[V8] Implement SIMD Boolean vector types to allow mask registers.

src/compiler/arm/code-generator-arm.cc

Index: src/compiler/arm/code-generator-arm.cc
diff --git a/src/compiler/arm/code-generator-arm.cc b/src/compiler/arm/code-generator-arm.cc
index ca0174569dd662bd3af7853357b2401b5e8f593f..a0e85d63d54ce4733d380c5ada92a23857cd84b4 100644
--- a/src/compiler/arm/code-generator-arm.cc
+++ b/src/compiler/arm/code-generator-arm.cc
@@ -1927,25 +1927,22 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       break;
     }
     case kArmSimd32x4Select: {
-      // Canonicalize input 0 lanes to all 0's or all 1's and move to dest.
-      __ vtst(Neon32, i.OutputSimd128Register(), i.InputSimd128Register(0),
-              i.InputSimd128Register(0));
+      // vbsl is a ternary opcode, so move input 0 into dest.
+      __ Move(i.OutputSimd128Register(), i.InputSimd128Register(0));

[gdeepti, 2017/02/17 17:51:48]

Would it be possible to use DefineSameAsFirst in the instruction selector with a
different Visit method to  remove the Move instruction here? Same comment for
the two Select opcodes below. 

[bbudge, 2017/02/17 23:39:56]

Yes, that seems better. Also, I noticed that these ops are now identical for all
SIMD formats, so I merged them into a single case.

       __ vbsl(i.OutputSimd128Register(), i.InputSimd128Register(1),
               i.InputSimd128Register(2));
       break;
     }
     case kArmSimd16x8Select: {
-      // Canonicalize input 0 lanes to all 0's or all 1's and move to dest.
-      __ vtst(Neon16, i.OutputSimd128Register(), i.InputSimd128Register(0),
-              i.InputSimd128Register(0));
+      // vbsl is a ternary opcode, so move input 0 into dest.
+      __ Move(i.OutputSimd128Register(), i.InputSimd128Register(0));
       __ vbsl(i.OutputSimd128Register(), i.InputSimd128Register(1),
               i.InputSimd128Register(2));
       break;
     }
     case kArmSimd8x16Select: {
-      // Canonicalize input 0 lanes to all 0's or all 1's and move to dest.
-      __ vtst(Neon8, i.OutputSimd128Register(), i.InputSimd128Register(0),
-              i.InputSimd128Register(0));
+      // vbsl is a ternary opcode, so move input 0 into dest.
+      __ Move(i.OutputSimd128Register(), i.InputSimd128Register(0));
       __ vbsl(i.OutputSimd128Register(), i.InputSimd128Register(1),
               i.InputSimd128Register(2));
       break;