[DAGCombiner] Fold extract_subvector of undef to undef. Fold away inserting undef...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293152 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 75f4a470212dc9e064949c6eeb6e4494c8db8683..17608b1f0a5753522976f4975654138116f9b8ce 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13880,6 +13880,10 @@ SDValue DAGCombiner::visitEXTRACT_SUBVECTOR(SDNode* N) {
   EVT NVT = N->getValueType(0);
   SDValue V = N->getOperand(0);
 
+  // Extract from UNDEF is UNDEF.
+  if (V.isUndef())
+    return DAG.getUNDEF(NVT);
+
   if (V->getOpcode() == ISD::CONCAT_VECTORS) {
     // Combine:
     //    (extract_subvec (concat V1, V2, ...), i)
@@ -14522,6 +14526,10 @@ SDValue DAGCombiner::visitINSERT_SUBVECTOR(SDNode *N) {
   SDValue N1 = N->getOperand(1);
   SDValue N2 = N->getOperand(2);
 
+  // If inserting an UNDEF, just return the original vector.
+  if (N1.isUndef())
+    return N0;
+
   // Combine INSERT_SUBVECTORs where we are inserting to the same index.
   // INSERT_SUBVECTOR( INSERT_SUBVECTOR( Vec, SubOld, Idx ), SubNew, Idx )
   // --> INSERT_SUBVECTOR( Vec, SubNew, Idx )