From 5f29f9bd8ee446a921db3728c11e6216197d04e3 Mon Sep 17 00:00:00 2001
From: "fschneider@chromium.org"
 <fschneider@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Thu, 12 May 2011 14:56:56 +0000
Subject: [PATCH] Don't use environment values at certain
 deoptimize-instructions.

If a HDeoptimize does not cut away parts of the control-flow-graph
we don't need to insert uses to correctly elimiate dead phis since
the full function is visible to the optimizing compiler.

This is a small improvement of the change r7221 which fixed a problem
when deoptimizing on never executed case-clauses.
Review URL: http://codereview.chromium.org/7012010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7877 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/hydrogen-instructions.h |  5 +++++
 src/hydrogen.cc             | 15 +++++++++------
 src/hydrogen.h              |  6 +++---
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index cca4150e1..03ff00751 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -862,6 +862,11 @@ class HDeoptimize: public HControlInstruction {
 
   DECLARE_CONCRETE_INSTRUCTION(Deoptimize)
 
+  enum UseEnvironment {
+    kNoUses,
+    kUseAll
+  };
+
  protected:
   virtual void InternalSetOperandAt(int index, HValue* value) {
     values_[index] = value;
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 614113aac..97d7c8394 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -115,12 +115,13 @@ void HBasicBlock::AddInstruction(HInstruction* instr) {
 }
 
 
-HDeoptimize* HBasicBlock::CreateDeoptimize() {
+HDeoptimize* HBasicBlock::CreateDeoptimize(
+    HDeoptimize::UseEnvironment has_uses) {
   ASSERT(HasEnvironment());
-  HEnvironment* environment = last_environment();
+  if (has_uses == HDeoptimize::kNoUses) return new(zone()) HDeoptimize(0);
 
+  HEnvironment* environment = last_environment();
   HDeoptimize* instr = new(zone()) HDeoptimize(environment->length());
-
   for (int i = 0; i < environment->length(); i++) {
     HValue* val = environment->values()->at(i);
     instr->AddEnvironmentValue(val);
@@ -2490,7 +2491,9 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
     // Unconditionally deoptimize on the first non-smi compare.
     clause->RecordTypeFeedback(oracle());
     if (!clause->IsSmiCompare()) {
-      current_block()->FinishExitWithDeoptimization();
+      // Finish with deoptimize and add uses of enviroment values to
+      // account for invisible uses.
+      current_block()->FinishExitWithDeoptimization(HDeoptimize::kUseAll);
       set_current_block(NULL);
       break;
     }
@@ -3237,7 +3240,7 @@ void HGraphBuilder::HandlePolymorphicStoreNamedField(Assignment* expr,
   // know about and do not want to handle ones we've never seen.  Otherwise
   // use a generic IC.
   if (count == types->length() && FLAG_deoptimize_uncommon_cases) {
-    current_block()->FinishExitWithDeoptimization();
+    current_block()->FinishExitWithDeoptimization(HDeoptimize::kNoUses);
   } else {
     HInstruction* instr = BuildStoreNamedGeneric(object, name, value);
     instr->set_position(expr->position());
@@ -3916,7 +3919,7 @@ void HGraphBuilder::HandlePolymorphicCallNamed(Call* expr,
   // know about and do not want to handle ones we've never seen.  Otherwise
   // use a generic IC.
   if (count == types->length() && FLAG_deoptimize_uncommon_cases) {
-    current_block()->FinishExitWithDeoptimization();
+    current_block()->FinishExitWithDeoptimization(HDeoptimize::kNoUses);
   } else {
     HValue* context = environment()->LookupContext();
     HCallNamed* call = new(zone()) HCallNamed(context, name, argument_count);
diff --git a/src/hydrogen.h b/src/hydrogen.h
index 326f82a65..fb9b117a6 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -125,8 +125,8 @@ class HBasicBlock: public ZoneObject {
   void AddSimulate(int id) { AddInstruction(CreateSimulate(id)); }
   void AssignCommonDominator(HBasicBlock* other);
 
-  void FinishExitWithDeoptimization() {
-    FinishExit(CreateDeoptimize());
+  void FinishExitWithDeoptimization(HDeoptimize::UseEnvironment has_uses) {
+    FinishExit(CreateDeoptimize(has_uses));
   }
 
   // Add the inlined function exit sequence, adding an HLeaveInlined
@@ -153,7 +153,7 @@ class HBasicBlock: public ZoneObject {
   void AddDominatedBlock(HBasicBlock* block);
 
   HSimulate* CreateSimulate(int id);
-  HDeoptimize* CreateDeoptimize();
+  HDeoptimize* CreateDeoptimize(HDeoptimize::UseEnvironment has_uses);
 
   int block_id_;
   HGraph* graph_;
-- 
2.34.1