Add unit tagging to CppOverloadSetId (#6212)

No update to lldbinit.py because we don't currently have
dumping/debugging support for CppOverloadSetId anyway.

toolchain/check/testdata/basics/raw_sem_ir/cpp_interop.carbon

@@ -135,9 +135,9 @@ fn G(x: Cpp.X) {
 // CHECK:STDOUT:     inst60000022:    {kind: CompleteTypeWitness, arg0: inst60000020, type: type(inst(WitnessType))}
 // CHECK:STDOUT:     inst60000023:    {kind: PointerType, arg0: inst60000020, type: type(TypeType)}
 // CHECK:STDOUT:     inst60000024:    {kind: NameRef, arg0: name0, arg1: inst60000010, type: type(inst(NamespaceType))}
-// CHECK:STDOUT:     inst60000025:    {kind: CppOverloadSetType, arg0: cpp_overload_set0, arg1: specific<none>, type: type(TypeType)}
-// CHECK:STDOUT:     inst60000026:    {kind: CppOverloadSetValue, arg0: cpp_overload_set0, type: type(inst60000025)}
-// CHECK:STDOUT:     inst60000027:    {kind: CppOverloadSetValue, arg0: cpp_overload_set0, type: type(inst60000025)}
+// CHECK:STDOUT:     inst60000025:    {kind: CppOverloadSetType, arg0: cpp_overload_set60000000, arg1: specific<none>, type: type(TypeType)}
+// CHECK:STDOUT:     inst60000026:    {kind: CppOverloadSetValue, arg0: cpp_overload_set60000000, type: type(inst60000025)}
+// CHECK:STDOUT:     inst60000027:    {kind: CppOverloadSetValue, arg0: cpp_overload_set60000000, type: type(inst60000025)}
 // CHECK:STDOUT:     inst60000028:    {kind: NameRef, arg0: name4, arg1: inst60000026, type: type(inst60000025)}
 // CHECK:STDOUT:     inst60000029:    {kind: FunctionDecl, arg0: function1, arg1: inst_block_empty, type: type(inst6000002A)}
 // CHECK:STDOUT:     inst6000002A:    {kind: FunctionType, arg0: function1, arg1: specific<none>, type: type(TypeType)}

toolchain/sem_ir/file.cpp

@@ -35,6 +35,7 @@ File::File(const Parse::Tree* parse_tree, CheckIRId check_ir_id,
                                  : LibraryNameId::Default),
       value_stores_(&value_stores),
       filename_(std::move(filename)),
+      cpp_overload_sets_(IdTag(check_ir_id.index, 0)),
       classes_(IdTag(check_ir_id.index, 0)),
       associated_constants_(IdTag(check_ir_id.index, 0)),
       impls_(*this),

toolchain/sem_ir/ids.cpp

@@ -42,6 +42,10 @@ auto ConstantId::Print(llvm::raw_ostream& out, bool disambiguate) const
   }
 }
 
+auto CppOverloadSetId::Print(llvm::raw_ostream& out) const -> void {
+  IdBase::PrintHex(out);
+}
+
 auto CheckIRId::Print(llvm::raw_ostream& out) const -> void {
   if (*this == Cpp) {
     out << Label << "(Cpp)";

toolchain/sem_ir/ids.h

@@ -276,6 +276,8 @@ struct CppOverloadSetId : public IdBase<CppOverloadSetId> {
   static constexpr llvm::StringLiteral Label = "cpp_overload_set";
 
   using IdBase::IdBase;
+
+  auto Print(llvm::raw_ostream& out) const -> void;
 };
 
 // The ID of a function.

toolchain/sem_ir/inst_namer.h

@@ -53,6 +53,8 @@ class InstNamer {
     auto index = id.index;
     if constexpr (std::is_same_v<IdT, ClassId>) {
       index = sem_ir_->classes().GetRawIndex(id);
+    } else if constexpr (std::is_same_v<IdT, CppOverloadSetId>) {
+      index = sem_ir_->cpp_overload_sets().GetRawIndex(id);
     } else if constexpr (std::is_same_v<IdT, AssociatedConstantId>) {
       index = sem_ir_->associated_constants().GetRawIndex(id);
     }