[llvm] [SCEV] Directly use wrap flags in getUDivExpr (PR #217133)

[Nikita Popov via llvm-commits]

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@@ -3522,27 +3522,14 @@ const SCEV *ScalarEvolution::getUDivExpr(SCEVUse LHS, SCEVUse RHS) {
     if (!RHSC->getValue()->isZero()) {
       // Determine if the division can be folded into the operands of
       // its operands.
-      // TODO: Generalize this to non-constants by using known-bits information.
-      Type *Ty = LHS->getType();
-      unsigned LZ = RHSC->getAPInt().countl_zero();
-      unsigned MaxShiftAmt = getTypeSizeInBits(Ty) - LZ - 1;
-      // For non-power-of-two values, effectively round the value up to the
-      // nearest power of two.
-      if (!RHSC->getAPInt().isPowerOf2())
-        ++MaxShiftAmt;
-      IntegerType *ExtTy =
-        IntegerType::get(getContext(), getTypeSizeInBits(Ty) + MaxShiftAmt);
       if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS))
         if (const SCEVConstant *Step =
             dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this))) {
           // {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded.
           const APInt &StepInt = Step->getAPInt();
           const APInt &DivInt = RHSC->getAPInt();
-          if (!StepInt.urem(DivInt) &&
-              getZeroExtendExpr(AR, ExtTy) ==
-              getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
-                            getZeroExtendExpr(Step, ExtTy),
-                            AR->getLoop(), SCEV::FlagAnyWrap)) {
+          bool NoWrap = inferNoWrapViaConstantRanges(AR);
+          if (!StepInt.urem(DivInt) && NoWrap) {
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nikic wrote:

If I understand correctly, this code was previously looking for NUW, but now you're checking the weaker NW instead. Why?

https://github.com/llvm/llvm-project/pull/217133