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

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 3c845cba296438883f75633af7084410e9528df4..8a15bd59e62108ebea0779614582ceac5fbf4e57 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1930,20 +1930,15 @@ 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(r0));
   DCHECK(!scratch.is(scratch0()));
   DCHECK(!scratch.is(object));
 
-  __ SmiTst(object);
-  DeoptimizeIf(eq, instr, Deoptimizer::kSmi);
-  __ CompareObjectType(object, scratch, scratch, JS_DATE_TYPE);
-  DeoptimizeIf(ne, instr, Deoptimizer::kNotADateObject);
-
   if (index->value() == 0) {
     __ ldr(result, FieldMemOperand(object, JSDate::kValueOffset));
   } else {
+    Label runtime, done;
     if (index->value() < JSDate::kFirstUncachedField) {
       ExternalReference stamp = ExternalReference::date_cache_stamp(isolate());
       __ mov(scratch, Operand(stamp));