do not set the root to null if an argument is dead


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21188 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCISelPattern.cpp b/lib/Target/PowerPC/PPCISelPattern.cpp
index 566d79b..44e041a 100644
--- a/lib/Target/PowerPC/PPCISelPattern.cpp
+++ b/lib/Target/PowerPC/PPCISelPattern.cpp
@@ -203,8 +203,9 @@
       GPR_idx += delta;
     }
     ArgOffset += ObjSize;
+    if (newroot.Val)
+      DAG.setRoot(newroot.getValue(1));
     
-    DAG.setRoot(newroot.getValue(1));
     ArgValues.push_back(argt);
   }