Correct IDF calculator for ReverseIDF

Summary:
Need to use predecessors for reverse graph, successors for forward graph.
succ_iterator/pred_iterator are not compatible, this patch is all the work necessary to work around that (which is what everywhere else does).  Not sure if there is a better way, so cc'ing some random folks to take a gander :)

Reviewers: dblaikie, qcolombet, echristo

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18796

llvm-svn: 266718
diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp
index 82248d1..e873c9e 100644
--- a/llvm/lib/Transforms/Utils/MemorySSA.cpp
+++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp
@@ -304,7 +304,7 @@
   }
 
   // Determine where our MemoryPhi's should go
-  IDFCalculator IDFs(*DT);
+  ForwardIDFCalculator IDFs(*DT);
   IDFs.setDefiningBlocks(DefiningBlocks);
   IDFs.setLiveInBlocks(LiveInBlocks);
   SmallVector<BasicBlock *, 32> IDFBlocks;