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

[Eli Friedman via llvm-commits]

efriedma added inline comments.


================
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)
----------------
pbarrio wrote:
> efriedma wrote:
> > 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.
> That was the first approach I tried, but it will unfold selects in cases where it is not necessary. I only want to unfold when there are two or more selects that use the same condition, so I need to check the condition's users instead of the select's uses.
I'm not following your response... "I.uses()" and "I.users()" are basically the same thing, except that "I.uses()" also gives you operand numbers.


https://reviews.llvm.org/D26450