[date] Refactor the %_DateField intrinsic to be optimizable.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 30c35b1f0f93030caa07b4a8f69ddbfe1615fc55..ee0ec27fcf21100efd40b84928ff3eb8e9f2171a 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -1790,18 +1790,13 @@ void LCodeGen::DoDateField(LDateField* instr) {
   Register result = ToRegister(instr->result());
   Register scratch = ToRegister(instr->temp());
   Smi* index = instr->index();
-  Label runtime, done;
   DCHECK(object.is(result));
   DCHECK(object.is(eax));
 
-  __ test(object, Immediate(kSmiTagMask));
-  DeoptimizeIf(zero, instr, Deoptimizer::kSmi);
-  __ CmpObjectType(object, JS_DATE_TYPE, scratch);
-  DeoptimizeIf(not_equal, instr, Deoptimizer::kNotADateObject);
-
   if (index->value() == 0) {
     __ mov(result, FieldOperand(object, JSDate::kValueOffset));
   } else {
+    Label runtime, done;
     if (index->value() < JSDate::kFirstUncachedField) {
       ExternalReference stamp = ExternalReference::date_cache_stamp(isolate());
       __ mov(scratch, Operand::StaticVariable(stamp));