[SelectionDAG] soften splat mask assert/unreachable (PR41535)

These are general queries, so they should not die when given
a degenerate input like an all undef mask. Callers should be
able to deal with an op that will eventually be simplified away.

llvm-svn: 358761

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 5689a152ca5..b2de2a4f343 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -9350,7 +9350,10 @@ bool ShuffleVectorSDNode::isSplatMask(const int *Mask, EVT VT) {
   for (i = 0, e = VT.getVectorNumElements(); i != e && Mask[i] < 0; ++i)
     /* search */;
 
-  assert(i != e && "VECTOR_SHUFFLE node with all undef indices!");
+  // If all elements are undefined, this shuffle can be considered a splat
+  // (although it should eventually get simplified away completely).
+  if (i == e)
+    return true;
 
   // Make sure all remaining elements are either undef or the same as the first
   // non-undef value.