Fix a tblgen problem handling variable_ops in tblgen instruction
definitions. This adds a new construct, "discard", for indicating
that a named node in the input matching pattern is to be discarded,
instead of corresponding to a node in the output pattern. This
allows tblgen to know where the arguments for the varaible_ops are
supposed to begin.

This fixes "rdar://5791600", whatever that is ;-).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51699 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/TargetSelectionDAG.td b/lib/Target/TargetSelectionDAG.td
index f194443..9def220 100644
--- a/lib/Target/TargetSelectionDAG.td
+++ b/lib/Target/TargetSelectionDAG.td
@@ -470,6 +470,7 @@
 def vtInt      : PatLeaf<(vt),  [{ return MVT::isInteger(N->getVT()); }]>;
 def vtFP       : PatLeaf<(vt),  [{ return MVT::isFloatingPoint(N->getVT()); }]>;
 
+def immAllZeros : PatLeaf<(imm), [{ return N->isNullValue(); }]>;
 def immAllOnes : PatLeaf<(imm), [{ return N->isAllOnesValue(); }]>;
 def immAllOnesV: PatLeaf<(build_vector), [{
   return ISD::isBuildVectorAllOnes(N);