[llvm] [DFAJumpThreading] Try harder to avoid cycles in paths. (PR #169151)

[Hongyu Chen via llvm-commits]

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@@ -815,7 +819,12 @@ struct AllSwitchPaths {
 
     std::vector<ThreadingPath> TempList;
     for (const ThreadingPath &Path : PathsToPhiDef) {
+      SmallPtrSet<BasicBlock *, 32> PathSet(Path.getPath().begin(),
+                                            Path.getPath().end());
       for (const PathType &PathToSw : PathsToSwitchBB) {
+        if (any_of(llvm::drop_begin(PathToSw),
+                   [&](const BasicBlock *BB) { return PathSet.contains(BB); }))
+          continue;
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XChy wrote:

Is it necessary? IIUC, `VB` should record all the visited blocks before calculating `PathsToSwitchBB`, and `paths` don't consider these visited again.

https://github.com/llvm/llvm-project/pull/169151