[WASM SIMD] Implement primitive shuffles.

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 304 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 concatenation operations.
+template <bool checked>
+struct SimdConcatOperand {
+  uint8_t bytes;
+  unsigned length;
+
+  inline SimdConcatOperand(Decoder* decoder, const byte* pc) {
+    bytes = decoder->read_u8<checked>(pc + 2, "bytes");
+    length = 1;
+  }
+};
+
 #undef CHECKED_COND
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_FUNCTION_BODY_DECODER_IMPL_H_