[llvm] [SCEV] Add predicate in SolveLinEq to ensure B is a multiple of A. (PR #108777)

[Florian Hahn via llvm-commits]

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@@ -10137,8 +10140,17 @@ static const SCEV *SolveLinEquationWithOverflow(const APInt &A, const SCEV *B,
   //
   // B is divisible by D if and only if the multiplicity of prime factor 2 for B
   // is not less than multiplicity of this prime factor for D.
-  if (SE.getMinTrailingZeros(B) < Mult2)
-    return SE.getCouldNotCompute();
+  if (SE.getMinTrailingZeros(B) < Mult2) {
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fhahn wrote:

I stand corrected, the assertion actually uncovered a case where getMinTrailingZeros returns a worse result and I think catching this in getMinTrailingZeros would require matching a specific pattern (https://alive2.llvm.org/ce/z/t3A5X2)

I updated the code to check if the URem is zero if the trailing bits check failed, as we need to build the expression there already. Test is in `llvm/test/Analysis/ScalarEvolution/trip-count-urem.ll`

https://github.com/llvm/llvm-project/pull/108777