Optimize away insertelement of an undef value. This shows up in

test/Codegen/ARM/reg_sequence.ll but it doesn't affect the generated code
because the coalescer cleans it up.  Radar 7998853.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104185 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 347024f0ae403b684a01cb6ea3fe27e9821dbe10..0ea46af2acf73393ef75c9ab120926e46ac22686 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6024,6 +6024,10 @@ SDValue DAGCombiner::visitINSERT_VECTOR_ELT(SDNode *N) {
   SDValue InVal = N->getOperand(1);
   SDValue EltNo = N->getOperand(2);
 
+  // If the inserted element is an UNDEF, just use the input vector.
+  if (InVal.getOpcode() == ISD::UNDEF)
+    return InVec;
+
   // If the invec is a BUILD_VECTOR and if EltNo is a constant, build a new
   // vector with the inserted element.
   if (InVec.getOpcode() == ISD::BUILD_VECTOR && isa<ConstantSDNode>(EltNo)) {