PR4317: Handle splits where the new block is unreachable correctly in

DominatorTreeBase::Split.

llvm-svn: 72810

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/include/llvm/Analysis/Dominators.h b/llvm/include/llvm/Analysis/Dominators.h
index b405f5b71ed..347e239d8ea 100644
--- a/llvm/include/llvm/Analysis/Dominators.h
+++ b/llvm/include/llvm/Analysis/Dominators.h
@@ -270,12 +270,17 @@ protected:
         NewBBIDom = PredBlocks[i];
         break;
       }
-    assert(i != PredBlocks.size() && "No reachable preds?");
+
+    // It's possible that none of the predecessors of NewBB are reachable;
+    // in that case, NewBB itself is unreachable, so nothing needs to be
+    // changed.
+    if (!NewBBIDom)
+      return;
+
     for (i = i + 1; i < PredBlocks.size(); ++i) {
       if (DT.isReachableFromEntry(PredBlocks[i]))
         NewBBIDom = DT.findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
     }
-    assert(NewBBIDom && "No immediate dominator found??");
 
     // Create the new dominator tree node... and set the idom of NewBB.
     DomTreeNodeBase<NodeT> *NewBBNode = DT.addNewBlock(NewBB, NewBBIDom);