[WASM] Simplify SIMD shuffle opcodes.

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

 // Copyright 2017 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_FUNCTION_BODY_DECODER_IMPL_H_
 #define V8_WASM_FUNCTION_BODY_DECODER_IMPL_H_
 
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-opcodes.h"
 
@@ skipping 295 matching lines @@
 template <bool checked>
 struct SimdShiftOperand {
   uint8_t shift;
   unsigned length = 1;
 
   inline SimdShiftOperand(Decoder* decoder, const byte* pc) {
     shift = decoder->read_u8<checked>(pc + 2, "shift");
   }
 };
 
-// Operand for SIMD shuffle operations.
+// Operand for SIMD S8x16 shuffle operations.
 template <bool checked>
-struct SimdShuffleOperand {
-  uint8_t shuffle[16];
-  unsigned lanes;
+struct Simd8x16ShuffleOperand {
+  uint8_t shuffle[kSimd128Size];
 
-  inline SimdShuffleOperand(Decoder* decoder, const byte* pc, unsigned lanes_) {
-    lanes = lanes_;
-    for (unsigned i = 0; i < lanes; i++) {
+  inline Simd8x16ShuffleOperand(Decoder* decoder, const byte* pc) {
+    for (uint32_t i = 0; i < kSimd128Size; ++i) {
       shuffle[i] = decoder->read_u8<checked>(pc + 2 + i, "shuffle");
     }
   }
 };
 
 #undef CHECKED_COND
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_FUNCTION_BODY_DECODER_IMPL_H_