[a64] Omit redundant smi checks in write barriers.

src/a64/lithium-codegen-a64.cc

Index: src/a64/lithium-codegen-a64.cc
diff --git a/src/a64/lithium-codegen-a64.cc b/src/a64/lithium-codegen-a64.cc
index da03ccc214700a949048b590d342a434f84521c2..875b4505cb33f800d66b7d0510315b450afe6c25 100644
--- a/src/a64/lithium-codegen-a64.cc
+++ b/src/a64/lithium-codegen-a64.cc
@@ -5051,11 +5051,17 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
   }
 
   Handle<Map> transition = instr->transition();
+  SmiCheck check_needed =
+      instr->hydrogen()->value()->IsHeapObject()
+          ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
 
   if (FLAG_track_heap_object_fields && representation.IsHeapObject()) {
     Register value = ToRegister(instr->value());
     if (!instr->hydrogen()->value()->type().IsHeapObject()) {
       DeoptimizeIfSmi(value, instr->environment());
+
+      // We know that value is a smi now, so we can omit the check below.
+      check_needed = OMIT_SMI_CHECK;
     }
   } else if (representation.IsDouble()) {
     ASSERT(transition.is_null());
@@ -5087,9 +5093,6 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
   // Do the store.
   Register value = ToRegister(instr->value());
   Register destination;
-  SmiCheck check_needed =
-      instr->hydrogen()->value()->IsHeapObject()
-          ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
   if (access.IsInobject()) {
     destination = object;
   } else {