[BasicAA] Handle disjoint or as add in DecomposeGEP. (#78209)

This removes the MaskedValueIsZero check in decomposing geps in BasicAA, using
the isDisjoint flags instead. This relies on the disjoint flags being present
when AA is ran. The alternative would be to keep the old MaskedValueIsZero check
too if this causes issues.

1 files changed, 2 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index a4a0846..ab1ab10 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -393,10 +393,8 @@ static LinearExpression GetLinearExpression(
         // further.
         return Val;
       case Instruction::Or:
-        // X|C == X+C if all the bits in C are unset in X.  Otherwise we can't
-        // analyze it.
-        if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(),
-                               SimplifyQuery(DL, DT, AC, BOp)))
+        // X|C == X+C if it is disjoint.  Otherwise we can't analyze it.
+        if (!cast<PossiblyDisjointInst>(BOp)->isDisjoint())
           return Val;
 
         [[fallthrough]];