[wasm] Fix OpcodeLength() calculation.

src/wasm/ast-decoder.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_AST_DECODER_H_
 #define V8_WASM_AST_DECODER_H_
 
 #include "src/signature.h"
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-opcodes.h"
@@ skipping 28 matching lines @@
   inline ImmI8Operand(Decoder* decoder, const byte* pc) {
     value = bit_cast<int8_t>(decoder->checked_read_u8(pc, 1, "immi8"));
     length = 1;
   }
 };
 
 struct ImmI32Operand {
   int32_t value;
   int length;
   inline ImmI32Operand(Decoder* decoder, const byte* pc) {
-    value =
-        bit_cast<int32_t>(decoder->checked_read_i32v(pc, 1, &length, "immi32"));
+    value = decoder->checked_read_i32v(pc, 1, &length, "immi32");
   }
 };
 
 struct ImmI64Operand {
   int64_t value;
   int length;
   inline ImmI64Operand(Decoder* decoder, const byte* pc) {
-    value =
-        bit_cast<int64_t>(decoder->checked_read_i64v(pc, 1, &length, "immi64"));
+    value = decoder->checked_read_i64v(pc, 1, &length, "immi64");
   }
 };
 
 struct ImmF32Operand {
   float value;
   int length;
   inline ImmF32Operand(Decoder* decoder, const byte* pc) {
     value = bit_cast<float>(decoder->checked_read_u32(pc, 1, "immf32"));
     length = 4;
   }
@@ skipping 157 matching lines @@
 int OpcodeLength(const byte* pc, const byte* end);
 
 // Computes the arity (number of sub-nodes) of the opcode at the given address.
 int OpcodeArity(ModuleEnv* module, FunctionSig* sig, const byte* pc,
                 const byte* end);
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_AST_DECODER_H_