diff options
author | Andrew Trick <atrick@apple.com> | 2013-10-25 21:35:52 +0000 |
---|---|---|
committer | Andrew Trick <atrick@apple.com> | 2013-10-25 21:35:52 +0000 |
commit | 8aa8cea3e964796187f8682e502a8446b3ce02e1 (patch) | |
tree | 35f1ab7b52c361b2082d72337ccc30234ebc760b /lib/Analysis | |
parent | 0f978ea45945bf3b8f2ce20f46d78dc840894623 (diff) | |
download | llvm-8aa8cea3e964796187f8682e502a8446b3ce02e1.tar.gz llvm-8aa8cea3e964796187f8682e502a8446b3ce02e1.tar.bz2 llvm-8aa8cea3e964796187f8682e502a8446b3ce02e1.tar.xz |
Fix LSR: don't normalize quadratic recurrences.
Partial fix for PR17459: wrong code at -O3 on x86_64-linux-gnu
(affecting trunk and 3.3)
ScalarEvolutionNormalization was attempting to normalize by adding and
subtracting strides. Chained recurrences don't work that way.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193437 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis')
-rw-r--r-- | lib/Analysis/ScalarEvolutionNormalization.cpp | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/lib/Analysis/ScalarEvolutionNormalization.cpp b/lib/Analysis/ScalarEvolutionNormalization.cpp index dd2ed4ff83..f110616844 100644 --- a/lib/Analysis/ScalarEvolutionNormalization.cpp +++ b/lib/Analysis/ScalarEvolutionNormalization.cpp @@ -119,11 +119,19 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) { const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap); switch (Kind) { case NormalizeAutodetect: - if (IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) { - const SCEV *TransformedStep = - TransformSubExpr(AR->getStepRecurrence(SE), - User, OperandValToReplace); - Result = SE.getMinusSCEV(Result, TransformedStep); + // Normalize this SCEV by subtracting the expression for the final step. + // We only allow affine AddRecs to be normalized, otherwise we would not + // be able to correctly denormalize. + // e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2} + // Normalized form: {-2,+,1,+,2} + // Denormalized form: {1,+,3,+,2} + // + // However, denormalization would use the a different step expression than + // normalization (see getPostIncExpr), generating the wrong final + // expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2} + if (AR->isAffine() && + IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) { + Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE)); Loops.insert(L); } #if 0 |