llvm-project

0856592f - Ensure `collectTransitivePredecessors` returns Pred only from the Loop. (#113831)

Ensure `collectTransitivePredecessors` returns Pred only from the Loop. (#113831) It's possible that we encounter Irreducible control flow, due to which, we may find that a few predecessors of BB are not a part of the CurLoop. Currently we crash in the function for such cases. This patch ensures that we only return Predecessors that are a part of CurLoop and gracefully ignore other Predecessors. For example, consider Irreducible IR of this form: ``` define i64 @baz() { bb: br label %bb1 bb1: ; preds = %bb3, %bb br label %bb3 bb2: ; No predecessors! br label %bb3 bb3: ; preds = %bb2, %bb1 %load = load ptr addrspace(1), ptr addrspace(1) null, align 8 br label %bb1 } ``` This crashes when `collectTransitivePredecessors` is called on the `%bb1<Header>, %bb3<latch>` loop, because the loop body has a predecessor `%bb2` which is not a part of the loop. See https://godbolt.org/z/E9fM1q3cT for the crash