Fix error in postfix ++ in Crankshaft.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 73d3e498e5c2782eaeb36c6c368573365e81975e..22bc7ee8bfe72a975694e0cec7f773d9740353c4 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -1784,6 +1784,12 @@ void HGraph::InsertRepresentationChangeForUse(HValue* value,
 
   new_value->InsertBefore(next);
   use_value->SetOperandAt(use_index, new_value);
+
+  // The only purpose of a HForceRepresentation is to represent the value
+  // after the (possible) HChange instruction.  We make it disappear.
+  if (use_value->IsForceRepresentation()) {
+    use_value->DeleteAndReplaceWith(new_value);

[William Hesse, 2011/05/16 16:19:48]

We should be able to delete this copy.

[fschneider, 2011/05/17 11:03:15]

Yes, I think you can do it below and you only need to to DeleteAndReplaceWith
once.

+  }
 }
 
 
@@ -1803,6 +1809,12 @@ void HGraph::InsertRepresentationChangesForValue(HValue* value) {
     ASSERT(value->IsConstant());
     value->DeleteAndReplaceWith(NULL);
   }
+
+  // The only purpose of a HForceRepresentation is to represent the value
+  // after the (possible) HChange instruction.  We make it disappear.
+  if (value->IsForceRepresentation()) {
+    value->DeleteAndReplaceWith(HForceRepresentation::cast(value)->value());
+  }
 }
 
 
@@ -4699,20 +4711,32 @@ void HGraphBuilder::VisitNot(UnaryOperation* expr) {
 }
 
 
-HInstruction* HGraphBuilder::BuildIncrement(HValue* value,
-                                            bool increment,
+HInstruction* HGraphBuilder::BuildIncrement(bool returns_original_input,
                                             CountOperation* expr) {
-  HConstant* delta = increment
-      ? graph_->GetConstant1()
-      : graph_->GetConstantMinus1();
-  HInstruction* instr = new(zone()) HAdd(value, delta);
+  // The input to the count operation is on top of the expression stack.
   TypeInfo info = oracle()->IncrementType(expr);
   Representation rep = ToRepresentation(info);
   if (rep.IsTagged()) {
     rep = Representation::Integer32();
   }
+
+  if (returns_original_input) {
+    // If we need to return ToNumber(input), we force a representation change.

[fschneider, 2011/05/17 11:03:15]

maybe explain why:

// to have get a HValue for the return value here and the actual conversion is
inserted later.

+    HInstruction* number_input = new(zone()) HForceRepresentation(Pop(), rep);
+    AddInstruction(number_input);
+    Push(number_input);
+  }
+
+  // The addition has no side effects, so we do not need
+  // to simulate the expression stack after this instruction.
+  // Any later failures deopt to the load of the input or earlier.
+  HConstant* delta = (expr->op() == Token::INC)
+      ? graph_->GetConstant1()
+      : graph_->GetConstantMinus1();
+  HInstruction* instr = new(zone()) HAdd(Top(), delta);
   TraceRepresentation(expr->op(), info, instr, rep);
   instr->AssumeRepresentation(rep);
+  AddInstruction(instr);
   return instr;
 }
 
@@ -4725,18 +4749,25 @@ void HGraphBuilder::VisitCountOperation(CountOperation* expr) {
   VariableProxy* proxy = target->AsVariableProxy();
   Variable* var = proxy->AsVariable();
   Property* prop = target->AsProperty();
-  ASSERT(var == NULL || prop == NULL);
-  bool inc = expr->op() == Token::INC;
+  if (var == NULL && prop == NULL) {
+    return Bailout("invalid lhs in count operation");
+  }
+
+  // Match the full code generator stack by simulating an extra stack
+  // element for postfix operations in a non-effect context.  The return
+  // value is ToNumber(input).
+  bool returns_original_input =
+      expr->is_postfix() && !ast_context()->IsEffect();
+  HValue* input = NULL;  // The input to the count operation, after ToNumber.

[fschneider, 2011/05/17 11:03:15]

just say ToNumber(input)?

+  HValue* after = NULL;  // The result after incrementing or decrementing.
 
   if (var != NULL) {
+    // Argument of the count operation is a variable, not a property.
+    ASSERT(prop == NULL);
     CHECK_ALIVE(VisitForValue(target));
 
-    // Match the full code generator stack by simulating an extra stack
-    // element for postfix operations in a non-effect context.
-    bool has_extra = expr->is_postfix() && !ast_context()->IsEffect();
-    HValue* before = has_extra ? Top() : Pop();
-    HInstruction* after = BuildIncrement(before, inc, expr);
-    AddInstruction(after);
+    after = BuildIncrement(returns_original_input, expr);
+    input = returns_original_input ? Top() : Pop();
     Push(after);
 
     if (var->is_global()) {
@@ -4756,19 +4787,15 @@ void HGraphBuilder::VisitCountOperation(CountOperation* expr) {
     } else {
       return Bailout("lookup variable in count operation");
     }
-    Drop(has_extra ? 2 : 1);
-    ast_context()->ReturnValue(expr->is_postfix() ? before : after);
 
-  } else if (prop != NULL) {
+  } else {
+    // Argument of the count operation is a property.
+    ASSERT(prop != NULL);
     prop->RecordTypeFeedback(oracle());
 
     if (prop->key()->IsPropertyName()) {
       // Named property.
-
-      // Match the full code generator stack by simulating an extra stack
-      // element for postfix operations in a non-effect context.
-      bool has_extra = expr->is_postfix() && !ast_context()->IsEffect();
-      if (has_extra) Push(graph_->GetConstantUndefined());
+      if (returns_original_input) Push(graph_->GetConstantUndefined());
 
       CHECK_ALIVE(VisitForValue(prop->obj()));
       HValue* obj = Top();
@@ -4784,11 +4811,8 @@ void HGraphBuilder::VisitCountOperation(CountOperation* expr) {
       PushAndAdd(load);
       if (load->HasSideEffects()) AddSimulate(expr->CountId());
 
-      HValue* before = Pop();
-      // There is no deoptimization to after the increment, so we don't need
-      // to simulate the expression stack after this instruction.
-      HInstruction* after = BuildIncrement(before, inc, expr);
-      AddInstruction(after);
+      after = BuildIncrement(returns_original_input, expr);
+      input = Pop();
 
       HInstruction* store = BuildStoreNamed(obj, after, prop);
       AddInstruction(store);
@@ -4797,19 +4821,12 @@ void HGraphBuilder::VisitCountOperation(CountOperation* expr) {
       // of the operation, and the placeholder with the original value if
       // necessary.
       environment()->SetExpressionStackAt(0, after);
-      if (has_extra) environment()->SetExpressionStackAt(1, before);
+      if (returns_original_input) environment()->SetExpressionStackAt(1, input);
       if (store->HasSideEffects()) AddSimulate(expr->AssignmentId());
-      Drop(has_extra ? 2 : 1);
-
-      ast_context()->ReturnValue(expr->is_postfix() ? before : after);
 
-    } else {
+   } else {
       // Keyed property.
-
-      // Match the full code generator stack by simulate an extra stack element
-      // for postfix operations in a non-effect context.
-      bool has_extra = expr->is_postfix() && !ast_context()->IsEffect();
-      if (has_extra) Push(graph_->GetConstantUndefined());
+      if (returns_original_input) Push(graph_->GetConstantUndefined());
 
       CHECK_ALIVE(VisitForValue(prop->obj()));
       CHECK_ALIVE(VisitForValue(prop->key()));
@@ -4820,11 +4837,8 @@ void HGraphBuilder::VisitCountOperation(CountOperation* expr) {
       PushAndAdd(load);
       if (load->HasSideEffects()) AddSimulate(expr->CountId());
 
-      HValue* before = Pop();
-      // There is no deoptimization to after the increment, so we don't need
-      // to simulate the expression stack after this instruction.
-      HInstruction* after = BuildIncrement(before, inc, expr);
-      AddInstruction(after);
+      after = BuildIncrement(returns_original_input, expr);
+      input = Pop();
 
       expr->RecordTypeFeedback(oracle());
       HInstruction* store = BuildStoreKeyed(obj, key, after, expr);
@@ -4835,16 +4849,13 @@ void HGraphBuilder::VisitCountOperation(CountOperation* expr) {
       // original value if necessary.
       Drop(1);
       environment()->SetExpressionStackAt(0, after);
-      if (has_extra) environment()->SetExpressionStackAt(1, before);
+      if (returns_original_input) environment()->SetExpressionStackAt(1, input);
       if (store->HasSideEffects()) AddSimulate(expr->AssignmentId());
-      Drop(has_extra ? 2 : 1);
-
-      ast_context()->ReturnValue(expr->is_postfix() ? before : after);
     }
-
-  } else {
-    return Bailout("invalid lhs in count operation");
   }
+
+  Drop(returns_original_input ? 2 : 1);
+  ast_context()->ReturnValue(expr->is_postfix() ? input : after);
 }