Add support to load/store byte fields.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 189e9e89b6a07243c07b65dcd26fbcf464136ca1..959e4a46e87b1ddcd719a50a103c60e09eafbf68 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -947,6 +947,28 @@ void MacroAssembler::Cvtlsi2sd(XMMRegister dst, const Operand& src) {
 }
 
 
+void MacroAssembler::Load(Register dst, const Operand& src, Representation r) {
+  if (r.IsByte()) {
+    movzxbl(dst, src);
+  } else if (r.IsInteger32()) {
+    movl(dst, src);
+  } else {
+    movq(dst, src);
+  }
+}
+
+
+void MacroAssembler::Store(const Operand& dst, Register src, Representation r) {
+  if (r.IsByte()) {
+    movb(dst, src);
+  } else if (r.IsInteger32()) {
+    movl(dst, src);
+  } else {
+    movq(dst, src);
+  }
+}
+
+
 void MacroAssembler::Set(Register dst, int64_t x) {
   if (x == 0) {
     xorl(dst, dst);