[llvm] [SCEV] Improve applyLoopGuards to support Mul (PR #83428)

[Nikita Popov via llvm-commits]

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@@ -15208,11 +15212,8 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
             auto *MulRHS = Mul->getOperand(1);
             if (isa<SCEVConstant>(MulLHS))
               std::swap(MulLHS, MulRHS);
-            if (auto *Div = dyn_cast<SCEVUDivExpr>(MulLHS))
-              if (Div->getOperand(1) == MulRHS) {
-                DividesBy = MulRHS;
-                return true;
-              }
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nikic wrote:

Right. I'm arguing that this is not correct. `X * constant` is not necessarily divisible by constant. This is only true if the multiplication has the nuw flag, or constant is a power of two.

https://github.com/llvm/llvm-project/pull/83428