TableGen: Allow conditional instruction pattern in multiclass.

Define a 'null_frag' SDPatternOperator node, which if referenced in an
instruction Pattern, results in the pattern being collapsed to be as-if
'[]' had been specified instead. This allows supporting a multiclass
definition where some instaniations have ISel patterns associated and
others do not.

For example,
multiclass myMulti<RegisterClass rc, SDPatternOperator OpNode = null_frag> {
  def _x : myI<(outs rc:), (ins rc:), []>;
  def _r : myI<(outs rc:), (ins rc:), [(set rc:, (OpNode rc:))]>;
}

defm foo : myMulti<GRa, not>;
defm bar : myMulti<GRb>;

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160333 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/include/llvm/Target/TargetSelectionDAG.td b/include/llvm/Target/TargetSelectionDAG.td
index 5f069801a6..ff006b609d 100644
--- a/include/llvm/Target/TargetSelectionDAG.td
+++ b/include/llvm/Target/TargetSelectionDAG.td
@@ -595,6 +595,13 @@ def not  : PatFrag<(ops node:$in), (xor node:$in, -1)>;
 def vnot : PatFrag<(ops node:$in), (xor node:$in, immAllOnesV)>;
 def ineg : PatFrag<(ops node:$in), (sub 0, node:$in)>;
 
+// null_frag - The null pattern operator is used in multiclass instantiations
+// which accept an SDPatternOperator for use in matching patterns for internal
+// definitions. When expanding a pattern, if the null fragment is referenced
+// in the expansion, the pattern is discarded and it is as-if '[]' had been
+// specified. This allows multiclasses to have the isel patterns be optional.
+def null_frag : SDPatternOperator;
+
 // load fragments.
 def unindexedload : PatFrag<(ops node:$ptr), (ld node:$ptr), [{
   return cast<LoadSDNode>(N)->getAddressingMode() == ISD::UNINDEXED;