[llvm] [SimplifyCFG] Consider preds to switch in `simplifyDuplicateSwitchArms` (PR #118955)

[Yingwei Zheng via llvm-commits]

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@@ -7575,8 +7573,10 @@ bool SimplifyCFGOpt::simplifyDuplicateSwitchArms(SwitchInst *SI,
       continue;
 
     // FIXME: This case needs some extra care because the terminators other than
-    // SI need to be updated.
-    if (BB->hasNPredecessorsOrMore(2))
+    // SI need to be updated. For now, consider only backedges to the SI.
+    if (pred_size(BB) > 4 || any_of(predecessors(BB), [&](BasicBlock *Pred) {
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dtcxzyw wrote:

It is used to avoid `O(N^2)` lookup. We may choose a larger threshold if the compile-time impact is negligible.


https://github.com/llvm/llvm-project/pull/118955