[turbofan][X64] Movzxbl/Movsxbl/Movzxwl/Movsxwl also zero extend to 64bit.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index 7c72587ab69e1ad7e20707ae57bc070e9326ed2e..646d914b2eae7954483782d8444445edc712f690 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -1250,6 +1250,22 @@ bool ZeroExtendsWord32ToWord64(Node* node) {
           return false;
       }
     }
+    case IrOpcode::kLoad: {
+      // The movzxbl/movsxbl/movzxwl/movsxwl operations implicitly zero-extend
+      // to 64-bit on x64,
+      // so the zero-extension is a no-op.
+      LoadRepresentation load_rep = LoadRepresentationOf(node->op());
+      ArchOpcode opcode = GetLoadOpcode(load_rep);

[Benedikt Meurer, 2016/10/17 08:20:42]

How about pattern matching the representation instead of the x64 opcode?

+      switch (opcode) {
+        case kX64Movzxbl:
+        case kX64Movsxbl:
+        case kX64Movzxwl:
+        case kX64Movsxwl:
+          return true;
+        default:
+          return false;
+      }
+    }
     default:
       return false;
   }
@@ -1265,6 +1281,7 @@ void InstructionSelector::VisitChangeUint32ToUint64(Node* node) {
     // zero-extension is a no-op.
     return EmitIdentity(node);
   }
+

[titzer, 2016/10/17 08:13:35]

Spurious whitespace change.

   Emit(kX64Movl, g.DefineAsRegister(node), g.Use(value));
 }