Omit redundant smi checks in write barriers.

src/x64/lithium-codegen-x64.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 3848 matching lines @@
       __ store_rax(ToExternalReference(object));
     } else {
       Register object = ToRegister(instr->object());
       __ Store(MemOperand(object, offset), value, representation);
     }
     return;
   }
 
   Register object = ToRegister(instr->object());
   Handle<Map> transition = instr->transition();
+  SmiCheck check_needed = hinstr->value()->IsHeapObject()
+                          ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
 
   if (FLAG_track_fields && representation.IsSmi()) {
     if (instr->value()->IsConstantOperand()) {
       LConstantOperand* operand_value = LConstantOperand::cast(instr->value());
       if (!IsInteger32Constant(operand_value) &&
           !IsSmiConstant(operand_value)) {
         DeoptimizeIf(no_condition, instr->environment());
       }
     }
   } else if (FLAG_track_heap_object_fields && representation.IsHeapObject()) {
     if (instr->value()->IsConstantOperand()) {
       LConstantOperand* operand_value = LConstantOperand::cast(instr->value());
       if (IsInteger32Constant(operand_value)) {
         DeoptimizeIf(no_condition, instr->environment());
       }
     } else {
       if (!hinstr->value()->type().IsHeapObject()) {
         Register value = ToRegister(instr->value());
         Condition cc = masm()->CheckSmi(value);
         DeoptimizeIf(cc, 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(!hinstr->NeedsWriteBarrier());
     XMMRegister value = ToDoubleRegister(instr->value());
     __ movsd(FieldOperand(object, offset), value);
     return;
   }
@@ skipping 10 matching lines @@
                           HeapObject::kMapOffset,
                           kScratchRegister,
                           temp,
                           kSaveFPRegs,
                           OMIT_REMEMBERED_SET,
                           OMIT_SMI_CHECK);
     }
   }
 
   // Do the store.
-  SmiCheck check_needed = hinstr->value()->IsHeapObject()
-                          ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
-
   Register write_register = object;
   if (!access.IsInobject()) {
     write_register = ToRegister(instr->temp());
     __ movp(write_register, FieldOperand(object, JSObject::kPropertiesOffset));
   }
 
   if (representation.IsSmi() &&
       hinstr->value()->representation().IsInteger32()) {
     ASSERT(hinstr->store_mode() == STORE_TO_INITIALIZED_ENTRY);
 #ifdef DEBUG
@@ skipping 1616 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64