[llvm-bugs] [Bug 27392] wrong code bug

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27392

Evgeny Stupachenko <evstupac at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Evgeny Stupachenko <evstupac at gmail.com> ---
evstupac committed rL267662: The patch fixes PR27392..

The patch fixes PR27392.
Summary:
 It is incorrect to compare TripCount (which is BECount + 1)

  with extraiters (or Count) to check if we should enter unrolled
  loop or not, because TripCount can potentially overflow
  (when BECount is max unsigned integer).

While comparing BECount with (Count - 1) is overflow safe and

  therefore correct.

Reviewer: hfinkel

Differential Revision: http://reviews.llvm.org/D19256

From: Evgeny Stupachenko <evstupac at gmail.com>


Files:
  /llvm/trunk/lib/Transforms/Utils/LoopUnrollRuntime.cpp
  /llvm/trunk/test/Transforms/LoopUnroll/AArch64/runtime-loop.ll
  /llvm/trunk/test/Transforms/LoopUnroll/runtime-loop.ll
  /llvm/trunk/test/Transforms/LoopUnroll/runtime-loop1.ll
  /llvm/trunk/test/Transforms/LoopUnroll/tripcount-overflow.ll

Users:
  evstupac (Author)

http://reviews.llvm.org/rL267662

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