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 4428 matching lines @@
     }
     __ vmov(flt_scratch, src);
     __ vcvt_f64_s32(dbl_scratch, flt_scratch);
   } else {
     __ vmov(flt_scratch, src);
     __ vcvt_f64_u32(dbl_scratch, flt_scratch);
   }
 
   if (FLAG_inline_new) {
     __ LoadRoot(r6, Heap::kHeapNumberMapRootIndex);
-    __ AllocateHeapNumber(r5, r3, r4, r6, &slow);
+    __ AllocateHeapNumber(r5, r3, r4, r6, &slow, DONT_TAG_RESULT);
     __ Move(dst, r5);
     __ b(&done);
   }
 
   // Slow case: Call the runtime system to do the number allocation.
   __ bind(&slow);
 
   // TODO(3095996): Put a valid pointer value in the stack slot where the result
   // register is stored, as this register is in the pointer map, but contains an
   // integer value.
   __ mov(ip, Operand(0));
   __ StoreToSafepointRegisterSlot(ip, dst);
   CallRuntimeFromDeferred(Runtime::kAllocateHeapNumber, 0, instr);
   __ Move(dst, r0);
+  __ sub(dst, dst, Operand(kHeapObjectTag));
 
   // Done. Put the value in dbl_scratch into the value of the allocated heap
   // number.
   __ bind(&done);
-  __ sub(ip, dst, Operand(kHeapObjectTag));
-  __ vstr(dbl_scratch, ip, HeapNumber::kValueOffset);
+  __ vstr(dbl_scratch, dst, HeapNumber::kValueOffset);
+  __ add(dst, dst, Operand(kHeapObjectTag));
   __ StoreToSafepointRegisterSlot(dst, dst);
 }
 
 
 void LCodeGen::DoNumberTagD(LNumberTagD* instr) {
   class DeferredNumberTagD: public LDeferredCode {
    public:
     DeferredNumberTagD(LCodeGen* codegen, LNumberTagD* instr)
         : LDeferredCode(codegen), instr_(instr) { }
     virtual void Generate() { codegen()->DoDeferredNumberTagD(instr_); }
     virtual LInstruction* instr() { return instr_; }
    private:
     LNumberTagD* instr_;
   };
 
   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(),
+                          DONT_TAG_RESULT);
   } 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 154 matching lines @@
     DeferredTaggedToI(LCodeGen* codegen, LTaggedToI* instr)
         : LDeferredCode(codegen), instr_(instr) { }
     virtual void Generate() { codegen()->DoDeferredTaggedToI(instr_); }
     virtual LInstruction* instr() { return instr_; }
    private:
     LTaggedToI* instr_;
   };
 
   LOperand* input = instr->value();
   ASSERT(input->IsRegister());
-  ASSERT(input->Equals(instr->result()));
+  ASSERT(input->Equals(instrt->result()));

[danno, 2012/10/11 13:03:57]

I think the above change is a typo.

[aberent, 2012/10/11 15:16:53]

Done.

 
   Register input_reg = ToRegister(input);
 
   DeferredTaggedToI* deferred = new(zone()) DeferredTaggedToI(this, instr);
 
   // Optimistically untag the input.
   // If the input is a HeapObject, SmiUntag will set the carry flag.
   __ SmiUntag(input_reg, SetCC);
   // Branch to deferred code if the input was tagged.
   // The deferred code will take care of restoring the tag.
@@ skipping 977 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal