[wasm-gc] Remove rtt type encoding and leftovers

The RTT type can not be used directly in WebAssembly any more and is treated
as a compiler-internal type for the GC MVP.

Bug: v8:7748
Change-Id: I97cb241e6c46446149cc6ae2b1d535b93402fa76
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3787877
Auto-Submit: Matthias Liedtke <mliedtke@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82000}

src/wasm/function-body-decoder-impl.h

@@ -371,49 +371,6 @@ ValueType read_value_type(Decoder* decoder, const byte* pc,
                  ? kWasmBottom
                  : ValueType::RefMaybeNull(heap_type, nullability);
     }
-    // TODO(7748): This is here only for backwards compatibility, and the parsed
-    // depth is ignored.
-    case kRttWithDepthCode:
-    case kRttCode: {
-      if (!VALIDATE(enabled.has_gc())) {
-        DecodeError<validate>(
-            decoder, pc,
-            "invalid value type 'rtt', enable with --experimental-wasm-gc");
-        return kWasmBottom;
-      }
-      if (code == kRttWithDepthCode) {
-        uint32_t depth = decoder->read_u32v<validate>(pc + 1, length, "depth");
-        *length += 1;
-        if (!VALIDATE(depth <= kV8MaxRttSubtypingDepth)) {
-          DecodeError<validate>(
-              decoder, pc,
-              "subtyping depth %u is greater than the maximum depth "
-              "%u supported by V8",
-              depth, kV8MaxRttSubtypingDepth);
-          return kWasmBottom;
-        }
-      }
-      uint32_t type_index_length;
-      uint32_t type_index =
-          decoder->read_u32v<validate>(pc + *length, &type_index_length);
-      *length += type_index_length;
-      if (!VALIDATE(type_index < kV8MaxWasmTypes)) {
-        DecodeError<validate>(
-            decoder, pc,
-            "Type index %u is greater than the maximum number %zu "
-            "of type definitions supported by V8",
-            type_index, kV8MaxWasmTypes);
-        return kWasmBottom;
-      }
-      // We use capacity over size so this works mid-DecodeTypeSection.
-      if (!VALIDATE(module == nullptr ||
-                    type_index < module->types.capacity())) {
-        DecodeError<validate>(decoder, pc, "Type index %u is out of bounds",
-                              type_index);
-        return kWasmBottom;
-      }
-      return ValueType::Rtt(type_index);
-    }
     case kS128Code: {
       if (!VALIDATE(enabled.has_simd())) {
         DecodeError<validate>(

src/wasm/value-type.h

@@ -548,15 +548,15 @@ class ValueType {
           default:
             return kRefCode;
         }
-      case kVoid:
-        return kVoidCode;
-      case kRtt:
-        return kRttCode;
 #define NUMERIC_TYPE_CASE(kind, ...) \
   case k##kind:                      \
     return k##kind##Code;
         FOREACH_NUMERIC_VALUE_TYPE(NUMERIC_TYPE_CASE)
 #undef NUMERIC_TYPE_CASE
+      // The RTT value type can not be used in WebAssembly and is a
+      // compiler-internal type only.
+      case kRtt:
+      case kVoid:
       case kBottom:
         // Unreachable code
         return kVoidCode;

src/wasm/wasm-constants.h

@@ -45,9 +45,6 @@ enum ValueTypeCode : uint8_t {
   kRefNullCode = 0x6c,
   kRefCode = 0x6b,
   kI31RefCode = 0x6a,
-  // TODO(7748): Only here for backwards compatibility, remove when able.
-  kRttWithDepthCode = 0x69,
-  kRttCode = 0x68,
   kDataRefCode = 0x67,
   kArrayRefCode = 0x66,
   kNoneCode = 0x65,

test/unittests/wasm/module-decoder-unittest.cc

@@ -2075,8 +2075,7 @@ TEST_F(WasmModuleVerifyTest, IllegalTableTypes) {
   static Vec table_types[] = {{kRefNullCode, 0},
                               {kRefNullCode, 1},
                               {kRefNullCode, kI31RefCode},
-                              {kI31RefCode},
-                              {kRttCode, 0}};
+                              {kI31RefCode}};
 
   for (Vec type : table_types) {
     Vec data = {