DoNumberTagD performance improvement

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index b5a0f9af31919d948e1ec2fa0fc6f77e47c5013f..52864d3c2b58625ff89bfe3ccb0fbefe92b6f831 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -4491,13 +4491,15 @@ void LCodeGen::DoNumberTagD(LNumberTagD* instr) {
   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));
 }
 
 
@@ -4510,6 +4512,7 @@ void LCodeGen::DoDeferredNumberTagD(LNumberTagD* instr) {
 
   PushSafepointRegistersScope scope(this, Safepoint::kWithRegisters);
   CallRuntimeFromDeferred(Runtime::kAllocateHeapNumber, 0, instr);
+  __ sub(r0, r0, Operand(kHeapObjectTag));
   __ StoreToSafepointRegisterSlot(r0, reg);
 }