[VectorCombine] Fold vector.interleave2 with two constant splats (llvm#125144)

If we're interleaving 2 constant splats, for instance `<vscale x 8 x
i32> <splat of 666>` and `<vscale x 8 x i32> <splat of 777>`, we can
create a larger splat `<vscale x 8 x i64> <splat of ((777 << 32) |
666)>` first before casting it back into `<vscale x 16 x i32>`.

Author: mshockwave

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

@@ -126,6 +126,7 @@ class VectorCombine {
   bool foldShuffleFromReductions(Instruction &I);
   bool foldCastFromReductions(Instruction &I);
   bool foldSelectShuffle(Instruction &I, bool FromReduction = false);
+  bool foldInterleaveIntrinsics(Instruction &I);
   bool shrinkType(Instruction &I);
 
   void replaceValue(Value &Old, Value &New) {
@@ -3204,6 +3205,47 @@ bool VectorCombine::foldInsExtVectorToShuffle(Instruction &I) {
   return true;
 }
 
+/// If we're interleaving 2 constant splats, for instance `<vscale x 8 x i32>
+/// <splat of 666>` and `<vscale x 8 x i32> <splat of 777>`, we can create a
+/// larger splat `<vscale x 8 x i64> <splat of ((777 << 32) | 666)>` first
+/// before casting it back into `<vscale x 16 x i32>`.
+bool VectorCombine::foldInterleaveIntrinsics(Instruction &I) {
+  const APInt *SplatVal0, *SplatVal1;
+  if (!match(&I, m_Intrinsic<Intrinsic::vector_interleave2>(
+                     m_APInt(SplatVal0), m_APInt(SplatVal1))))
+    return false;
+
+  LLVM_DEBUG(dbgs() << "VC: Folding interleave2 with two splats: " << I
+                    << "\n");
+
+  auto *VTy =
+      cast<VectorType>(cast<IntrinsicInst>(I).getArgOperand(0)->getType());
+  auto *ExtVTy = VectorType::getExtendedElementVectorType(VTy);
+  unsigned Width = VTy->getElementType()->getIntegerBitWidth();
+
+  // Just in case the cost of interleave2 intrinsic and bitcast are both
+  // invalid, in which case we want to bail out, we use <= rather
+  // than < here. Even they both have valid and equal costs, it's probably
+  // not a good idea to emit a high-cost constant splat.
+  if (TTI.getInstructionCost(&I, CostKind) <=
+      TTI.getCastInstrCost(Instruction::BitCast, I.getType(), ExtVTy,
+                           TTI::CastContextHint::None, CostKind)) {
+    LLVM_DEBUG(dbgs() << "VC: The cost to cast from " << *ExtVTy << " to "
+                      << *I.getType() << " is too high.\n");
+    return false;
+  }
+
+  APInt NewSplatVal = SplatVal1->zext(Width * 2);
+  NewSplatVal <<= Width;
+  NewSplatVal |= SplatVal0->zext(Width * 2);
+  auto *NewSplat = ConstantVector::getSplat(
+      ExtVTy->getElementCount(), ConstantInt::get(F.getContext(), NewSplatVal));
+
+  IRBuilder<> Builder(&I);
+  replaceValue(I, *Builder.CreateBitCast(NewSplat, I.getType()));
+  return true;
+}
+
 /// This is the entry point for all transforms. Pass manager differences are
 /// handled in the callers of this function.
 bool VectorCombine::run() {
@@ -3248,6 +3290,7 @@ bool VectorCombine::run() {
       MadeChange |= scalarizeBinopOrCmp(I);
       MadeChange |= scalarizeLoadExtract(I);
       MadeChange |= scalarizeVPIntrinsic(I);
+      MadeChange |= foldInterleaveIntrinsics(I);
     }
 
     if (Opcode == Instruction::Store)

llvm/test/Transforms/VectorCombine/RISCV/vector-interleave2-splat-e64.ll

@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -mtriple=riscv64 -mattr=+v %s -passes=vector-combine | FileCheck %s
+; RUN: opt -S -mtriple=riscv32 -mattr=+v %s -passes=vector-combine | FileCheck %s
+
+; We should not form a i128 vector.
+
+define void @interleave2_const_splat_nxv8i64(ptr %dst) {
+; CHECK-LABEL: define void @interleave2_const_splat_nxv8i64(
+; CHECK-SAME: ptr [[DST:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[INTERLEAVE2:%.*]] = call <vscale x 8 x i64> @llvm.vector.interleave2.nxv8i64(<vscale x 4 x i64> splat (i64 666), <vscale x 4 x i64> splat (i64 777))
+; CHECK-NEXT:    call void @llvm.vp.store.nxv8i64.p0(<vscale x 8 x i64> [[INTERLEAVE2]], ptr [[DST]], <vscale x 8 x i1> splat (i1 true), i32 88)
+; CHECK-NEXT:    ret void
+;
+  %interleave2 = call <vscale x 8 x i64> @llvm.vector.interleave2.nxv8i64(<vscale x 4 x i64> splat (i64 666), <vscale x 4 x i64> splat (i64 777))
+  call void @llvm.vp.store.nxv8i64.p0(<vscale x 8 x i64> %interleave2, ptr %dst, <vscale x 8 x i1> splat (i1 true), i32 88)
+  ret void
+}

llvm/test/Transforms/VectorCombine/RISCV/vector-interleave2-splat.ll

@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -mtriple=riscv64 -mattr=+v %s -passes=vector-combine | FileCheck %s
+; RUN: opt -S -mtriple=riscv32 -mattr=+v %s -passes=vector-combine | FileCheck %s
+; RUN: opt -S -mtriple=riscv64 -mattr=+zve32x %s -passes=vector-combine | FileCheck %s --check-prefix=ZVE32X
+
+define void @interleave2_const_splat_nxv16i32(ptr %dst) {
+; CHECK-LABEL: define void @interleave2_const_splat_nxv16i32(
+; CHECK-SAME: ptr [[DST:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    call void @llvm.vp.store.nxv16i32.p0(<vscale x 16 x i32> bitcast (<vscale x 8 x i64> splat (i64 3337189589658) to <vscale x 16 x i32>), ptr [[DST]], <vscale x 16 x i1> splat (i1 true), i32 88)
+; CHECK-NEXT:    ret void
+;
+; ZVE32X-LABEL: define void @interleave2_const_splat_nxv16i32(
+; ZVE32X-SAME: ptr [[DST:%.*]]) #[[ATTR0:[0-9]+]] {
+; ZVE32X-NEXT:    [[INTERLEAVE2:%.*]] = call <vscale x 16 x i32> @llvm.vector.interleave2.nxv16i32(<vscale x 8 x i32> splat (i32 666), <vscale x 8 x i32> splat (i32 777))
+; ZVE32X-NEXT:    call void @llvm.vp.store.nxv16i32.p0(<vscale x 16 x i32> [[INTERLEAVE2]], ptr [[DST]], <vscale x 16 x i1> splat (i1 true), i32 88)
+; ZVE32X-NEXT:    ret void
+;
+  %interleave2 = call <vscale x 16 x i32> @llvm.vector.interleave2.nxv16i32(<vscale x 8 x i32> splat (i32 666), <vscale x 8 x i32> splat (i32 777))
+  call void @llvm.vp.store.nxv16i32.p0(<vscale x 16 x i32> %interleave2, ptr %dst, <vscale x 16 x i1> splat (i1 true), i32 88)
+  ret void
+}