[llvm] [InstCombine] Set disjoint flag when turning Add into Or. (PR #72702)

[via llvm-commits]

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@@ -1571,8 +1571,11 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
 
   // A+B --> A|B iff A and B have no bits set in common.
   WithCache<const Value *> LHSCache(LHS), RHSCache(RHS);
-  if (haveNoCommonBitsSet(LHSCache, RHSCache, SQ.getWithInstruction(&I)))
-    return BinaryOperator::CreateOr(LHS, RHS);
+  if (haveNoCommonBitsSet(LHSCache, RHSCache, SQ.getWithInstruction(&I))) {
+    auto *Or = BinaryOperator::CreateOr(LHS, RHS);
+    Or->setIsDisjoint();
+    return Or;
+  }
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goldsteinn wrote:

Think there are a few places where `xor` -> `or` where we could also add `disjoint`.

https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp#L4485
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp#L296

https://github.com/llvm/llvm-project/pull/72702