[PATCH] D26450: [JumpThreading] Prevent non-deterministic use lists

[Eli Friedman via llvm-commits]

efriedma added a comment.

Yes, it's kind of hard to write a good unit-test for determinism, precisely because it isn't deterministic.  Maybe you could try something with opt -preserve-ll-uselistorder.  If you can't come up with something that makes sense, don't worry about it.



================
Comment at: lib/Transforms/Scalar/JumpThreading.cpp:2048
         if (auto *SI = dyn_cast<SelectInst>(U))
-          Selects.push_back(SI);
+          Selects.insert(SI);
       if (Selects.size() <= 1)
----------------
Looking at this a bit closer, there's another way you could write this: you can check whether the use is the condition of a select.  Something like:

    for (Use& U : I.uses()) {
      auto *SI = dyn_cast<SelectInst>(U.getUser());
      if (SI && U.getOperandNo() == 0)
        Selects.push_back(SI);
    }

That naturally avoids duplicates, and is probably a bit closer to your original intent.


https://reviews.llvm.org/D26450