[wasm] Refactor/cleanup DecodeLocals, read_value_type

Changes:
Cleanup:
- Make sure read_value_type has the same interface as other
  read_* functions, i.e., returns the decoded value and writes
  the consumed length into a pointer.
- DecodeLocals is now an instance method.
- DecodeLocals should fail when given a wrong number of locals.
  Add tests to catch that.
- Fix a buggy test.

Refactoring in preparation of introducing the 'let'
instruction as per [wasm-gc]:
- DecodeLocals does not consume any input and can start from any pc.
- DecodeLocals gives the option of not appending the decoded
  locals to local_types_.
- Separate locals initialization from signature.

Bug: v8:7748
Change-Id: Iaaff87fdb9abe0ddd716484ea3fa87779d2d1a2f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2202992
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67845}

src/wasm/function-body-decoder.cc

@@ -21,10 +21,15 @@ namespace wasm {
 
 bool DecodeLocalDecls(const WasmFeatures& enabled, BodyLocalDecls* decls,
                       const byte* start, const byte* end) {
-  Decoder decoder(start, end);
-  if (WasmDecoder<Decoder::kValidate>::DecodeLocals(enabled, &decoder, nullptr,
-                                                    &decls->type_list)) {
+  WasmFeatures no_features = WasmFeatures::None();
+  WasmDecoder<Decoder::kValidate> decoder(nullptr, enabled, &no_features,
+                                          nullptr, start, end, 0);
+  decoder.local_types_ = &decls->type_list;
+  uint32_t length;
+  if (decoder.DecodeLocals(decoder.pc(), &length,
+                           decoder.DecodeLocalsMode::kUpdateLocals)) {
     DCHECK(decoder.ok());
+    decoder.consume_bytes(length);
     decls->encoded_size = decoder.pc_offset();
     return true;
   }

src/wasm/module-decoder.cc

@@ -1723,11 +1723,11 @@ class ModuleDecoderImpl : public Decoder {
   }
 
   ValueType consume_value_type() {
-    ValueType result;
-    uint32_t type_length = value_type_reader::read_value_type<kValidate>(
-        this, this->pc(), &result,
+    uint32_t type_length;
+    ValueType result = value_type_reader::read_value_type<kValidate>(
+        this, this->pc(), &type_length,
         origin_ == kWasmOrigin ? enabled_features_ : WasmFeatures::None());
-    if (type_length == 0) error(pc_, "invalid value type");
+    if (result == kWasmBottom) error(pc_, "invalid value type");
     consume_bytes(type_length);
     return result;
   }

test/cctest/wasm/test-streaming-compilation.cc

@@ -1174,9 +1174,10 @@ STREAM_TEST(TestCompileErrorFunctionName) {
       U32V_1(1),                            // functions count
       0,                                    // signature index
       kCodeSectionCode,                     // section code
-      U32V_1(3),                            // section size
+      U32V_1(4),                            // section size
       U32V_1(1),                            // functions count
-      1,                                    // body size
+      2,                                    // body size
+      0,                                    // local definitions count
       kExprNop,                             // body
   };
 
@@ -1210,7 +1211,7 @@ STREAM_TEST(TestCompileErrorFunctionName) {
     CHECK(tester.IsPromiseRejected());
     CHECK_EQ(
         "CompileError: WebAssembly.compileStreaming(): Compiling function "
-        "#0:\"f\" failed: function body must end with \"end\" opcode @+25",
+        "#0:\"f\" failed: function body must end with \"end\" opcode @+26",
         tester.error_message());
   }
 }

test/unittests/wasm/function-body-decoder-unittest.cc

@@ -3820,6 +3820,21 @@ TEST_F(LocalDeclDecoderTest, NoLocals) {
   EXPECT_TRUE(decls.type_list.empty());
 }
 
+TEST_F(LocalDeclDecoderTest, WrongLocalDeclsCount1) {
+  static const byte data[] = {1};
+  BodyLocalDecls decls(zone());
+  bool result = DecodeLocalDecls(&decls, data, data + sizeof(data));
+  EXPECT_FALSE(result);
+}
+
+TEST_F(LocalDeclDecoderTest, WrongLocalDeclsCount2) {
+  static const byte data[] = {2, 1,
+                              static_cast<byte>(kWasmI32.value_type_code())};
+  BodyLocalDecls decls(zone());
+  bool result = DecodeLocalDecls(&decls, data, data + sizeof(data));
+  EXPECT_FALSE(result);
+}
+
 TEST_F(LocalDeclDecoderTest, OneLocal) {
   WASM_FEATURE_SCOPE(anyref);
   for (size_t i = 0; i < arraysize(kValueTypes); i++) {