Omit redundant smi checks in write barriers.

src/arm/lithium-codegen-arm.cc

 // Copyright 2012 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 4033 matching lines @@
   int offset = access.offset();
 
   if (access.IsExternalMemory()) {
     Register value = ToRegister(instr->value());
     MemOperand operand = MemOperand(object, offset);
     __ Store(value, operand, 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()) {
       __ SmiTst(value);
       DeoptimizeIf(eq, 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());
     DwVfpRegister value = ToDoubleRegister(instr->value());
     __ vstr(value, FieldMemOperand(object, offset));
     return;
   }
 
   if (!transition.is_null()) {
     __ mov(scratch, Operand(transition));
     __ str(scratch, FieldMemOperand(object, HeapObject::kMapOffset));
     if (instr->hydrogen()->NeedsWriteBarrierForMap()) {
       Register temp = ToRegister(instr->temp());
       // Update the write barrier for the map field.
       __ RecordWriteField(object,
                           HeapObject::kMapOffset,
                           scratch,
                           temp,
                           GetLinkRegisterState(),
                           kSaveFPRegs,
                           OMIT_REMEMBERED_SET,
                           OMIT_SMI_CHECK);
     }
   }
 
   // Do the store.
   Register value = ToRegister(instr->value());
-  SmiCheck check_needed =
-      instr->hydrogen()->value()->IsHeapObject()
-          ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
   if (access.IsInobject()) {
     MemOperand operand = FieldMemOperand(object, offset);
     __ Store(value, operand, representation);
     if (instr->hydrogen()->NeedsWriteBarrier()) {
       // Update the write barrier for the object for in-object properties.
       __ RecordWriteField(object,
                           offset,
                           value,
                           scratch,
                           GetLinkRegisterState(),
@@ skipping 1637 matching lines @@
   __ sub(scratch, result, Operand::PointerOffsetFromSmiKey(index));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal