From 19ea37059aaea8104ea6017abc9f1bbed610b7f2 Mon Sep 17 00:00:00 2001 From: Benjamin Kramer Date: Mon, 28 Oct 2013 07:30:06 +0000 Subject: SCEV: Make the final add of an inbounds GEP nuw if we know that the index is positive. We can't do this for the general case as saying a GEP with a negative index doesn't have unsigned wrap isn't valid for negative indices. %gep = getelementptr inbounds i32* %p, i64 -1 But an inbounds GEP cannot run past the end of address space. So we check for the very common case of a positive index and make GEPs derived from that NUW. Together with Andy's recent non-unit stride work this lets us analyze loops like void foo3(int *a, int *b) { for (; a < b; a++) {} } PR12375, PR12376. Differential Revision: http://llvm-reviews.chandlerc.com/D2033 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193514 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/ScalarEvolution.cpp | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) (limited to 'lib/Analysis') diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index ca959ab437..227f1de129 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -3088,15 +3088,20 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) { Flags = setFlags(Flags, SCEV::FlagNUW); if (OBO->hasNoSignedWrap()) Flags = setFlags(Flags, SCEV::FlagNSW); - } else if (const GEPOperator *GEP = - dyn_cast(BEValueV)) { + } else if (GEPOperator *GEP = dyn_cast(BEValueV)) { // If the increment is an inbounds GEP, then we know the address // space cannot be wrapped around. We cannot make any guarantee // about signed or unsigned overflow because pointers are // unsigned but we may have a negative index from the base - // pointer. - if (GEP->isInBounds()) + // pointer. We can guarantee that no unsigned wrap occurs if the + // indices form a positive value. + if (GEP->isInBounds()) { Flags = setFlags(Flags, SCEV::FlagNW); + + const SCEV *Ptr = getSCEV(GEP->getPointerOperand()); + if (isKnownPositive(getMinusSCEV(getSCEV(GEP), Ptr))) + Flags = setFlags(Flags, SCEV::FlagNUW); + } } const SCEV *StartVal = getSCEV(StartValueV); -- cgit v1.2.3