Revert of Remove SIMD.js from V8.

src/full-codegen/x64/full-codegen-x64.cc

 // Copyright 2012 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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/builtins/builtins-constructor.h"
 #include "src/code-factory.h"
@@ skipping 2508 matching lines @@
     __ JumpIfSmi(rax, if_false);
     __ CompareRoot(rax, Heap::kNullValueRootIndex);
     __ j(equal, if_true);
     STATIC_ASSERT(LAST_JS_RECEIVER_TYPE == LAST_TYPE);
     __ CmpObjectType(rax, FIRST_JS_RECEIVER_TYPE, rdx);
     __ j(below, if_false);
     // Check for callable or undetectable objects => false.
     __ testb(FieldOperand(rdx, Map::kBitFieldOffset),
              Immediate((1 << Map::kIsCallable) | (1 << Map::kIsUndetectable)));
     Split(zero, if_true, if_false, fall_through);
+// clang-format off
+#define SIMD128_TYPE(TYPE, Type, type, lane_count, lane_type)   \
+  } else if (String::Equals(check, factory->type##_string())) { \
+    __ JumpIfSmi(rax, if_false);                                \
+    __ movp(rax, FieldOperand(rax, HeapObject::kMapOffset));    \
+    __ CompareRoot(rax, Heap::k##Type##MapRootIndex);           \
+    Split(equal, if_true, if_false, fall_through);
+  SIMD128_TYPES(SIMD128_TYPE)
+#undef SIMD128_TYPE
+    // clang-format on
   } else {
     if (if_false != fall_through) __ jmp(if_false);
   }
   context()->Plug(if_true, if_false);
 }
 
 
 void FullCodeGenerator::VisitCompareOperation(CompareOperation* expr) {
   Comment cmnt(masm_, "[ CompareOperation");
 
@@ skipping 211 matching lines @@
   DCHECK_EQ(
       isolate->builtins()->OnStackReplacement()->entry(),
       Assembler::target_address_at(call_target_address, unoptimized_code));
   return ON_STACK_REPLACEMENT;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64