[llvm] [LLVM][SCEV] Look through common multiplicand when simplifying compares. (PR #141798)

[Nikita Popov via llvm-commits]

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@@ -10748,6 +10748,22 @@ bool ScalarEvolution::SimplifyICmpOperands(CmpPredicate &Pred, const SCEV *&LHS,
   if (Depth >= 3)
     return false;
 
+  // (X * Z) icmp (Y * Z) ==> X icmp Y
+  //     when neither multiply wraps and Z is positive.
+  if (isa<SCEVMulExpr>(LHS) && isa<SCEVMulExpr>(RHS)) {
+    const SCEVMulExpr *LMul = cast<SCEVMulExpr>(LHS);
+    const SCEVMulExpr *RMul = cast<SCEVMulExpr>(RHS);
+
+    if (LMul->getNumOperands() == 2 && RMul->getNumOperands() == 2 &&
+        LMul->getOperand(1) == RMul->getOperand(1) &&
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nikic wrote:

I think a simple case would be something like `range(0, 10) %a, range(10, 20) %b` and then `%a * vscale` and `%b * vscale`? I think in that case the common operand would be the first.

https://github.com/llvm/llvm-project/pull/141798