[simd] Disable Simd Scalar lowering for x64, enable tests for all other architectures.

src/compiler/simd-scalar-lowering.h

 // Copyright 2016 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_COMPILER_SIMD_SCALAR_LOWERING_H_
 #define V8_COMPILER_SIMD_SCALAR_LOWERING_H_
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/machine-operator.h"
@@ skipping 35 matching lines @@
   void LowerNode(Node* node);
   bool DefaultLowering(Node* node);
 
   void ReplaceNode(Node* old, Node** new_nodes);
   bool HasReplacement(size_t index, Node* node);
   Node** GetReplacements(Node* node);
   Node** GetReplacementsWithType(Node* node, SimdType type);
   SimdType ReplacementType(Node* node);
   void PreparePhiReplacement(Node* phi);
   void SetLoweredType(Node* node, Node* output);
+  bool IsScalarLoweringEnabled() {

[bbudge, 2016/11/18 19:30:59]

How hard is it to just not even create a SimdScalarLowering phase on platforms
that support SIMD natively? I think that would be cleaner than creating this
object and then silently doing nothing when the lower function is called.

Also, can you use the Assembler::SupportsSimd128 function to determine whether
lowering is necessary?

https://cs.chromium.org/chromium/src/v8/src/x64/assembler-x64-inl.h?rcl=14792...

[gdeepti, 2016/11/21 19:30:02]

Fixed to use SupportsSimd128 function, moved conditional to wasm-compiler.cc so
object is not created.  

+#if V8_TARGET_ARCH_X64
+    return false;
+#endif
+    return true;
+  }
 
   struct NodeState {
     Node* node;
     int input_index;
   };
 
   Zone* zone_;
   Graph* const graph_;
   MachineOperatorBuilder* machine_;
   CommonOperatorBuilder* common_;
   NodeMarker<State> state_;
   ZoneDeque<NodeState> stack_;
   Replacement* replacements_;
   Signature<MachineRepresentation>* signature_;
   Node* placeholder_;
   int parameter_count_after_lowering_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMD_SCALAR_LOWERING_H_