[llvm] [InstCombine] Simplify fractions when there is no overflow (PR #92949)

[via llvm-commits]

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@@ -1176,6 +1176,45 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
         Mul->setHasNoSignedWrap(OBO->hasNoSignedWrap());
         return Mul;
       }
+
+      // We can reduce expressions of things like * 150 / 100 to * 3 / 2
+      if (Op0->hasOneUse() && !C2->isZero() &&
+          !(IsSigned && C1->isMinSignedValue() && C2->isAllOnes())) {
+        assert(!C2->isMinSignedValue() &&
+               "This should have been folded away by InstSimplify");
+        APInt GCD = APIntOps::GreatestCommonDivisor(C1->abs(), C2->abs());
+        if (!GCD.isOne() && !GCD.isZero()) {
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goldsteinn wrote:

can GCD be zero?

https://github.com/llvm/llvm-project/pull/92949