Index: lib/Transforms/Scalar/GVN.cpp
===================================================================
--- lib/Transforms/Scalar/GVN.cpp
+++ lib/Transforms/Scalar/GVN.cpp
@@ -2155,21 +2155,12 @@
 
   // Top-down walk of the dominator tree
   bool Changed = false;
-  // Save the blocks this function have before transformation begins. GVN may
-  // split critical edge, and hence may invalidate the RPO/DT iterator.
-  //
-  std::vector<BasicBlock *> BBVect;
-  BBVect.reserve(256);
   // Needed for value numbering with phi construction to work.
+  // RPOT walks the graph in its constructor and will not be invalidated during
+  // processBlock.
   ReversePostOrderTraversal<Function *> RPOT(&F);
-  for (ReversePostOrderTraversal<Function *>::rpo_iterator RI = RPOT.begin(),
-                                                           RE = RPOT.end();
-       RI != RE; ++RI)
-    BBVect.push_back(*RI);
-
-  for (std::vector<BasicBlock *>::iterator I = BBVect.begin(), E = BBVect.end();
-       I != E; I++)
-    Changed |= processBlock(*I);
+  for (BasicBlock *BB : RPOT)
+    Changed |= processBlock(BB);
 
   return Changed;
 }