DoNumberTagD performance improvement

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 4473 matching lines @@
 
   DoubleRegister input_reg = ToDoubleRegister(instr->value());
   Register scratch = scratch0();
   Register reg = ToRegister(instr->result());
   Register temp1 = ToRegister(instr->temp());
   Register temp2 = ToRegister(instr->temp2());
 
   DeferredNumberTagD* deferred = new(zone()) DeferredNumberTagD(this, instr);
   if (FLAG_inline_new) {
     __ LoadRoot(scratch, Heap::kHeapNumberMapRootIndex);
-    __ AllocateHeapNumber(reg, temp1, temp2, scratch, deferred->entry());
+    // We want the untagged address first for performance
+    __ AllocateHeapNumber(reg, temp1, temp2, scratch, deferred->entry(), false);
   } else {
     __ jmp(deferred->entry());
   }
   __ bind(deferred->exit());
-  __ sub(ip, reg, Operand(kHeapObjectTag));
-  __ vstr(input_reg, ip, HeapNumber::kValueOffset);
+  __ vstr(input_reg, reg, HeapNumber::kValueOffset);
+  // Now that we have finished with the object's real address tag it
+  __ add(reg, reg, Operand(kHeapObjectTag));
 }
 
 
 void LCodeGen::DoDeferredNumberTagD(LNumberTagD* instr) {
   // TODO(3095996): Get rid of this. For now, we need to make the
   // result register contain a valid pointer because it is already
   // contained in the register pointer map.
   Register reg = ToRegister(instr->result());
   __ mov(reg, Operand(0));
 
   PushSafepointRegistersScope scope(this, Safepoint::kWithRegisters);
   CallRuntimeFromDeferred(Runtime::kAllocateHeapNumber, 0, instr);
+  __ sub(r0, r0, Operand(kHeapObjectTag));
   __ StoreToSafepointRegisterSlot(r0, reg);
 }
 
 
 void LCodeGen::DoSmiTag(LSmiTag* instr) {
   ASSERT(!instr->hydrogen_value()->CheckFlag(HValue::kCanOverflow));
   __ SmiTag(ToRegister(instr->result()), ToRegister(instr->value()));
 }
 
 
@@ skipping 1152 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal