[PATCH] ScalarEvolution incorrectly assumes that the start of certain add recurrences don't overflow

[Sanjoy Das]

================
Comment at: lib/Analysis/ScalarEvolution.cpp:1382
@@ -1368,1 +1381,3 @@
+  if (PreAR && PreAR->getNoWrapFlags(SCEV::FlagNSW) &&
+      L->getExitingBlock() == L->getLoopLatch())
     return PreStart;
----------------
hfinkel wrote:
> I think that you need to make sure that both L->getExitingBlock() and L->getLoopLatch() are not nullptr (which could happen if there is no unique loop latch and also no unique exiting block). Otherwise, LGTM.
> 
You're right, that was a slip on my part; will fix and check in.

Thanks for the review. :)

http://reviews.llvm.org/D7331

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