@@ -2516,38 +2516,46 @@ Value *SCEVExpander::generateOverflowCheck(const SCEVAddRecExpr *AR,
25162516 // And select either 1. or 2. depending on whether step is positive or
25172517 // negative. If Step is known to be positive or negative, only create
25182518 // either 1. or 2.
2519- Value *Add = nullptr , *Sub = nullptr ;
2520- bool NeedPosCheck = !SE.isKnownNegative (Step);
2521- bool NeedNegCheck = !SE.isKnownPositive (Step);
2522-
2523- if (PointerType *ARPtrTy = dyn_cast<PointerType>(ARTy)) {
2524- StartValue = InsertNoopCastOfTo (
2525- StartValue, Builder.getInt8PtrTy (ARPtrTy->getAddressSpace ()));
2526- Value *NegMulV = Builder.CreateNeg (MulV);
2527- if (NeedPosCheck)
2528- Add = Builder.CreateGEP (Builder.getInt8Ty (), StartValue, MulV);
2529- if (NeedNegCheck)
2530- Sub = Builder.CreateGEP (Builder.getInt8Ty (), StartValue, NegMulV);
2531- } else {
2519+ auto ComputeEndCheck = [&]() -> Value * {
2520+ // Checking <u 0 is always false.
2521+ if (!Signed && Start->isZero () && SE.isKnownPositive (Step))
2522+ return ConstantInt::getFalse (Loc->getContext ());
2523+
2524+ Value *Add = nullptr , *Sub = nullptr ;
2525+ bool NeedPosCheck = !SE.isKnownNegative (Step);
2526+ bool NeedNegCheck = !SE.isKnownPositive (Step);
2527+
2528+ if (PointerType *ARPtrTy = dyn_cast<PointerType>(ARTy)) {
2529+ StartValue = InsertNoopCastOfTo (
2530+ StartValue, Builder.getInt8PtrTy (ARPtrTy->getAddressSpace ()));
2531+ Value *NegMulV = Builder.CreateNeg (MulV);
2532+ if (NeedPosCheck)
2533+ Add = Builder.CreateGEP (Builder.getInt8Ty (), StartValue, MulV);
2534+ if (NeedNegCheck)
2535+ Sub = Builder.CreateGEP (Builder.getInt8Ty (), StartValue, NegMulV);
2536+ } else {
2537+ if (NeedPosCheck)
2538+ Add = Builder.CreateAdd (StartValue, MulV);
2539+ if (NeedNegCheck)
2540+ Sub = Builder.CreateSub (StartValue, MulV);
2541+ }
2542+
2543+ Value *EndCompareLT = nullptr ;
2544+ Value *EndCompareGT = nullptr ;
2545+ Value *EndCheck = nullptr ;
25322546 if (NeedPosCheck)
2533- Add = Builder.CreateAdd (StartValue, MulV);
2547+ EndCheck = EndCompareLT = Builder.CreateICmp (
2548+ Signed ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, Add, StartValue);
25342549 if (NeedNegCheck)
2535- Sub = Builder.CreateSub (StartValue, MulV);
2536- }
2537-
2538- Value *EndCompareLT = nullptr ;
2539- Value *EndCompareGT = nullptr ;
2540- Value *EndCheck = nullptr ;
2541- if (NeedPosCheck)
2542- EndCheck = EndCompareLT = Builder.CreateICmp (
2543- Signed ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, Add, StartValue);
2544- if (NeedNegCheck)
2545- EndCheck = EndCompareGT = Builder.CreateICmp (
2546- Signed ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT, Sub, StartValue);
2547- if (NeedPosCheck && NeedNegCheck) {
2548- // Select the answer based on the sign of Step.
2549- EndCheck = Builder.CreateSelect (StepCompare, EndCompareGT, EndCompareLT);
2550- }
2550+ EndCheck = EndCompareGT = Builder.CreateICmp (
2551+ Signed ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT, Sub, StartValue);
2552+ if (NeedPosCheck && NeedNegCheck) {
2553+ // Select the answer based on the sign of Step.
2554+ EndCheck = Builder.CreateSelect (StepCompare, EndCompareGT, EndCompareLT);
2555+ }
2556+ return EndCheck;
2557+ };
2558+ Value *EndCheck = ComputeEndCheck ();
25512559
25522560 // If the backedge taken count type is larger than the AR type,
25532561 // check that we don't drop any bits by truncating it. If we are
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