[llvm] [ValueTracking] Infer `exact` for `udiv` and `sdiv` (PR #126438)

[via llvm-commits]

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@@ -1804,11 +1811,19 @@ Instruction *InstCombinerImpl::visitSDiv(BinaryOperator &I) {
   }
 
   KnownBits KnownDividend = computeKnownBits(Op0, 0, &I);
-  if (!I.isExact() &&
-      (match(Op1, m_Power2(Op1C)) || match(Op1, m_NegatedPower2(Op1C))) &&
-      KnownDividend.countMinTrailingZeros() >= Op1C->countr_zero()) {
-    I.setIsExact();
-    return &I;
+  if (!I.isExact()) {
+
+    if ((match(Op1, m_Power2(Op1C)) || match(Op1, m_NegatedPower2(Op1C))) &&
+        KnownDividend.countMinTrailingZeros() >= Op1C->countr_zero()) {
+      I.setIsExact();
+      return &I;
+    }
+
+    // Infer `exact` from dominating conditions.
+    if (isKnownToBeAnExactDivFromConds(Op0, Op1, /*isSigned=*/true, &I)) {
+      I.setIsExact();
+      return &I;
+    }
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goldsteinn wrote:

Missing InstCombine tests?

https://github.com/llvm/llvm-project/pull/126438