[SCEV] Use or disjoint flag (#74467)

Use the disjoint flag to convert or to add instead of calling the
haveNoCommonBitsSet() ValueTracking query. This ensures that we can
reliably undo add -> or canonicalization, even in cases where the
necessary information has been lost or is too complex to reinfer in
SCEV.

I have updated the bulk of the test coverage to add the necessary
disjoint flags in advance.

1 files changed, 2 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 9670e53..451ae73 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5223,11 +5223,8 @@ static std::optional<BinaryOp> MatchBinaryOp(Value *V, const DataLayout &DL,
     return BinaryOp(Op);
 
   case Instruction::Or: {
-    // LLVM loves to convert `add` of operands with no common bits
-    // into an `or`. But SCEV really doesn't deal with `or` that well,
-    // so try extra hard to recognize this `or` as an `add`.
-    if (haveNoCommonBitsSet(Op->getOperand(0), Op->getOperand(1),
-                            SimplifyQuery(DL, &DT, &AC, CxtI)))
+    // Convert or disjoint into add nuw nsw.
+    if (cast<PossiblyDisjointInst>(Op)->isDisjoint())
       return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1),
                       /*IsNSW=*/true, /*IsNUW=*/true);
     return BinaryOp(Op);