diff options
Diffstat (limited to 'llvm/lib/Analysis/ScalarEvolution.cpp')
| -rw-r--r-- | llvm/lib/Analysis/ScalarEvolution.cpp | 22 |
1 files changed, 5 insertions, 17 deletions
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp index 22e361c22de..9e4eb111c2e 100644 --- a/llvm/lib/Analysis/ScalarEvolution.cpp +++ b/llvm/lib/Analysis/ScalarEvolution.cpp @@ -1274,25 +1274,13 @@ static const SCEV *getPreStartForExtend(const SCEVAddRecExpr *AR, Type *Ty, const SCEVAddRecExpr *PreAR = dyn_cast<SCEVAddRecExpr>( SE->getAddRecExpr(PreStart, Step, L, SCEV::FlagAnyWrap)); - // WARNING: FIXME: the optimization below assumes that a sign/zero-overflowing - // nsw/nuw operation is undefined behavior. This is strictly more aggressive - // than the interpretation of nsw in other parts of LLVM (for instance, they - // may unconditionally hoist nsw/nuw arithmetic through control flow). This - // logic needs to be revisited once we have a consistent semantics for poison - // values. - // - // "{S,+,X} is <nsw>/<nuw>" and "{S,+,X} is evaluated at least once" implies - // "S+X does not sign/unsign-overflow" (we'd have undefined behavior if it - // did). If `L->getExitingBlock() == L->getLoopLatch()` then `PreAR` (= - // {S,+,X}<nsw>/<nuw>) is evaluated every-time `AR` (= {S+X,+,X}) is - // evaluated, and hence within `AR` we are safe to assume that "S+X" will not - // sign/unsign-overflow. + // "{S,+,X} is <nsw>/<nuw>" and "the backedge is taken at least once" implies + // "S+X does not sign/unsign-overflow". // - BasicBlock *ExitingBlock = L->getExitingBlock(); - BasicBlock *LatchBlock = L->getLoopLatch(); - if (PreAR && PreAR->getNoWrapFlags(WrapType) && ExitingBlock != nullptr && - ExitingBlock == LatchBlock) + const SCEV *BECount = SE->getBackedgeTakenCount(L); + if (PreAR && PreAR->getNoWrapFlags(WrapType) && + !isa<SCEVCouldNotCompute>(BECount) && SE->isKnownPositive(BECount)) return PreStart; // 2. Direct overflow check on the step operation's expression. |
