[a64] Omit redundant smi checks in write barriers.

src/a64/lithium-codegen-a64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5033 matching lines @@
   HObjectAccess access = instr->hydrogen()->access();
   int offset = access.offset();
 
   if (access.IsExternalMemory()) {
     Register value = ToRegister(instr->value());
     __ Store(value, MemOperand(object, offset), representation);
     return;
   }
 
   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());
     ASSERT(access.IsInobject());
     ASSERT(!instr->hydrogen()->NeedsWriteBarrier());
     FPRegister value = ToDoubleRegister(instr->value());
     __ Str(value, FieldMemOperand(object, offset));
     return;
   }
 
@@ skipping 11 matching lines @@
                           GetLinkRegisterState(),
                           kSaveFPRegs,
                           OMIT_REMEMBERED_SET,
                           OMIT_SMI_CHECK);
     }
   }
 
   // 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 {
     __ Ldr(temp0, FieldMemOperand(object, JSObject::kPropertiesOffset));
     destination = temp0;
   }
 
   if (representation.IsSmi() &&
       instr->hydrogen()->value()->representation().IsInteger32()) {
     ASSERT(instr->hydrogen()->store_mode() == STORE_TO_INITIALIZED_ENTRY);
@@ skipping 591 matching lines @@
   __ Bind(&out_of_object);
   __ Ldr(result, FieldMemOperand(object, JSObject::kPropertiesOffset));
   // Index is equal to negated out of object property index plus 1.
   __ Sub(result, result, Operand::UntagSmiAndScale(index, kPointerSizeLog2));
   __ Ldr(result, FieldMemOperand(result,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ Bind(&done);
 }
 
 } }  // namespace v8::internal