[llvm] [SCEV] Fold ((-1 * C1) * D / C1) -> -1 * D. (PR #157555)

[Florian Hahn via llvm-commits]

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@@ -3217,15 +3217,19 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
       }
 
       // Try to fold (C1 * D /u C2) -> C1/C2 * D, if C1 and C2 are powers-of-2,
-      // D is a multiple of C2, and C1 is a multiple of C1.
+      // D is a multiple of C2, and C1 is a multiple of C2.
       const SCEV *D;
+      APInt C1V = LHSC->getAPInt();
+      // (C1 * D /u C2) == -1 * -C1 * D /u C2 when C1 != INT_MIN.
+      if (C1V.isNegative() && !C1V.isMinSignedValue())
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fhahn wrote:

Yeah it's a no-op, we would end up with `(-INT_MIN * D /u C2) == (-1 * -INT_MIN * D /u C2)`. Can change to use `abs()` if you prefer and remove the check?

https://github.com/llvm/llvm-project/pull/157555