[llvm-branch-commits] [llvm] [SimplifyCFG] Do not thread branches into uncontrolled convergent regions (PR #204958)

[Matt Arsenault via llvm-branch-commits]

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@@ -3619,6 +3673,14 @@ foldCondBranchOnValueKnownInPredecessorImpl(CondBrInst *BI, DomTreeUpdater *DTU,
     if (ReachesNonLocalUseBlocks.contains(RealDest))
       continue;
 
+    // Threading through a branch can bypass a reconvergence point. If the
+    // destination can execute an uncontrolled convergent operation before
+    // returning to this block, this may change the dynamic instance of that
+    // operation.
+    if (TTI.hasBranchDivergence(BB->getParent()) &&
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arsenm wrote:

Ugh. The semantics really shouldn't depend on this. We really need to get onto using convergence tokens for real 

https://github.com/llvm/llvm-project/pull/204958