Optimize away nop CONCAT_VECTOR nodes.
Optimize CONCAT_VECTOR nodes that merge EXTRACT_SUBVECTOR values that extract from the same vector.
rdar://13402653
PR15866
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180871 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 310da09..85f5df9 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9122,6 +9122,45 @@
if (ISD::allOperandsUndef(N))
return DAG.getUNDEF(N->getValueType(0));
+ // Type legalization of vectors and DAG canonicalization of SHUFFLE_VECTOR
+ // nodes often generate nop CONCAT_VECTOR nodes.
+ // Scan the CONCAT_VECTOR operands and look for a CONCAT operations that
+ // place the incoming vectors at the exact same location.
+ SDValue SingleSource = SDValue();
+ unsigned PartNumElem = N->getOperand(0).getValueType().getVectorNumElements();
+
+ for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+ SDValue Op = N->getOperand(i);
+
+ if (Op.getOpcode() == ISD::UNDEF)
+ continue;
+
+ // Check if this is the identity extract:
+ if (Op.getOpcode() != ISD::EXTRACT_SUBVECTOR)
+ return SDValue();
+
+ // Find the single incoming vector for the extract_subvector.
+ if (SingleSource.getNode()) {
+ if (Op.getOperand(0) != SingleSource)
+ return SDValue();
+ } else {
+ SingleSource = Op.getOperand(0);
+ }
+
+ unsigned IdentityIndex = i * PartNumElem;
+ ConstantSDNode *CS = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+ // The extract index must be constant.
+ if (!CS)
+ return SDValue();
+
+ // Check that we are reading from the identity index.
+ if (CS->getZExtValue() != IdentityIndex)
+ return SDValue();
+ }
+
+ if (SingleSource.getNode())
+ return SingleSource;
+
return SDValue();
}