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

src/compiler/simd-scalar-lowering.h

Index: src/compiler/simd-scalar-lowering.h
diff --git a/src/compiler/simd-scalar-lowering.h b/src/compiler/simd-scalar-lowering.h
index 39449f4b9ff54d01a82fc25cf204bab9efa23812..4ab1ab1dec174ebd65b7520980644a7d15df03d0 100644
--- a/src/compiler/simd-scalar-lowering.h
+++ b/src/compiler/simd-scalar-lowering.h
@@ -53,6 +53,12 @@ class SimdScalarLowering {
   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;