[llvm] [InstCombine] Fold negation of unsigned div of non-negatives (PR #84951)

[via llvm-commits]

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@@ -2062,6 +2062,25 @@ static Instruction *foldSubOfMinMax(BinaryOperator &I,
   return nullptr;
 }
 
+/// Fold `sub 0, (udiv nneg X, nneg C)` into `sdiv nneg X, -C`
+static Instruction *foldNegationOfUDivOfNonNegatives(BinaryOperator &I,
+                                                     InstCombinerImpl &IC) {
+  Value *RHS = I.getOperand(1);
+  Value *X;
+  Constant *C;
+
+  const auto &SQ = IC.getSimplifyQuery().getWithInstruction(&I);
+  if (match(RHS, m_OneUse(m_UDiv(m_Value(X), m_Constant(C)))) &&
+      isKnownNonNegative(X, SQ) && isKnownNonNegative(C, SQ)) {
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goldsteinn wrote:

I don't think we look past `bitcast` when computing known bits for dom conditions.

https://github.com/llvm/llvm-project/pull/84951