[llvm] [InstCombine] Don't use dominating conditions to transform sub into xor. (PR #88566)

[via llvm-commits]

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@@ -2281,8 +2281,10 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
   if (match(Op0, m_APInt(Op0C))) {
     if (Op0C->isMask()) {
       // Turn this into a xor if LHS is 2^n-1 and the remaining bits are known
-      // zero.
-      KnownBits RHSKnown = computeKnownBits(Op1, 0, &I);
+      // zero. We don't use information from dominating conditions so this
+      // transform is easier to reverse if necessary.
+      KnownBits RHSKnown = llvm::computeKnownBits(
+          Op1, 0, SQ.getWithInstruction(&I).getWithoutDomCondCache());
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goldsteinn wrote:

Is there a motivating case for when we would need/want to?

https://github.com/llvm/llvm-project/pull/88566