[PATCH] D29620: [JumpThreading] Thread through guards

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp:2076
+    if (Parent == Pred2->getSinglePredecessor())
+      if (BranchInst *BI = dyn_cast<BranchInst>(Parent->getTerminator()))
+        for (auto &I : *BB)
----------------
sanjoy wrote:
> mkazantsev wrote:
> > anna wrote:
> > > Hi Max, I think you need to check that branch is a conditional branch. Otherwise we can fail while trying to get the condition for the branch in `ThreadGuard` at line 2091.
> > You're right, I need to add this check here.
> I guess this is possible when `Pred1` and `Pred2` are the same, like:
> 
> 
> ```
> Parent:
>   br label %pred
> 
> pred:
>   switch ... 4 -> BB; 5 -> BB; ...
> 
> BB:
>   ...
> ```
> 
> 
> Are there other bits in this patch that are wrong in that situation?
> 
I think another example could be

  Parent:
    br %cond Pred, Pred

  Pred:
    br BB

  BB
    ...

So I would rather add both checks "branch is conditional" and pred1 != pred2.


Repository:
  rL LLVM

https://reviews.llvm.org/D29620