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| author | Sanjoy Das <sanjoy@playingwithpointers.com> | 2015-02-09 18:34:55 +0000 |
|---|---|---|
| committer | Sanjoy Das <sanjoy@playingwithpointers.com> | 2015-02-09 18:34:55 +0000 |
| commit | bf5d870dfab3617f9dadb22e836503b88ba4c4af (patch) | |
| tree | a6ef5155b5199e9cfb5ee64c67ff64ca3101cdf2 /llvm/lib | |
| parent | 7eedd1c3815ebe8e2e31a0f70b8746e83e096e06 (diff) | |
| download | bcm5719-llvm-bf5d870dfab3617f9dadb22e836503b88ba4c4af.tar.gz bcm5719-llvm-bf5d870dfab3617f9dadb22e836503b88ba4c4af.zip | |
Bugfix: SCEV incorrectly marks certain add recurrences as nsw
When creating a scev for sext({X,+,Y}), scev checks if the expression
is equivalent to {sext X,+,zext Y}. If it can prove that, it also
tags the original {X,+,Y} as <nsw>, which is not correct.
In the test case I run `-scalar-evolution` twice because the bug
manifests only once SCEV has run through and seen the `sext`
expressions (and then does a in-place mutation on {X,+,Y}).
Differential Revision: http://reviews.llvm.org/D7495
llvm-svn: 228586
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Analysis/ScalarEvolution.cpp | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp index 649c6e0d575..9aefe8c33f7 100644 --- a/llvm/lib/Analysis/ScalarEvolution.cpp +++ b/llvm/lib/Analysis/ScalarEvolution.cpp @@ -1550,8 +1550,16 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op, getMulExpr(WideMaxBECount, getZeroExtendExpr(Step, WideTy))); if (SAdd == OperandExtendedAdd) { - // Cache knowledge of AR NSW, which is propagated to this AddRec. - const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNSW); + // If AR wraps around then + // + // abs(Step) * MaxBECount > unsigned-max(AR->getType()) + // => SAdd != OperandExtendedAdd + // + // Thus (AR is not NW => SAdd != OperandExtendedAdd) <=> + // (SAdd == OperandExtendedAdd => AR is NW) + + const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNW); + // Return the expression with the addrec on the outside. return getAddRecExpr(getSignExtendAddRecStart(AR, Ty, this), getZeroExtendExpr(Step, Ty), |
