[llvm] [RISCV] Add lowerINSERT_SUBVECTORAsBUILD_VECTOR. (PR #110069)

[Han-Kuan Chen via llvm-commits]

https://github.com/HanKuanChen created https://github.com/llvm/llvm-project/pull/110069

None

>From 3f904b4a18de75a7b903caf5f77192b8a207f96e Mon Sep 17 00:00:00 2001
From: Han-Kuan Chen <hankuan.chen at sifive.com>
Date: Wed, 25 Sep 2024 10:51:02 -0700
Subject: [PATCH 1/2] [RISCV] Pre-commit test.

---
 .../rvv/fixed-vectors-insert-subvector.ll     | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
index e81f686a283032..2b7ba01b08e00e 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
@@ -894,3 +894,26 @@ define <4 x i32> @insert_extract_v8i32_v2i32_0(<2 x i32> %v) {
   %2 = call <4 x i32> @llvm.vector.extract.v4i32.v8i32(<8 x i32> %1, i64 0)
   ret <4 x i32> %2
 }
+
+define <16 x i32> @build_vector_insert(<16 x i32> %0) {
+; VLA-LABEL: build_vector_insert:
+; VLA:       # %bb.0: # %entry
+; VLA-NEXT:    vsetivli zero, 8, e32, m2, ta, ma
+; VLA-NEXT:    vmv.v.i v16, 0
+; VLA-NEXT:    vsetivli zero, 16, e32, m4, ta, ma
+; VLA-NEXT:    vslideup.vi v12, v16, 8
+; VLA-NEXT:    vsetivli zero, 8, e32, m4, tu, ma
+; VLA-NEXT:    vmv.v.v v12, v8
+; VLA-NEXT:    vmv4r.v v8, v12
+; VLA-NEXT:    ret
+;
+; VLS-LABEL: build_vector_insert:
+; VLS:       # %bb.0: # %entry
+; VLS-NEXT:    vsetivli zero, 8, e32, m2, ta, ma
+; VLS-NEXT:    vmv.v.i v10, 0
+; VLS-NEXT:    ret
+entry:
+  %1 = call <16 x i32> @llvm.vector.insert.v16f32.v8f32(<16 x i32> poison, <8 x i32> zeroinitializer, i64 8)
+  %2 = shufflevector <16 x i32> %0, <16 x i32> %1, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 24, i32 25, i32 26, i32 27, i32 28, i32 29, i32 30, i32 31>
+  ret <16 x i32> %2
+}

>From 7678090afb6a8061193b4fb2f1b17985744e5ae6 Mon Sep 17 00:00:00 2001
From: Han-Kuan Chen <hankuan.chen at sifive.com>
Date: Wed, 25 Sep 2024 10:10:27 -0700
Subject: [PATCH 2/2] [RISCV] Add lowerINSERT_SUBVECTORAsBUILD_VECTOR.

---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp   | 32 +++++++++++++++++++
 .../rvv/fixed-vectors-insert-subvector.ll     | 10 +++---
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index bf822eb2c6eeb5..0fe38839b7759a 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -10140,6 +10140,35 @@ SDValue RISCVTargetLowering::lowerVPREDUCE(SDValue Op,
       DAG.getConstantFP(APFloat::getNaN(ResVT.getFltSemantics()), DL, ResVT));
 }
 
+// Merge BUILD_VECTOR and insert_subvector into BUILD_VECTOR.
+// e.g.,
+// t7: v8i32 = BUILD_VECTOR 0, 0, 0, 0, 0, 0, 0, 0
+// t9: v16i32 = insert_subvector undef:v16i32, t7, i64<8>
+// ->
+// BUILD_VECTOR undef, undef, undef, undef, undef, undef, undef, undef, 0, 0, 0,
+// 0, 0, 0, 0, 0
+static SDValue lowerINSERT_SUBVECTORAsBUILD_VECTOR(SDValue Op,
+                                                   SelectionDAG &DAG) {
+  SDValue SubVec = Op.getOperand(1);
+  if (!Op.getOperand(0).isUndef())
+    return SDValue();
+  if (SubVec.getOpcode() != ISD::BUILD_VECTOR)
+    return SDValue();
+  SDLoc DL(Op);
+  MVT VecVT = Op.getSimpleValueType();
+  uint64_t InsertIndex = Op.getConstantOperandVal(2);
+  MVT SubVecVT = SubVec.getSimpleValueType();
+  MVT SubVecElementVT = SubVec.getOperand(0).getSimpleValueType();
+  unsigned SubVecNumElements = SubVecVT.getVectorNumElements();
+  SmallVector<SDValue> NewOps(VecVT.getVectorNumElements());
+  for (unsigned I = 0, E = VecVT.getVectorNumElements(); I != E; ++I)
+    if (I < InsertIndex || InsertIndex + SubVecNumElements <= I)
+      NewOps[I] = DAG.getUNDEF(SubVecElementVT);
+    else
+      NewOps[I] = SubVec.getOperand(I - InsertIndex);
+  return DAG.getNode(ISD::BUILD_VECTOR, DL, Op.getSimpleValueType(), NewOps);
+}
+
 SDValue RISCVTargetLowering::lowerINSERT_SUBVECTOR(SDValue Op,
                                                    SelectionDAG &DAG) const {
   SDValue Vec = Op.getOperand(0);
@@ -10191,6 +10220,9 @@ SDValue RISCVTargetLowering::lowerINSERT_SUBVECTOR(SDValue Op,
     }
   }
 
+  if (SDValue V = lowerINSERT_SUBVECTORAsBUILD_VECTOR(Op, DAG))
+    return V;
+
   // If the subvector vector is a fixed-length type and we don't know VLEN
   // exactly, we cannot use subregister manipulation to simplify the codegen; we
   // don't know which register of a LMUL group contains the specific subvector
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
index 2b7ba01b08e00e..347e7eeb6e8906 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
@@ -898,10 +898,8 @@ define <4 x i32> @insert_extract_v8i32_v2i32_0(<2 x i32> %v) {
 define <16 x i32> @build_vector_insert(<16 x i32> %0) {
 ; VLA-LABEL: build_vector_insert:
 ; VLA:       # %bb.0: # %entry
-; VLA-NEXT:    vsetivli zero, 8, e32, m2, ta, ma
-; VLA-NEXT:    vmv.v.i v16, 0
 ; VLA-NEXT:    vsetivli zero, 16, e32, m4, ta, ma
-; VLA-NEXT:    vslideup.vi v12, v16, 8
+; VLA-NEXT:    vmv.v.i v12, 0
 ; VLA-NEXT:    vsetivli zero, 8, e32, m4, tu, ma
 ; VLA-NEXT:    vmv.v.v v12, v8
 ; VLA-NEXT:    vmv4r.v v8, v12
@@ -909,8 +907,10 @@ define <16 x i32> @build_vector_insert(<16 x i32> %0) {
 ;
 ; VLS-LABEL: build_vector_insert:
 ; VLS:       # %bb.0: # %entry
-; VLS-NEXT:    vsetivli zero, 8, e32, m2, ta, ma
-; VLS-NEXT:    vmv.v.i v10, 0
+; VLS-NEXT:    vsetivli zero, 16, e32, m4, ta, ma
+; VLS-NEXT:    vmv.v.i v12, 0
+; VLS-NEXT:    vmv1r.v v10, v14
+; VLS-NEXT:    vmv1r.v v11, v15
 ; VLS-NEXT:    ret
 entry:
   %1 = call <16 x i32> @llvm.vector.insert.v16f32.v8f32(<16 x i32> poison, <8 x i32> zeroinitializer, i64 8)