[PATCH] D93759: [VE] Expand single-element BUILD_VECTOR to INSERT_VECTOR_ELT

[Simon Moll via Phabricator via llvm-commits]

simoll updated this revision to Diff 314374.
simoll added a comment.

- NFC. Rebased.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D93759/new/

https://reviews.llvm.org/D93759

Files:
  llvm/lib/Target/VE/VEISelLowering.cpp
  llvm/test/CodeGen/VE/Vector/expand_single_elem_build_vec.ll


Index: llvm/test/CodeGen/VE/Vector/expand_single_elem_build_vec.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/VE/Vector/expand_single_elem_build_vec.ll
@@ -0,0 +1,14 @@
+; REQUIRES: asserts
+; RUN: not --crash llc %s -march=ve -mattr=+vpu -o /dev/null |& FileCheck %s
+
+; TODO: Replace this with a better test once insert_vector_elt isel is upstream.
+
+; CHECK:  t{{[0-9]+}}: v256i32 = insert_vector_elt undef:v256i32, [[VAL:t[0-9]+]], Constant:i64<42>
+; CHECK:  [[VAL]]: i32
+
+; Function Attrs: norecurse nounwind readnone
+; Check that a single-element insertion is lowered to a insert_vector_elt node for isel.
+define <256 x i32> @expand_single_elem_build_vec(i32 %x, i32 %y) {
+  %r = insertelement <256 x i32> undef, i32 %x, i32 42
+  ret <256 x i32> %r
+}
Index: llvm/lib/Target/VE/VEISelLowering.cpp
===================================================================
--- llvm/lib/Target/VE/VEISelLowering.cpp
+++ llvm/lib/Target/VE/VEISelLowering.cpp
@@ -1525,6 +1525,29 @@
                      MachinePointerInfo());
 }
 
+static bool getUniqueInsertion(SDNode *N, unsigned &UniqueIdx) {
+  if (!isa<BuildVectorSDNode>(N))
+    return false;
+  const auto *BVN = cast<BuildVectorSDNode>(N);
+
+  // Find first non-undef insertion.
+  unsigned Idx;
+  for (Idx = 0; Idx < BVN->getNumOperands(); ++Idx) {
+    auto ElemV = BVN->getOperand(Idx);
+    if (!ElemV->isUndef())
+      break;
+  }
+  // Remember insertion.
+  UniqueIdx = Idx++;
+  // Verify that all other insertions are undef.
+  for (; Idx < BVN->getNumOperands(); ++Idx) {
+    auto ElemV = BVN->getOperand(Idx);
+    if (!ElemV->isUndef())
+      return false;
+  }
+  return true;
+}
+
 static SDValue getSplatValue(SDNode *N) {
   if (auto *BuildVec = dyn_cast<BuildVectorSDNode>(N)) {
     return BuildVec->getSplatValue();
@@ -1538,6 +1561,17 @@
   unsigned NumEls = Op.getValueType().getVectorNumElements();
   MVT ElemVT = Op.getSimpleValueType().getVectorElementType();
 
+  // If there is just one element, expand to INSERT_VECTOR_ELT.
+  unsigned UniqueIdx;
+  if (getUniqueInsertion(Op.getNode(), UniqueIdx)) {
+    SDValue AccuV = DAG.getUNDEF(Op.getValueType());
+    auto ElemV = Op->getOperand(UniqueIdx);
+    SDValue IdxV = DAG.getConstant(UniqueIdx, DL, MVT::i64);
+    return DAG.getNode(ISD::INSERT_VECTOR_ELT, DL, Op.getValueType(), AccuV,
+                       ElemV, IdxV);
+  }
+
+  // Else emit a broadcast.
   if (SDValue ScalarV = getSplatValue(Op.getNode())) {
     // lower to VEC_BROADCAST
     MVT LegalResVT = MVT::getVectorVT(ElemVT, 256);


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