HSubAllocatedObject instruction allows hydrogen code to carve up

src/ia32/lithium-ia32.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 274 matching lines @@
 
 void LTypeofIsAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if typeof ");
   value()->PrintTo(stream);
   stream->Add(" == \"%s\" then B%d else B%d",
               *hydrogen()->type_literal()->ToCString(),
               true_block_id(), false_block_id());
 }
 
 
+void LSubAllocatedObject::PrintDataTo(StringStream* stream) {
+  stream->Add(" = ");
+  base_object()->PrintTo(stream);
+  stream->Add("+%d", offset());

[Hannes Payer (out of office), 2013/03/13 08:48:39]

do you need a blank before +?

[mvstanton, 2013/03/13 10:14:40]

I'll do a blank before and after the plus, that way it'll be like
"sub-allocated-object @ecx = @eax + 16"

+}
+
+
 void LCallConstantFunction::PrintDataTo(StringStream* stream) {
   stream->Add("#%d / ", arity());
 }
 
 
 void LUnaryMathOperation::PrintDataTo(StringStream* stream) {
   stream->Add("/%s ", hydrogen()->OpName());
   value()->PrintTo(stream);
 }
 
@@ skipping 769 matching lines @@
 }
 
 
 LInstruction* LChunkBuilder::DoPushArgument(HPushArgument* instr) {
   ++argument_count_;
   LOperand* argument = UseAny(instr->argument());
   return new(zone()) LPushArgument(argument);
 }
 
 
+LInstruction* LChunkBuilder::DoSubAllocatedObject(
+    HSubAllocatedObject* sub_object) {
+  bool zero_offset = sub_object->offset() == 0;

[Hannes Payer (out of office), 2013/03/13 08:48:39]

remove this and just just do return sub_object->offset() == 0 ?
DefineSameAsFirst(result) : DefineAsRegister(result);

[Michael Starzinger, 2013/03/13 09:12:35]

Does this actually happen in practice? If not I would just remove this
optimization for now. The instruction should be removed completely from the
graph during the canonicalization phase for zero offsets if we ever need this.

[mvstanton, 2013/03/13 10:14:40]

good point, thanks. done.

[mvstanton, 2013/03/13 10:14:40]

I got rid of zero_offset, per Michael's advice.

+  LOperand* base_object = UseRegister(sub_object->base_object());

[Michael Starzinger, 2013/03/13 09:12:35]

The base register and the result register can be the same, better use
"UseRegisterAtStart" for the base register.

[mvstanton, 2013/03/13 10:14:40]

Done.

+  LSubAllocatedObject* result =
+      new(zone()) LSubAllocatedObject(base_object);
+  return zero_offset ? DefineSameAsFirst(result) : DefineAsRegister(result);
+}
+
+
 LInstruction* LChunkBuilder::DoThisFunction(HThisFunction* instr) {
   return instr->HasNoUses()
       ? NULL
       : DefineAsRegister(new(zone()) LThisFunction);
 }
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
   if (instr->HasNoUses()) return NULL;
 
@@ skipping 1502 matching lines @@
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseTempRegister(instr->index());
   return DefineSameAsFirst(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32