SDAGBuilder: Don't create an invalid iterator when there is only one switch case.

Found by libstdc++'s debug mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157522 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 0d37c62660d510c723f4723395411035b1f31ca7..f8cbcaa0d653cdb944553429b669a77e5c5d4406 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1984,10 +1984,10 @@ bool SelectionDAGBuilder::handleSmallSwitchRange(CaseRec& CR,
       }
     }
   }
-
   // Rearrange the case blocks so that the last one falls through if possible.
   Case &BackCase = *(CR.Range.second-1);
-  if (NextBlock && Default != NextBlock && BackCase.BB != NextBlock) {
+  if (Size > 1 &&
+      NextBlock && Default != NextBlock && BackCase.BB != NextBlock) {
     // The last case block won't fall through into 'NextBlock' if we emit the
     // branches in this order.  See if rearranging a case value would help.
     // We start at the bottom as it's the case with the least weight.