Float(size: IntLiteral()) -> type = "float.make_type";

core/prelude/types/i32.carbon

@@ -4,7 +4,7 @@
 
 package Core library "prelude/types/i32";
 
-// For Int32():
+// For Int():
 import library "prelude/types";
 import library "prelude/operators";
 

toolchain/check/context.cpp

@@ -1010,7 +1010,6 @@ class TypeCompleter {
       case SemIR::BuiltinInstKind::Invalid:
       case SemIR::BuiltinInstKind::BoolType:
       case SemIR::BuiltinInstKind::IntLiteralType:
-      case SemIR::BuiltinInstKind::IntType:
       case SemIR::BuiltinInstKind::FloatType:
       case SemIR::BuiltinInstKind::NamespaceType:
       case SemIR::BuiltinInstKind::BoundMethodType:
@@ -1368,6 +1367,17 @@ auto Context::GetGenericInterfaceType(SemIR::InterfaceId interface_id,
       *this, interface_id, enclosing_specific_id);
 }
 
+auto Context::GetInt32Type() -> SemIR::TypeId {
+  auto bit_width_const_id = TryEvalInst(
+      *this, SemIR::InstId::Invalid,
+      SemIR::IntValue{
+          .type_id = GetBuiltinType(SemIR::BuiltinInstKind::IntLiteralType),
+          .int_id = ints().Add(32)});
+  return GetCompleteTypeImpl<SemIR::IntType>(
+      *this, SemIR::IntKind::Signed,
+      constant_values().GetInstId(bit_width_const_id));
+}
+
 auto Context::GetInterfaceType(SemIR::InterfaceId interface_id,
                                SemIR::SpecificId specific_id) -> SemIR::TypeId {
   return GetTypeImpl<SemIR::FacetType>(

toolchain/check/context.h

@@ -406,6 +406,9 @@ class Context {
                                SemIR::SpecificId enclosing_specific_id)
       -> SemIR::TypeId;
 
+  // Returns the type `i32`.
+  auto GetInt32Type() -> SemIR::TypeId;
+
   // Gets the facet type corresponding to a particular interface.
   auto GetInterfaceType(SemIR::InterfaceId interface_id,
                         SemIR::SpecificId specific_id) -> SemIR::TypeId;

toolchain/check/convert.cpp

@@ -153,9 +153,9 @@ static auto MakeElementAccessInst(Context& context, SemIR::LocId loc_id,
     // index so that we don't need an integer literal instruction here, and
     // remove this special case.
     auto index_id = block.template AddInst<SemIR::IntValue>(
-        loc_id,
-        {.type_id = context.GetBuiltinType(SemIR::BuiltinInstKind::IntType),
-         .int_id = context.ints().AddUnsigned(llvm::APInt(32, i))});
+        loc_id, {.type_id = context.GetBuiltinType(
+                     SemIR::BuiltinInstKind::IntLiteralType),
+                 .int_id = context.ints().Add(static_cast<int64_t>(i))});
     return block.template AddInst<AccessInstT>(
         loc_id, {elem_type_id, aggregate_id, index_id});
   } else {

toolchain/check/eval.cpp

@@ -1057,10 +1057,6 @@ static auto MakeConstantForBuiltinCall(Context& context, SemIRLoc loc,
           SemIR::InstId::BuiltinIntLiteralType);
     }
 
-    case SemIR::BuiltinFunctionKind::IntMakeType32: {
-      return context.constant_values().Get(SemIR::InstId::BuiltinIntType);
-    }
-
     case SemIR::BuiltinFunctionKind::IntMakeTypeSigned: {
       return MakeIntTypeResult(context, loc, SemIR::IntKind::Signed, arg_ids[0],
                                phase);

toolchain/check/handle_function.cpp

@@ -300,8 +300,7 @@ static auto BuildFunctionDecl(Context& context,
         !function_info.param_patterns_id.is_valid() ||
         !context.inst_blocks().Get(function_info.param_patterns_id).empty() ||
         (return_type_id.is_valid() &&
-         return_type_id !=
-             context.GetBuiltinType(SemIR::BuiltinInstKind::IntType) &&
+         return_type_id != context.GetInt32Type() &&
          return_type_id != context.GetTupleType({}))) {
       CARBON_DIAGNOSTIC(InvalidMainRunSignature, Error,
                         "invalid signature for `Main.Run` function; expected "

toolchain/check/handle_if_expr.cpp

@@ -38,9 +38,8 @@ static auto DecayIntLiteralToSizedInt(Context& context, Parse::NodeId node_id,
     -> SemIR::InstId {
   if (context.types().GetInstId(context.insts().Get(operand_id).type_id()) ==
       SemIR::InstId::BuiltinIntLiteralType) {
-    operand_id = ConvertToValueOfType(
-        context, node_id, operand_id,
-        context.GetBuiltinType(SemIR::BuiltinInstKind::IntType));
+    operand_id = ConvertToValueOfType(context, node_id, operand_id,
+                                      context.GetInt32Type());
   }
   return operand_id;
 }

toolchain/check/handle_index.cpp

@@ -133,8 +133,7 @@ auto HandleParseNode(Context& context, Parse::IndexExprId node_id) -> bool {
     case CARBON_KIND(SemIR::ArrayType array_type): {
       auto index_loc_id = context.insts().GetLocId(index_inst_id);
       auto cast_index_id = ConvertToValueOfType(
-          context, index_loc_id, index_inst_id,
-          context.GetBuiltinType(SemIR::BuiltinInstKind::IntType));
+          context, index_loc_id, index_inst_id, context.GetInt32Type());
       auto array_cat =
           SemIR::GetExprCategory(context.sem_ir(), operand_inst_id);
       if (array_cat == SemIR::ExprCategory::Value) {