Fix code causing fallthrough warnings in the PPC back end.

llvm-svn: 320806
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index cf5c3e8..5e7a933 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -2224,6 +2224,7 @@
       if (CmpInGPR == ICGPR_Sext || CmpInGPR == ICGPR_SextI32 ||
           CmpInGPR == ICGPR_SextI64)
         return nullptr;
+      LLVM_FALLTHROUGH;
     case ISD::SIGN_EXTEND:
       if (CmpInGPR == ICGPR_Zext || CmpInGPR == ICGPR_ZextI32 ||
           CmpInGPR == ICGPR_ZextI64)