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| author | Andrew Trick <atrick@apple.com> | 2013-05-31 06:43:25 +0000 |
|---|---|---|
| committer | Andrew Trick <atrick@apple.com> | 2013-05-31 06:43:25 +0000 |
| commit | 616011418e7460f765469f6347417fa25b5b740b (patch) | |
| tree | 350eec7de69f9a4c5ebec3b0649726b4e71ab4cf /docs | |
| parent | affed7e11d9107285b1a9ffa2cf78a141fa27a3d (diff) | |
| download | llvm-616011418e7460f765469f6347417fa25b5b740b.tar.gz llvm-616011418e7460f765469f6347417fa25b5b740b.tar.bz2 llvm-616011418e7460f765469f6347417fa25b5b740b.tar.xz | |
Fix ScalarEvolution::ComputeExitLimitFromCond for 'or' conditions.
Fixes PR16130 - clang produces incorrect code with loop/expression at -O2.
This is a 2+ year old bug that's now holding up the release. It's a
case where we knowingly made aggressive assumptions about undefined
behavior. These assumptions are wrong when SCEV is computing a
subexpression that does not directly control the branch. With this
fix, we avoid making assumptions in those cases but still optimize the
common case. SCEV's trip count computation for exits controlled by
'or' expressions is now analagous to the trip count computation for
loops with multiple exits. I had already fixed the multiple exit case
to be conservative.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182989 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
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