Merge r9778 from the bleeding_edge to the 3.6 branch.

src/hydrogen.cc

Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc	(revision 9791)
+++ src/hydrogen.cc	(working copy)
@@ -1487,6 +1487,9 @@
         block->block_id() < dominated->block_id() &&
         visited_on_paths_.Add(block->block_id())) {
       side_effects |= block_side_effects_[block->block_id()];
+      if (block->IsLoopHeader()) {
+        side_effects |= loop_side_effects_[block->block_id()];
+      }
       side_effects |= CollectSideEffectsOnPathsToDominatedBlock(
           dominator, block);
     }