diff options
Diffstat (limited to 'llvm/lib/Transforms/Utils/SimplifyIndVar.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Utils/SimplifyIndVar.cpp | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp index 079ec7f..c7c0815 100644 --- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp @@ -1539,8 +1539,26 @@ bool WidenIV::widenWithVariantUse(WidenIV::NarrowIVDefUse DU) { ExtendKind ExtKind = getExtendKind(NarrowDef); bool CanSignExtend = ExtKind == SignExtended && OBO->hasNoSignedWrap(); bool CanZeroExtend = ExtKind == ZeroExtended && OBO->hasNoUnsignedWrap(); - if (!CanSignExtend && !CanZeroExtend) - return false; + auto AnotherOpExtKind = ExtKind; + if (!CanSignExtend && !CanZeroExtend) { + // Because InstCombine turns 'sub nuw' to 'add' losing the no-wrap flag, we + // will most likely not see it. Let's try to prove it. + if (OpCode != Instruction::Add) + return false; + if (ExtKind != ZeroExtended) + return false; + const SCEV *LHS = SE->getSCEV(OBO->getOperand(0)); + const SCEV *RHS = SE->getSCEV(OBO->getOperand(1)); + if (!SE->isKnownNegative(RHS)) + return false; + bool ProvedSubNUW = SE->isKnownPredicateAt( + ICmpInst::ICMP_UGE, LHS, SE->getNegativeSCEV(RHS), NarrowUse); + if (!ProvedSubNUW) + return false; + // In fact, our 'add' is 'sub nuw'. We will need to widen the 2nd operand as + // neg(zext(neg(op))), which is basically sext(op). + AnotherOpExtKind = SignExtended; + } // Verifying that Defining operand is an AddRec const SCEV *Op1 = SE->getSCEV(WideDef); @@ -1564,11 +1582,11 @@ bool WidenIV::widenWithVariantUse(WidenIV::NarrowIVDefUse DU) { Value *LHS = (NarrowUse->getOperand(0) == NarrowDef) ? WideDef : createExtendInst(NarrowUse->getOperand(0), WideType, - ExtKind, NarrowUse); + AnotherOpExtKind, NarrowUse); Value *RHS = (NarrowUse->getOperand(1) == NarrowDef) ? WideDef : createExtendInst(NarrowUse->getOperand(1), WideType, - ExtKind, NarrowUse); + AnotherOpExtKind, NarrowUse); auto *NarrowBO = cast<BinaryOperator>(NarrowUse); auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS, |