[DAGCombine] narrowInsertExtractVectorBinOp - add CONCAT_VECTORS support

We already split extract_subvector(binop(insert_subvector(v,x),insert_subvector(w,y))) -> binop(x,y).

This patch adds support for extract_subvector(binop(concat_vectors(),concat_vectors())) cases as well.

In particular this means we don't have to wait for X86 lowering to convert concat_vectors to insert_subvector chains, which helps avoid some cases where demandedelts/combine calls occur too late to split large vector ops.

The fast-isel-store.ll load folding regression is annoying but I don't think is that critical.

Differential Revision: https://reviews.llvm.org/D63653

llvm-svn: 365785

1 files changed, 14 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 320db83566b..c7c31d8a5b9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -18002,11 +18002,21 @@ static SDValue narrowInsertExtractVectorBinOp(SDNode *Extract,
   SDValue Index = Extract->getOperand(1);
   EVT VT = Extract->getValueType(0);
 
+  // Helper that peeks through INSERT_SUBVECTOR/CONCAT_VECTORS to find
+  // if the source subvector is the same type as the one being extracted.
   auto GetSubVector = [VT, Index](SDValue V) -> SDValue {
-    if (V.getOpcode() != ISD::INSERT_SUBVECTOR ||
-        V.getOperand(1).getValueType() != VT || V.getOperand(2) != Index)
-      return SDValue();
-    return V.getOperand(1);
+    if (V.getOpcode() == ISD::INSERT_SUBVECTOR &&
+        V.getOperand(1).getValueType() == VT && V.getOperand(2) == Index) {
+      return V.getOperand(1);
+    }
+    auto *IndexC = dyn_cast<ConstantSDNode>(Index);
+    if (IndexC && V.getOpcode() == ISD::CONCAT_VECTORS &&
+        V.getOperand(0).getValueType() == VT &&
+        (IndexC->getZExtValue() % VT.getVectorNumElements()) == 0) {
+      uint64_t SubIdx = IndexC->getZExtValue() / VT.getVectorNumElements();
+      return V.getOperand(SubIdx);
+    }
+    return SDValue();
   };
   SDValue Sub0 = GetSubVector(Bop0);
   SDValue Sub1 = GetSubVector(Bop1);