X64: Make comparisons work on zero-extended smis.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
===================================================================
--- src/x64/assembler-x64.cc	(revision 2363)
+++ src/x64/assembler-x64.cc	(working copy)
@@ -1449,7 +1449,7 @@
   last_pc_ = pc_;
   if (reg.is(rax)) {
     emit(0xA8);
-    emit(mask);
+    emit(mask.value_);  // Low byte emitted.
   } else {
     if (reg.code() > 3) {
       // Register is not one of al, bl, cl, dl.  Its encoding needs REX.
@@ -1473,6 +1473,15 @@
 }
 
 
+void Assembler::testl(Register dst, Register src) {
+  EnsureSpace ensure_space(this);
+  last_pc_ = pc_;
+  emit_optional_rex_32(dst, src);
+  emit(0x85);
+  emit_modrm(dst, src);
+}
+
+
 void Assembler::testl(Register reg, Immediate mask) {
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;