[wasm-gc] Fix/Clarify some TODOs

Functional change: Allow rtts as exception values.
Additional change: Remove liftoff subtyping TODO in anticipation of
removal of full ValueType usage in Liftoff.

Bug: v8:7748
Change-Id: I676a7fa6417d6e86bb148b4f5b9b086cc704928e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2714702Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72973}

src/compiler/wasm-compiler.cc

@@ -2356,11 +2356,11 @@ Node* WasmGraphBuilder::Throw(uint32_t exception_index,
         break;
       case wasm::kRef:
       case wasm::kOptRef:
+      case wasm::kRtt:
+      case wasm::kRttWithDepth:
         STORE_FIXED_ARRAY_SLOT_ANY(values_array, index, value);
         ++index;
         break;
-      case wasm::kRtt:  // TODO(7748): Implement.
-      case wasm::kRttWithDepth:
       case wasm::kI8:
       case wasm::kI16:
       case wasm::kStmt:
@@ -2493,11 +2493,11 @@ Node* WasmGraphBuilder::GetExceptionValues(Node* except_obj,
         break;
       case wasm::kRef:
       case wasm::kOptRef:
+      case wasm::kRtt:
+      case wasm::kRttWithDepth:
         value = LOAD_FIXED_ARRAY_SLOT_ANY(values_array, index);
         ++index;
         break;
-      case wasm::kRtt:  // TODO(7748): Implement.
-      case wasm::kRttWithDepth:
       case wasm::kI8:
       case wasm::kI16:
       case wasm::kStmt:

src/wasm/baseline/liftoff-assembler.cc

@@ -98,7 +98,6 @@ class StackTransferRecipe {
       // edges), we only care that pointer types stay amongst pointer types.
       // It's fine if ref/optref overwrite each other.
       DCHECK(src.is_object_reference_type());
-      // TODO(7748): Check that one type is subtype of the other?
     } else {
       // All other types (primitive numbers, RTTs, bottom/stmt) must be equal.
       DCHECK_EQ(dst, src);

src/wasm/wasm-objects-inl.h

@@ -130,8 +130,7 @@ ACCESSORS(WasmGlobalObject, untagged_buffer, JSArrayBuffer,
           kUntaggedBufferOffset)
 ACCESSORS(WasmGlobalObject, tagged_buffer, FixedArray, kTaggedBufferOffset)
 SMI_ACCESSORS(WasmGlobalObject, offset, kOffsetOffset)
-// TODO(7748): This will not suffice to hold the 32-bit encoding of a ValueType.
-// We need to devise and encoding that does, and also encodes is_mutable.
+// TODO(7748): Try to come up with some encoding that includes is_mutable?
 SMI_ACCESSORS(WasmGlobalObject, raw_type, kRawTypeOffset)
 SMI_ACCESSORS(WasmGlobalObject, is_mutable, kIsMutableOffset)
 

src/wasm/wasm-objects.h

@@ -339,8 +339,8 @@ class WasmGlobalObject : public JSObject {
   DECL_INT32_ACCESSORS(offset)
   DECL_INT_ACCESSORS(raw_type)
   DECL_PRIMITIVE_ACCESSORS(type, wasm::ValueType)
-  // TODO(7748): Once we improve the encoding of mutability/type, turn this back
-  // into a boolean accessor.
+  // TODO(7748): If we encode mutability in raw_type, turn this into a boolean
+  // accessor.
   DECL_INT_ACCESSORS(is_mutable)
 
   // Dispatched behavior.

src/wasm/wasm-subtyping.cc

@@ -258,8 +258,7 @@ bool ArrayIsSubtypeOf(uint32_t subtype_index, uint32_t supertype_index,
   }
 }
 
-// TODO(7748): Expand this with function subtyping once the hiccups
-// with 'exact types' have been cleared.
+// TODO(7748): Expand this with function subtyping when it is introduced.
 bool FunctionIsSubtypeOf(uint32_t subtype_index, uint32_t supertype_index,
                          const WasmModule* sub_module,
                          const WasmModule* super_module) {