Fix use after free

[trentxintong]

Summary

Fix use after free in LoopUnswitch

[aprantl]

Good catch!

lib/Transforms/Scalar/LoopUnswitch.cpp

if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
         // If Succ has any successors with PHI nodes, update them to have
         // entries coming from Pred instead of Succ.
         Succ->replaceAllUsesWith(Pred);
 
         // Move all of the successor contents from Succ to Pred.
         Pred->getInstList().splice(BI->getIterator(), Succ->getInstList(),
                                    Succ->begin(), Succ->end());
         LPM->deleteSimpleAnalysisValue(BI, L);
-        BI->eraseFromParent();
         RemoveFromWorklist(BI, Worklist);
+        BI->eraseFromParent();
 
         // Remove Succ from the loop tree.
         LI->removeBlock(Succ);
         LPM->deleteSimpleAnalysisValue(Succ, L);
         Succ->eraseFromParent();
         ++NumSimplify;
         continue;
       }
 
       continue;
     }
   }
 }