[llvm] [LICM] Preserve Disjoint flag on OR when hoisting. (PR #140266)

[Eli Friedman via llvm-commits]

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@@ -2877,6 +2877,12 @@ static bool hoistBOAssociation(Instruction &I, Loop &L,
     if (auto *I = dyn_cast<Instruction>(Inv))
       I->setFastMathFlags(Intersect);
     NewBO->setFastMathFlags(Intersect);
+  } else if (Opcode == Instruction::Or) {
+    bool Disjoint = cast<PossiblyDisjointInst>(BO)->isDisjoint() &&
+                    cast<PossiblyDisjointInst>(BO0)->isDisjoint();
+    if (auto *I = dyn_cast<PossiblyDisjointInst>(Inv))
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efriedma-quic wrote:

It's not actually wrong with ConstantFolder, I guess, but the interaction is pretty subtle.  I've seen similar-looking code cause real issues.

Maybe it's enough to spell out that it's using ConstantFolder, and why it's getting used?

https://github.com/llvm/llvm-project/pull/140266