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

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index a95424a1c9e455ffa4a9664770844aee75b28b7d..8443e928684be6c41c41712f0c914a97a61a65b7 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -934,11 +934,17 @@ class HGraphBuilder {
       : 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();
   }
@@ -965,11 +971,31 @@ class HGraphBuilder {
   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:
@@ -1332,6 +1358,7 @@ class HGraphBuilder {
   CompilationInfo* info_;
   HGraph* graph_;
   HBasicBlock* current_block_;
+  int no_side_effects_scope_environment_push_pop_delta_;
   int no_side_effects_scope_count_;
 };