add support for using vxor to build zero vectors.  This implements
Regression/CodeGen/PowerPC/vec_zero.ll

llvm-svn: 27059
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index abf7a79..5482e9a 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -101,6 +101,10 @@
     /// getVSPLTImmediate - Return the appropriate VSPLT* immediate to splat the
     /// specified isSplatShuffleMask VECTOR_SHUFFLE mask.
     unsigned getVSPLTImmediate(SDNode *N);
+    
+    /// isZeroVector - Return true if this build_vector is an all-zero vector.
+    ///
+    bool isZeroVector(SDNode *N);
   }
   
   class PPCTargetLowering : public TargetLowering {