[RISCV][TTI] Recognize CONCAT_VECTORS if a shufflevector mask is a

multiple insert subvector.

Author: HanKuanChen

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -343,6 +343,40 @@ RISCVTTIImpl::getConstantPoolLoadCost(Type *Ty,  TTI::TargetCostKind CostKind) {
                              /*AddressSpace=*/0, CostKind);
 }
 
+InstructionCost
+RISCVTTIImpl::isMultipleInsertSubvector(VectorType *Tp, ArrayRef<int> Mask,
+                                        TTI::TargetCostKind CostKind) {
+  if (!isa<FixedVectorType>(Tp))
+    return InstructionCost::getInvalid();
+  std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Tp);
+  if (LT.second.getScalarSizeInBits() == 1)
+    return InstructionCost::getInvalid();
+  // Try to guess SubTp.
+  for (unsigned SubVecSize = 1, E = Mask.size(); SubVecSize < E;
+       SubVecSize <<= 1) {
+    if (E % SubVecSize != 0)
+      continue;
+    SmallVector<int> RepeatedPattern(createSequentialMask(0, SubVecSize, 0));
+    bool Skip = false;
+    for (unsigned I = 0; I != E; I += SubVecSize)
+      if (!Mask.slice(I, SubVecSize).equals(RepeatedPattern)) {
+        Skip = true;
+        break;
+      }
+    if (Skip)
+      continue;
+    InstructionCost Cost = 0;
+    FixedVectorType *SubTp = FixedVectorType::get(
+        cast<FixedVectorType>(Tp)->getElementType(), SubVecSize);
+    // The cost of extraction from a subvector is 0 if the index is 0.
+    for (unsigned I = 0; I != E; I += SubVecSize)
+      Cost +=
+          getShuffleCost(TTI::SK_InsertSubvector, Tp, {}, CostKind, I, SubTp);
+    return Cost;
+  }
+  return InstructionCost::getInvalid();
+}
+
 static VectorType *getVRGatherIndexType(MVT DataVT, const RISCVSubtarget &ST,
                                         LLVMContext &C) {
   assert((DataVT.getScalarSizeInBits() != 8 ||
@@ -394,6 +428,10 @@ InstructionCost RISCVTTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
                                                         LT.second, CostKind);
           }
         }
+        if (InstructionCost Cost =
+                isMultipleInsertSubvector(Tp, Mask, CostKind);
+            Cost.isValid())
+          return Cost;
       }
       // vrgather + cost of generating the mask constant.
       // We model this for an unknown mask with a single vrgather.

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

@@ -55,6 +55,12 @@ class RISCVTTIImpl : public BasicTTIImplBase<RISCVTTIImpl> {
   /// type.
   InstructionCost getConstantPoolLoadCost(Type *Ty,
                                           TTI::TargetCostKind CostKind);
+
+  /// Return the cost if a shufflevector can be consist of multiple vslideup.
+  /// Otherwise, return InstructionCost::getInvalid().
+  InstructionCost isMultipleInsertSubvector(VectorType *Tp, ArrayRef<int> Mask,
+                                            TTI::TargetCostKind CostKind);
+
 public:
   explicit RISCVTTIImpl(const RISCVTargetMachine *TM, const Function &F)
       : BaseT(TM, F.getDataLayout()), ST(TM->getSubtargetImpl(F)),

llvm/test/Analysis/CostModel/RISCV/fixed-vector-insert-subvector.ll

@@ -3,9 +3,9 @@
 
 define void @test() {
 ; CHECK-LABEL: 'test'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 22 for instruction: %0 = shufflevector <8 x float> poison, <8 x float> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %0 = shufflevector <8 x float> poison, <8 x float> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %1 = shufflevector <4 x i16> poison, <4 x i16> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %2 = shufflevector <4 x float> poison, <4 x float> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %2 = shufflevector <4 x float> poison, <4 x float> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %3 = shufflevector <2 x i1> poison, <2 x i1> poison, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;

llvm/test/Transforms/SLPVectorizer/RISCV/remarks-insert-into-small-vector.ll

@@ -8,7 +8,7 @@
 ; YAML-NEXT:  Function:        test
 ; YAML-NEXT:  Args:
 ; YAML-NEXT:  - String:          'Stores SLP vectorized with cost '
-; YAML-NEXT:  - Cost:            '2'
+; YAML-NEXT:  - Cost:            '0'
 ; YAML-NEXT:  - String:          ' and with tree size '
 ; YAML-NEXT:  - TreeSize:        '7'
 

llvm/test/Transforms/SLPVectorizer/RISCV/revec-getGatherCost.ll

@@ -8,7 +8,7 @@
 ; YAML: Function:        test1
 ; YAML: Args:
 ; YAML:   - String:          'Stores SLP vectorized with cost '
-; YAML:   - Cost:            '6'
+; YAML:   - Cost:            '4'
 ; YAML:   - String:          ' and with tree size '
 ; YAML:   - TreeSize:        '5'