Verify that no-side-effects scope does not add unsafe phis and does not change push-pop balance of …

src/hydrogen.h

 // 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 916 matching lines @@
   int position_;
 };
 
 
 class HGraphBuilder {
  public:
   explicit HGraphBuilder(CompilationInfo* info)
       : info_(info),
         graph_(NULL),
         current_block_(NULL),
+        no_side_effects_scope_environment_push_pop_delta_(0),
         no_side_effects_scope_count_(0) {}
   virtual ~HGraphBuilder() {}
 
   HBasicBlock* current_block() const { return current_block_; }
-  void set_current_block(HBasicBlock* block) { current_block_ = block; }
+  void set_current_block(HBasicBlock* block) {
+    // Conservatively disalow adding phis by disallowing changing the block
+    // as this class has no other bottlenecks for adding phis.
+    ASSERT(SafeToAddPhiInNoSideEffectsScope());
+    current_block_ = block;
+  }
   HEnvironment* environment() const {
     return current_block()->last_environment();
   }
   Zone* zone() const { return info_->zone(); }
   HGraph* graph() const { return graph_; }
   Isolate* isolate() const { return graph_->isolate(); }
 
   HGraph* CreateGraph();
 
   // Bailout environment manipulation.
   void Push(HValue* value) { environment()->Push(value); }
   HValue* Pop() { return environment()->Pop(); }
 
   // Adding instructions.
   HInstruction* AddInstruction(HInstruction* instr);
   void AddSimulate(BailoutId id,
                    RemovableSimulate removable = FIXED_SIMULATE);
   HBoundsCheck* AddBoundsCheck(
       HValue* index,
       HValue* length,
       BoundsCheckKeyMode key_mode = DONT_ALLOW_SMI_KEY,
       Representation r = Representation::None());
 
   HReturn* AddReturn(HValue* value);
 
   void IncrementInNoSideEffectsScope() {
+    if (no_side_effects_scope_count_ == 0) {
+      no_side_effects_scope_environment_push_pop_delta_ =
+          environment()->push_count() - environment()->pop_count();
+    }
     no_side_effects_scope_count_++;
   }
 
   void DecrementInNoSideEffectsScope() {
     no_side_effects_scope_count_--;
+    if (no_side_effects_scope_count_ == 0) {
+      // No-side-effects scope should not change push-pop delta.
+      ASSERT_EQ(no_side_effects_scope_environment_push_pop_delta_,
+                environment()->push_count() - environment()->pop_count());
+      no_side_effects_scope_environment_push_pop_delta_ = 0;
+    }
+  }
+
+  bool SafeToAddPhiInNoSideEffectsScope() {
+    // Pops and pushes after a simulate are not visible in LChunkBuilder.
+    // If the number of pops is greater than the number pushes then the
+    // environment in HGraphBuilder is shorter then the corresponding
+    // environment in LChunkBuilder. This causes non-observable phis
+    // to be pushed in the environment, which breaks deoptimization.
+    return no_side_effects_scope_count_ == 0 ||
+           no_side_effects_scope_environment_push_pop_delta_ >= 0;
   }
 
  protected:
   virtual bool BuildGraph() = 0;
 
   HBasicBlock* CreateBasicBlock(HEnvironment* env);
   HBasicBlock* CreateLoopHeaderBlock();
 
   HValue* BuildCheckNonSmi(HValue* object);
   HValue* BuildCheckMap(HValue* obj, Handle<Map> map);
@@ skipping 342 matching lines @@
                                         HValue* payload);
 
   HInstruction* BuildGetNativeContext(HValue* context);
   HInstruction* BuildGetArrayFunction(HValue* context);
 
  private:
   HGraphBuilder();
   CompilationInfo* info_;
   HGraph* graph_;
   HBasicBlock* current_block_;
+  int no_side_effects_scope_environment_push_pop_delta_;
   int no_side_effects_scope_count_;
 };
 
 
 class HOptimizedGraphBuilder: public HGraphBuilder, public AstVisitor {
  public:
   enum BreakType { BREAK, CONTINUE };
   enum SwitchType { UNKNOWN_SWITCH, SMI_SWITCH, STRING_SWITCH };
 
   // A class encapsulating (lazily-allocated) break and continue blocks for
@@ skipping 668 matching lines @@
   EmbeddedVector<char, 64> filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_