fix a common crash.

llvm-svn: 45614
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index 0665e87..dff60f6 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -180,6 +180,10 @@
     }
   }
   
+  // If there are no outputs, it must have side-effects.
+  if (SuccToSinkTo == 0)
+    return false;
+  
   // FIXME: Check that the instr doesn't have side effects etc.
   
   DEBUG(cerr << "Sink instr " << *MI);