Improve our simple elimination of hole checks.

Currently we avoid checking for the hole value after array loads, if the
result is only used by instructions that definitely deoptimize in case
of the hole value (HChange instructions).

This change performs the same procedure for loading from deleteable/read-only
global variable where we can also avoid the check in the same cases.
Review URL: http://codereview.chromium.org/8054008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9453 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-arm.cc

@@ -1739,7 +1739,7 @@ LInstruction* LChunkBuilder::DoConstant(HConstant* instr) {
 
 LInstruction* LChunkBuilder::DoLoadGlobalCell(HLoadGlobalCell* instr) {
   LLoadGlobalCell* result = new LLoadGlobalCell;
-  return instr->check_hole_value()
+  return instr->RequiresHoleCheck()
       ? AssignEnvironment(DefineAsRegister(result))
       : DefineAsRegister(result);
 }
@@ -1756,7 +1756,7 @@ LInstruction* LChunkBuilder::DoStoreGlobalCell(HStoreGlobalCell* instr) {
   LOperand* temp = TempRegister();
   LOperand* value = UseTempRegister(instr->value());
   LInstruction* result = new LStoreGlobalCell(value, temp);
-  if (instr->check_hole_value()) result = AssignEnvironment(result);
+  if (instr->RequiresHoleCheck()) result = AssignEnvironment(result);
   return result;
 }
 

src/arm/lithium-codegen-arm.cc

@@ -2207,7 +2207,7 @@ void LCodeGen::DoLoadGlobalCell(LLoadGlobalCell* instr) {
   Register result = ToRegister(instr->result());
   __ mov(ip, Operand(Handle<Object>(instr->hydrogen()->cell())));
   __ ldr(result, FieldMemOperand(ip, JSGlobalPropertyCell::kValueOffset));
-  if (instr->hydrogen()->check_hole_value()) {
+  if (instr->hydrogen()->RequiresHoleCheck()) {
     __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
     __ cmp(result, ip);
     DeoptimizeIf(eq, instr->environment());
@@ -2239,7 +2239,7 @@ void LCodeGen::DoStoreGlobalCell(LStoreGlobalCell* instr) {
   // been deleted from the property dictionary. In that case, we need
   // to update the property details in the property dictionary to mark
   // it as no longer deleted.
-  if (instr->hydrogen()->check_hole_value()) {
+  if (instr->hydrogen()->RequiresHoleCheck()) {
     __ ldr(scratch2,
            FieldMemOperand(scratch, JSGlobalPropertyCell::kValueOffset));
     __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
@@ -2541,13 +2541,9 @@ void LCodeGen::DoLoadKeyedFastDoubleElement(
            Operand(FixedDoubleArray::kHeaderSize - kHeapObjectTag));
   }
 
-  if (instr->hydrogen()->RequiresHoleCheck()) {
-    // TODO(danno): If no hole check is required, there is no need to allocate
-    // elements into a temporary register, instead scratch can be used.
   __ ldr(scratch, MemOperand(elements, sizeof(kHoleNanLower32)));
   __ cmp(scratch, Operand(kHoleNanUpper32));
   DeoptimizeIf(eq, instr->environment());
-  }
 
   __ vldr(result, elements, 0);
 }

src/hydrogen-instructions.cc

@@ -1464,7 +1464,7 @@ void HLoadKeyedFastElement::PrintDataTo(StringStream* stream) {
 }
 
 
-bool HLoadKeyedFastElement::RequiresHoleCheck() const {
+bool HLoadKeyedFastElement::RequiresHoleCheck() {
   for (HUseIterator it(uses()); !it.Done(); it.Advance()) {
     HValue* use = it.value();
     if (!use->IsChange()) return true;
@@ -1481,11 +1481,6 @@ void HLoadKeyedFastDoubleElement::PrintDataTo(StringStream* stream) {
 }
 
 
-bool HLoadKeyedFastDoubleElement::RequiresHoleCheck() const {
-  return true;
-}
-
-
 void HLoadKeyedGeneric::PrintDataTo(StringStream* stream) {
   object()->PrintNameTo(stream);
   stream->Add("[");
@@ -1639,7 +1634,18 @@ void HStoreKeyedSpecializedArrayElement::PrintDataTo(
 
 void HLoadGlobalCell::PrintDataTo(StringStream* stream) {
   stream->Add("[%p]", *cell());
-  if (check_hole_value()) stream->Add(" (deleteable/read-only)");
+  if (!details_.IsDontDelete()) stream->Add(" (deleteable)");
+  if (details_.IsReadOnly()) stream->Add(" (read-only)");
+}
+
+
+bool HLoadGlobalCell::RequiresHoleCheck() {
+  if (details_.IsDontDelete() && !details_.IsReadOnly()) return false;
+  for (HUseIterator it(uses()); !it.Done(); it.Advance()) {
+    HValue* use = it.value();
+    if (!use->IsChange()) return true;
+  }
+  return false;
 }
 
 
@@ -1651,6 +1657,8 @@ void HLoadGlobalGeneric::PrintDataTo(StringStream* stream) {
 void HStoreGlobalCell::PrintDataTo(StringStream* stream) {
   stream->Add("[%p] = ", *cell());
   value()->PrintNameTo(stream);
+  if (!details_.IsDontDelete()) stream->Add(" (deleteable)");
+  if (details_.IsReadOnly()) stream->Add(" (read-only)");
 }
 
 

src/hydrogen-instructions.h

@@ -3201,15 +3201,15 @@ class HUnknownOSRValue: public HTemplateInstruction<0> {
 
 class HLoadGlobalCell: public HTemplateInstruction<0> {
  public:
-  HLoadGlobalCell(Handle<JSGlobalPropertyCell> cell, bool check_hole_value)
+  HLoadGlobalCell(Handle<JSGlobalPropertyCell> cell, PropertyDetails details)
-      : cell_(cell), check_hole_value_(check_hole_value) {
+      : cell_(cell), details_(details) {
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetFlag(kDependsOnGlobalVars);
   }
 
   Handle<JSGlobalPropertyCell>  cell() const { return cell_; }
-  bool check_hole_value() const { return check_hole_value_; }
+  bool RequiresHoleCheck();
 
   virtual void PrintDataTo(StringStream* stream);
 
@@ -3232,7 +3232,7 @@ class HLoadGlobalCell: public HTemplateInstruction<0> {
 
  private:
   Handle<JSGlobalPropertyCell> cell_;
-  bool check_hole_value_;
+  PropertyDetails details_;
 };
 
 
@@ -3273,15 +3273,17 @@ class HStoreGlobalCell: public HUnaryOperation {
  public:
   HStoreGlobalCell(HValue* value,
                    Handle<JSGlobalPropertyCell> cell,
-                   bool check_hole_value)
+                   PropertyDetails details)
       : HUnaryOperation(value),
         cell_(cell),
-        check_hole_value_(check_hole_value) {
+        details_(details) {
     SetFlag(kChangesGlobalVars);
   }
 
   Handle<JSGlobalPropertyCell> cell() const { return cell_; }
-  bool check_hole_value() const { return check_hole_value_; }
+  bool RequiresHoleCheck() {
+    return !details_.IsDontDelete() || details_.IsReadOnly();
+  }
 
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::Tagged();
@@ -3292,7 +3294,7 @@ class HStoreGlobalCell: public HUnaryOperation {
 
  private:
   Handle<JSGlobalPropertyCell> cell_;
-  bool check_hole_value_;
+  PropertyDetails details_;
 };
 
 
@@ -3543,7 +3545,7 @@ class HLoadKeyedFastElement: public HTemplateInstruction<2> {
 
   virtual void PrintDataTo(StringStream* stream);
 
-  bool RequiresHoleCheck() const;
+  bool RequiresHoleCheck();
 
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedFastElement)
 
@@ -3574,8 +3576,6 @@ class HLoadKeyedFastDoubleElement: public HTemplateInstruction<2> {
 
   virtual void PrintDataTo(StringStream* stream);
 
-  bool RequiresHoleCheck() const;
-
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedFastDoubleElement)
 
  protected:

src/hydrogen.cc

@@ -3168,8 +3168,8 @@ void HGraphBuilder::VisitVariableProxy(VariableProxy* expr) {
       if (type == kUseCell) {
         Handle<GlobalObject> global(info()->global_object());
         Handle<JSGlobalPropertyCell> cell(global->GetPropertyCell(&lookup));
-        bool check_hole = !lookup.IsDontDelete() || lookup.IsReadOnly();
+        HLoadGlobalCell* instr =
-        HLoadGlobalCell* instr = new(zone()) HLoadGlobalCell(cell, check_hole);
+            new(zone()) HLoadGlobalCell(cell, lookup.GetPropertyDetails());
         return ast_context()->ReturnInstruction(instr, expr->id());
       } else {
         HValue* context = environment()->LookupContext();
@@ -3630,10 +3630,10 @@ void HGraphBuilder::HandleGlobalVariableAssignment(Variable* var,
   LookupResult lookup;
   GlobalPropertyAccess type = LookupGlobalProperty(var, &lookup, true);
   if (type == kUseCell) {
-    bool check_hole = !lookup.IsDontDelete() || lookup.IsReadOnly();
     Handle<GlobalObject> global(info()->global_object());
     Handle<JSGlobalPropertyCell> cell(global->GetPropertyCell(&lookup));
-    HInstruction* instr = new(zone()) HStoreGlobalCell(value, cell, check_hole);
+    HInstruction* instr =
+        new(zone()) HStoreGlobalCell(value, cell, lookup.GetPropertyDetails());
     instr->set_position(position);
     AddInstruction(instr);
     if (instr->HasSideEffects()) AddSimulate(ast_id);

src/ia32/lithium-codegen-ia32.cc

@@ -2073,7 +2073,7 @@ void LCodeGen::DoReturn(LReturn* instr) {
 void LCodeGen::DoLoadGlobalCell(LLoadGlobalCell* instr) {
   Register result = ToRegister(instr->result());
   __ mov(result, Operand::Cell(instr->hydrogen()->cell()));
-  if (instr->hydrogen()->check_hole_value()) {
+  if (instr->hydrogen()->RequiresHoleCheck()) {
     __ cmp(result, factory()->the_hole_value());
     DeoptimizeIf(equal, instr->environment());
   }
@@ -2107,7 +2107,7 @@ void LCodeGen::DoStoreGlobalCell(LStoreGlobalCell* instr) {
   // been deleted from the property dictionary. In that case, we need
   // to update the property details in the property dictionary to mark
   // it as no longer deleted. We deoptimize in that case.
-  if (instr->hydrogen()->check_hole_value()) {
+  if (instr->hydrogen()->RequiresHoleCheck()) {
     __ cmp(FieldOperand(object, offset), factory()->the_hole_value());
     DeoptimizeIf(equal, instr->environment());
   }
@@ -2369,7 +2369,6 @@ void LCodeGen::DoLoadKeyedFastDoubleElement(
     LLoadKeyedFastDoubleElement* instr) {
   XMMRegister result = ToDoubleRegister(instr->result());
 
-  if (instr->hydrogen()->RequiresHoleCheck()) {
   int offset = FixedDoubleArray::kHeaderSize - kHeapObjectTag +
       sizeof(kHoleNanLower32);
   Operand hole_check_operand = BuildFastArrayOperand(
@@ -2378,7 +2377,6 @@ void LCodeGen::DoLoadKeyedFastDoubleElement(
       offset);
   __ cmp(hole_check_operand, Immediate(kHoleNanUpper32));
   DeoptimizeIf(equal, instr->environment());
-  }
 
   Operand double_load_operand = BuildFastArrayOperand(
       instr->elements(), instr->key(), FAST_DOUBLE_ELEMENTS,

src/ia32/lithium-ia32.cc

@@ -1785,7 +1785,7 @@ LInstruction* LChunkBuilder::DoConstant(HConstant* instr) {
 
 LInstruction* LChunkBuilder::DoLoadGlobalCell(HLoadGlobalCell* instr) {
   LLoadGlobalCell* result = new LLoadGlobalCell;
-  return instr->check_hole_value()
+  return instr->RequiresHoleCheck()
       ? AssignEnvironment(DefineAsRegister(result))
       : DefineAsRegister(result);
 }
@@ -1804,7 +1804,7 @@ LInstruction* LChunkBuilder::DoStoreGlobalCell(HStoreGlobalCell* instr) {
       new LStoreGlobalCell(UseTempRegister(instr->value()),
                            TempRegister(),
                            TempRegister());
-  return instr->check_hole_value() ? AssignEnvironment(result) : result;
+  return instr->RequiresHoleCheck() ? AssignEnvironment(result) : result;
 }
 
 

src/x64/lithium-codegen-x64.cc

@@ -2015,7 +2015,7 @@ void LCodeGen::DoLoadGlobalCell(LLoadGlobalCell* instr) {
     __ movq(result, instr->hydrogen()->cell(), RelocInfo::GLOBAL_PROPERTY_CELL);
     __ movq(result, Operand(result, 0));
   }
-  if (instr->hydrogen()->check_hole_value()) {
+  if (instr->hydrogen()->RequiresHoleCheck()) {
     __ CompareRoot(result, Heap::kTheHoleValueRootIndex);
     DeoptimizeIf(equal, instr->environment());
   }
@@ -2047,7 +2047,7 @@ void LCodeGen::DoStoreGlobalCell(LStoreGlobalCell* instr) {
   // been deleted from the property dictionary. In that case, we need
   // to update the property details in the property dictionary to mark
   // it as no longer deleted. We deoptimize in that case.
-  if (instr->hydrogen()->check_hole_value()) {
+  if (instr->hydrogen()->RequiresHoleCheck()) {
     __ CompareRoot(Operand(address, 0), Heap::kTheHoleValueRootIndex);
     DeoptimizeIf(equal, instr->environment());
   }
@@ -2316,7 +2316,6 @@ void LCodeGen::DoLoadKeyedFastDoubleElement(
     LLoadKeyedFastDoubleElement* instr) {
   XMMRegister result(ToDoubleRegister(instr->result()));
 
-  if (instr->hydrogen()->RequiresHoleCheck()) {
   int offset = FixedDoubleArray::kHeaderSize - kHeapObjectTag +
       sizeof(kHoleNanLower32);
   Operand hole_check_operand = BuildFastArrayOperand(
@@ -2326,7 +2325,6 @@ void LCodeGen::DoLoadKeyedFastDoubleElement(
       offset);
   __ cmpl(hole_check_operand, Immediate(kHoleNanUpper32));
   DeoptimizeIf(equal, instr->environment());
-  }
 
   Operand double_load_operand = BuildFastArrayOperand(
       instr->elements(), instr->key(), FAST_DOUBLE_ELEMENTS,

src/x64/lithium-x64.cc

@@ -1722,7 +1722,7 @@ LInstruction* LChunkBuilder::DoConstant(HConstant* instr) {
 
 LInstruction* LChunkBuilder::DoLoadGlobalCell(HLoadGlobalCell* instr) {
   LLoadGlobalCell* result = new LLoadGlobalCell;
-  return instr->check_hole_value()
+  return instr->RequiresHoleCheck()
       ? AssignEnvironment(DefineAsRegister(result))
       : DefineAsRegister(result);
 }
@@ -1740,7 +1740,7 @@ LInstruction* LChunkBuilder::DoStoreGlobalCell(HStoreGlobalCell* instr) {
       new LStoreGlobalCell(UseTempRegister(instr->value()),
                            TempRegister(),
                            TempRegister());
-  return instr->check_hole_value() ? AssignEnvironment(result) : result;
+  return instr->RequiresHoleCheck() ? AssignEnvironment(result) : result;
 }