[DAGCombiner] Teach createBuildVecShuffle to handle cases where input vectors are less than half of the output vector size.

This will be needed by a future commit to support sign/zero extending from v8i8 to v8i64 which requires a sign/zero_extend_vector_inreg to be created which requires v8i8 to be concatenated upto v64i8 and goes through this code.

llvm-svn: 284204

1 files changed, 9 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2ba23b3850c..da903764e10 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12983,11 +12983,15 @@ SDValue DAGCombiner::createBuildVecShuffle(SDLoc DL, SDNode *N,
   // We can't generate a shuffle node with mismatched input and output types.
   // Try to make the types match the type of the output.
   if (InVT1 != VT || InVT2 != VT) {
-    if (InVT1.getSizeInBits() * 2 == VT.getSizeInBits() && InVT1 == InVT2) {
-      // If both input vectors are exactly half the size of the output, concat
-      // them. If we have only one (non-zero) input, concat it with undef.
-      VecIn1 = DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, VecIn1,
-                           VecIn2.getNode() ? VecIn2 : DAG.getUNDEF(InVT1));
+    if ((VT.getSizeInBits() % InVT1.getSizeInBits() == 0) && InVT1 == InVT2) {
+      // If the output vector length is a multiple of both input lengths,
+      // we can concatenate them and pad the rest with undefs.
+      unsigned NumConcats = VT.getSizeInBits() / InVT1.getSizeInBits();
+      assert(NumConcats >= 2 && "Concat needs at least two inputs!");
+      SmallVector<SDValue, 2> ConcatOps(NumConcats, DAG.getUNDEF(InVT1));
+      ConcatOps[0] = VecIn1;
+      ConcatOps[1] = VecIn2 ? VecIn2 : DAG.getUNDEF(InVT1);
+      VecIn1 = DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, ConcatOps);
       VecIn2 = SDValue();
     } else if (InVT1.getSizeInBits() == VT.getSizeInBits() * 2) {
       if (!TLI.isExtractSubvectorCheap(VT, NumElems))