DivergenceAnalysis: Fix crash with unreachable blocks

Unreachable blocks may not be in the dominator tree,
so don't crash on them.

llvm-svn: 268001

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/DivergenceAnalysis.cpp b/llvm/lib/Analysis/DivergenceAnalysis.cpp
index b30539f3b31..d38725ff0ac 100644
--- a/llvm/lib/Analysis/DivergenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DivergenceAnalysis.cpp
@@ -138,6 +138,11 @@ void DivergencePropagator::exploreSyncDependency(TerminatorInst *TI) {
   //   a2 = 2;
   // a = phi(a1, a2); // sync dependent on (tid < 5)
   BasicBlock *ThisBB = TI->getParent();
+
+  // Unreachable blocks may not be in the dominator tree.
+  if (!DT.isReachableFromEntry(ThisBB))
+    return;
+
   BasicBlock *IPostDom = PDT.getNode(ThisBB)->getIDom()->getBlock();
   if (IPostDom == nullptr)
     return;