Avoid copying flow-sensitive state when only a goto separates blocks.

src/hydrogen-flow-engine.h

 // Copyright 2013 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 120 matching lines @@
         // Must have visited all predecessors before this block.
         CheckPredecessorCount(block);
       }
 
       // Go through all instructions of the current block, updating the state.
       for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
         state = state->Process(it.Current(), zone_);
       }
 
       // Propagate the block state forward to all successor blocks.
-      for (int i = 0; i < block->end()->SuccessorCount(); i++) {
+      int max = block->end()->SuccessorCount();
+      for (int i = 0; i < max; i++) {
         HBasicBlock* succ = block->end()->SuccessorAt(i);
         IncrementPredecessorCount(succ);
         if (StateAt(succ) == NULL) {
           // This is the first state to reach the successor.
-          SetStateAt(succ, state->Copy(succ, zone_));
+          if (max == 1 && succ->predecessors()->length() == 1) {
+            // Optimization: successor can inherit this state.
+            SetStateAt(succ, state);
+          } else {
+            // Successor needs a copy of the state.
+            SetStateAt(succ, state->Copy(succ, zone_));
+          }
         } else {
           // Merge the current state with the state already at the successor.
           SetStateAt(succ, state->Merge(succ, StateAt(succ), zone_));
         }
       }
     }
   }
 
  private:
   // Computes and caches the loop effects for the loop which has the given
@@ skipping 69 matching lines @@
   ZoneList<int> pred_counts_;        // Finished predecessors (by block id).
 #endif
   ZoneList<State*> block_states_;    // Block states (by block id).
   ZoneList<Effects*> loop_effects_;  // Loop effects (by block id).
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_FLOW_ENGINE_H_