[PATCH] D16570: [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader

[Chen Li via llvm-commits]

chenli created this revision.
chenli added a reviewer: sanjoy.
chenli added a subscriber: llvm-commits.

This is a revised version of D13974.

D13974 was committed but failed one lnt test. The bug was that we only checked the condition from loop exit's incoming block was a loop invariant. But there could be another condition from loop header to that incoming block not being a loop invariant. This would produce miscompiled code.

This patch fixes the issue by checking if the incoming block is loop header, and if not, don't perform the rewrite. The could be further improved by recursively checking all conditions leading to loop exit block, but I'd like to check in this simple version first and improve it with future patches.     

http://reviews.llvm.org/D16570

Files:
  lib/Transforms/Scalar/IndVarSimplify.cpp
  test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll
  test/Transforms/LoopUnroll/scevunroll.ll

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