[llvm] [SimplifyCFG] Skip threading if the target may have divergent branches (PR #100185)

[Sameer Sahasrabuddhe via llvm-commits]

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@@ -3246,7 +3246,12 @@ bool SimplifyCFGOpt::SpeculativelyExecuteBB(BranchInst *BI,
 }
 
 /// Return true if we can thread a branch across this block.
-static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
+static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB,
+                                               const TargetTransformInfo &TTI) {
+  // Skip threading if the branch may be divergent.
+  if (TTI.hasBranchDivergence(BB->getParent()))
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ssahasra wrote:

The TTI check has nothing to do with the specific block `BB`. A more natural check for this seems to be the outer function `FoldCondBranchOnValueKnownInPredecessor()`, where it can be an early return even before entering the `do-while` loop.

https://github.com/llvm/llvm-project/pull/100185