Fix bug with GVN on array loads.

This fixes a bug where an array load was incorrectly hoisted by GVN.

BUG=85177
TEST=mjsunit/regress/regress-85177.js
Review URL: http://codereview.chromium.org/7003054

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8230 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -1734,7 +1734,6 @@ void HSimulate::Verify() {
 
 void HBoundsCheck::Verify() {
   HInstruction::Verify();
-  ASSERT(HasNoUses());
 }
 
 

src/hydrogen-instructions.h

@@ -595,6 +595,7 @@ class HValue: public ZoneObject {
   void SetOperandAt(int index, HValue* value);
 
   void DeleteAndReplaceWith(HValue* other);
+  void ReplaceAllUsesWith(HValue* other);
   bool HasNoUses() const { return use_list_ == NULL; }
   bool HasMultipleUses() const {
     return use_list_ != NULL && use_list_->tail() != NULL;
@@ -684,8 +685,6 @@ class HValue: public ZoneObject {
   // removed list node or NULL.
   HUseListNode* RemoveUse(HValue* value, int index);
 
-  void ReplaceAllUsesWith(HValue* other);
-
   void RegisterUse(int index, HValue* new_value);
 
   HBasicBlock* block_;
@@ -2403,6 +2402,7 @@ class HBoundsCheck: public HBinaryOperation {
  public:
   HBoundsCheck(HValue* index, HValue* length)
       : HBinaryOperation(index, length) {
+    set_representation(Representation::Integer32());
     SetFlag(kUseGVN);
   }
 

src/hydrogen.cc

@@ -2262,10 +2262,32 @@ HGraph* HGraphBuilder::CreateGraph() {
     gvn.Analyze();
   }
 
+  // Replace the results of check instructions with the original value, if the
+  // result is used. This is safe now, since we don't do code motion after this
+  // point. It enables better register allocation since the value produced by
+  // check instructions is really a copy of the original value.
+  graph()->ReplaceCheckedValues();
+
   return graph();
 }
 
 
+void HGraph::ReplaceCheckedValues() {
+  HPhase phase("Replace checked values", this);
+  for (int i = 0; i < blocks()->length(); ++i) {
+    HInstruction* instr = blocks()->at(i)->first();
+    while (instr != NULL) {
+      if (instr->IsBoundsCheck()) {
+        // Replace all uses of the checked value with the original input.
+        ASSERT(instr->UseCount() > 0);
+        instr->ReplaceAllUsesWith(HBoundsCheck::cast(instr)->index());
+      }
+      instr = instr->next();
+    }
+  }
+}
+
+
 HInstruction* HGraphBuilder::AddInstruction(HInstruction* instr) {
   ASSERT(current_block() != NULL);
   current_block()->AddInstruction(instr);
@@ -3714,16 +3736,17 @@ HInstruction* HGraphBuilder::BuildLoadKeyedFastElement(HValue* object,
   bool is_array = (map->instance_type() == JS_ARRAY_TYPE);
   HLoadElements* elements = new(zone()) HLoadElements(object);
   HInstruction* length = NULL;
+  HInstruction* checked_key = NULL;
   if (is_array) {
     length = AddInstruction(new(zone()) HJSArrayLength(object));
-    AddInstruction(new(zone()) HBoundsCheck(key, length));
+    checked_key = AddInstruction(new(zone()) HBoundsCheck(key, length));
     AddInstruction(elements);
   } else {
     AddInstruction(elements);
     length = AddInstruction(new(zone()) HFixedArrayLength(elements));
-    AddInstruction(new(zone()) HBoundsCheck(key, length));
+    checked_key = AddInstruction(new(zone()) HBoundsCheck(key, length));
   }
-  return new(zone()) HLoadKeyedFastElement(elements, key);
+  return new(zone()) HLoadKeyedFastElement(elements, checked_key);
 }
 
 
@@ -3741,13 +3764,14 @@ HInstruction* HGraphBuilder::BuildLoadKeyedSpecializedArrayElement(
   AddInstruction(elements);
   HInstruction* length = new(zone()) HExternalArrayLength(elements);
   AddInstruction(length);
-  AddInstruction(new(zone()) HBoundsCheck(key, length));
+  HInstruction* checked_key =
+      AddInstruction(new(zone()) HBoundsCheck(key, length));
   HLoadExternalArrayPointer* external_elements =
       new(zone()) HLoadExternalArrayPointer(elements);
   AddInstruction(external_elements);
   HLoadKeyedSpecializedArrayElement* pixel_array_value =
       new(zone()) HLoadKeyedSpecializedArrayElement(
-          external_elements, key, expr->external_array_type());
+          external_elements, checked_key, expr->external_array_type());
   return pixel_array_value;
 }
 
@@ -3802,8 +3826,9 @@ HInstruction* HGraphBuilder::BuildStoreKeyedFastElement(HValue* object,
   } else {
     length = AddInstruction(new(zone()) HFixedArrayLength(elements));
   }
-  AddInstruction(new(zone()) HBoundsCheck(key, length));
-  return new(zone()) HStoreKeyedFastElement(elements, key, val);
+  HInstruction* checked_key =
+      AddInstruction(new(zone()) HBoundsCheck(key, length));
+  return new(zone()) HStoreKeyedFastElement(elements, checked_key, val);
 }
 
 
@@ -3822,7 +3847,8 @@ HInstruction* HGraphBuilder::BuildStoreKeyedSpecializedArrayElement(
   AddInstruction(elements);
   HInstruction* length = AddInstruction(
       new(zone()) HExternalArrayLength(elements));
-  AddInstruction(new(zone()) HBoundsCheck(key, length));
+  HInstruction* checked_key =
+      AddInstruction(new(zone()) HBoundsCheck(key, length));
   HLoadExternalArrayPointer* external_elements =
       new(zone()) HLoadExternalArrayPointer(elements);
   AddInstruction(external_elements);
@@ -3851,7 +3877,7 @@ HInstruction* HGraphBuilder::BuildStoreKeyedSpecializedArrayElement(
   }
   return new(zone()) HStoreKeyedSpecializedArrayElement(
       external_elements,
-      key,
+      checked_key,
       val,
       expr->external_array_type());
 }
@@ -3909,8 +3935,9 @@ bool HGraphBuilder::TryArgumentsAccess(Property* expr) {
     HInstruction* elements = AddInstruction(new(zone()) HArgumentsElements);
     HInstruction* length = AddInstruction(
         new(zone()) HArgumentsLength(elements));
-    AddInstruction(new(zone()) HBoundsCheck(key, length));
-    result = new(zone()) HAccessArgumentsAt(elements, length, key);
+    HInstruction* checked_key =
+        AddInstruction(new(zone()) HBoundsCheck(key, length));
+    result = new(zone()) HAccessArgumentsAt(elements, length, checked_key);
   }
   ast_context()->ReturnInstruction(result, expr->id());
   return true;
@@ -5023,8 +5050,9 @@ HStringCharCodeAt* HGraphBuilder::BuildStringCharCodeAt(HValue* string,
   AddInstruction(HCheckInstanceType::NewIsString(string));
   HStringLength* length = new(zone()) HStringLength(string);
   AddInstruction(length);
-  AddInstruction(new(zone()) HBoundsCheck(index, length));
-  return new(zone()) HStringCharCodeAt(string, index);
+  HInstruction* checked_index =
+      AddInstruction(new(zone()) HBoundsCheck(index, length));
+  return new(zone()) HStringCharCodeAt(string, checked_index);
 }
 
 

src/hydrogen.h

@@ -223,6 +223,7 @@ class HGraph: public ZoneObject {
   void Canonicalize();
   void OrderBlocks();
   void AssignDominators();
+  void ReplaceCheckedValues();
 
   // Returns false if there are phi-uses of the arguments-object
   // which are not supported by the optimizing compiler.

test/mjsunit/regress/regress-85177.js

+// Copyright 2011 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax
+
+gW=gH=175;
+g=[];
+
+for(var n=0; n<gW; n++){
+ var l=[];
+ for(var p=0; p<gH; p++){
+   l.push(1)
+ }
+ g.push(l)
+}
+
+function k(a,b){
+ if(a<0||b<0||a>=gW||b>=gH)
+   return 0;
+ return g[a][b];
+}
+
+function f(){
+ for(var a=[],f=0; f<gW; f++){
+   var b=[];
+   for(var h=0; h<gH; h++){
+     var e=0;
+     for(var i=-1; i<=1; i++)
+       for(var j=-1; j<=1; j++)
+          e+=k(f+i,h+j);
+     e=k(f,h)==1?1:0;
+     b.push(e)
+   }
+   a.push(b)
+ }
+}
+
+f();
+%OptimizeFunctionOnNextCall(f);
+f();
+