Ensure using byte registers for byte instructions on ia32 and x64.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index ff8aeefe2c73d4ed19bb5cc1417232ee3c14db2a..4129db69db5c5e405b3fee5741b7c9d207bd4657 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1793,11 +1793,10 @@ void LCodeGen::EmitClassOfTest(Label* is_true,
     // Faster code path to avoid two compares: subtract lower bound from the
     // actual type and do a signed compare with the width of the type range.
     __ movq(temp, FieldOperand(input, HeapObject::kMapOffset));
-    __ movq(temp2, FieldOperand(temp, Map::kInstanceTypeOffset));
-    __ subb(temp2, Immediate(FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
-    __ cmpb(temp2,
-            Immediate(static_cast<int8_t>(LAST_NONCALLABLE_SPEC_OBJECT_TYPE -
-                                          FIRST_NONCALLABLE_SPEC_OBJECT_TYPE)));
+    __ movzxbl(temp2, FieldOperand(temp, Map::kInstanceTypeOffset));
+    __ subq(temp2, Immediate(FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
+    __ cmpq(temp2, Immediate(LAST_NONCALLABLE_SPEC_OBJECT_TYPE -
+                             FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
     __ j(above, is_false);
   }