[PATCH] [LoopReroll] Refactor most of reroll() into a helper class

[hfinkel at anl.gov]

With modifications suggested below, LGTM. Thanks!


REPOSITORY
  rL LLVM

================
Comment at: lib/Transforms/Scalar/LoopRerollPass.cpp:143
@@ +142,3 @@
+    // DAGRootTracker can access analyses such as SCEV.
+    friend class DAGRootTracker;
+
----------------
I'd prefer that we not do this just for access to the analysis variables. Just pass what is needed to the child class's constructor.

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Comment at: lib/Transforms/Scalar/LoopRerollPass.cpp:698
@@ +697,3 @@
+        if (Roots[Idx-1])
+          // No duplicates allowed.
+          return false;
----------------
IIRC, the current version deals with duplicated. I'm not sure this is necessary (one could certainly argue that CSE should take care of anything interesting). Please explain why, however, you're ignoring duplicates in this comment.

http://reviews.llvm.org/D7197

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