[VPlan] Keep common flags during CSE. (#157664)

During CSE, we don't have to drop all poison-generating flags on
mis-match, we can keep the ones common on both recipes.

PR: https://github.com/llvm/llvm-project/pull/157664

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 78211524973e..6b122e19c016 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -2043,9 +2043,9 @@ void VPlanTransforms::cse(VPlan &Plan) {
         // V must dominate Def for a valid replacement.
         if (!VPDT.dominates(V->getParent(), VPBB))
           continue;
-        // Drop poison-generating flags when reusing a value.
+        // Only keep flags present on both V and Def.
         if (auto *RFlags = dyn_cast<VPRecipeWithIRFlags>(V))
-          RFlags->dropPoisonGeneratingFlags();
+          RFlags->intersectFlags(*cast<VPRecipeWithIRFlags>(Def));
         Def->replaceAllUsesWith(V);
         continue;
       }