[llvm] [OpenMPOpt] Fix incorrect end-of-kernel barrier removal (PR #65670)

[Daniel Woodworth via llvm-commits]

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@@ -2676,17 +2676,19 @@ struct AAExecutionDomainFunction : public AAExecutionDomain {
       if (!ED.EncounteredAssumes.empty() && !A.isModulePass())
         return;
 
-      // We can remove this barrier, if it is one, or all aligned barriers
-      // reaching the kernel end. In the latter case we can transitively work
-      // our way back until we find a barrier that guards a side-effect if we
-      // are dealing with the kernel end here.
+      // We can remove this barrier, if it is one, or aligned barriers reaching
+      // the kernel end (if CB is nullptr). Aligned barriers reaching the kernel
+      // end may have other successors besides the kernel end (especially if
+      // they're in loops) with non-local side-effects, so those barriers can
+      // only be removed if they also only reach the kernel end. If those
+      // barriers have other barriers reaching them, those can be transitively
+      // removed as well.
       if (CB) {
         DeletedBarriers.insert(CB);
         A.deleteAfterManifest(*CB);
         ++NumBarriersEliminated;
         Changed = ChangeStatus::CHANGED;
       } else if (!ED.AlignedBarriers.empty()) {
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dwoodwor-intel wrote:

@jdoerfert, is this issue with these barriers still being removed what's holding up this change? It looks to me like the fix for this should be separate from the fix I've implemented here to only remove barriers with a straight line to the kernel end, but is there something I'm missing?

https://github.com/llvm/llvm-project/pull/65670