[DAG] Remove isVectorClearMaskLegal() check from vector_build dagcombine

This check currently doesn't seem to do anything useful on any in-tree target:
On non-x86, it always evaluates to false, so we never hit the code path that
creates the shuffle with zero.
On x86, it just forwards to isShuffleMaskLegal(), which is a reasonable thing to
query in general, but doesn't make sense if only restricted to zero blends.

Differential Revision: https://reviews.llvm.org/D24625

llvm-svn: 282567

1 files changed, 0 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index bd882871246..d6f61851c29 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13064,13 +13064,6 @@ SDValue DAGCombiner::reduceBuildVecToShuffle(SDNode *N) {
     Mask[i] = Vec2Offset + ExtIndex;
   }
 
-  // Avoid introducing illegal shuffles with zero.
-  // TODO: This doesn't actually do anything smart at the moment.
-  // We should either delete this, or check legality for all the shuffles
-  // we create.
-  if (UsesZeroVector && !TLI.isVectorClearMaskLegal(Mask, VT))
-    return SDValue();
-
   // The type the input vectors may have changed above.
   InVT1 = VecIn1.getValueType();