[llvm] [TTI][CostModel] Add cost modeling for expandload and compressstore intrinsics (PR #122882)

[Sergey Kachkov via llvm-commits]

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@@ -838,6 +838,43 @@ InstructionCost RISCVTTIImpl::getGatherScatterOpCost(
   return NumLoads * MemOpCost;
 }
 
+InstructionCost RISCVTTIImpl::getExpandCompressMemoryOpCost(
+    unsigned Opcode, Type *DataTy, bool VariableMask, Align Alignment,
+    TTI::TargetCostKind CostKind, const Instruction *I) {
+  bool IsLegal = (Opcode == Instruction::Store &&
+                  isLegalMaskedCompressStore(DataTy, Alignment)) ||
+                 (Opcode == Instruction::Load &&
+                  isLegalMaskedExpandLoad(DataTy, Alignment));
+  if (!IsLegal || CostKind != TTI::TCK_RecipThroughput)
+    return BaseT::getExpandCompressMemoryOpCost(Opcode, DataTy, VariableMask,
+                                                Alignment, CostKind, I);
+  // Example compressstore sequence:
+  // vsetivli        zero, 8, e32, m2, ta, ma (ignored)
+  // vcompress.vm    v10, v8, v0
+  // vcpop.m a1, v0
+  // vsetvli zero, a1, e32, m2, ta, ma
+  // vse32.v v10, (a0)
+  // Example expandload sequence:
+  // vsetivli        zero, 8, e8, mf2, ta, ma (ignored)
+  // vcpop.m a1, v0
+  // vsetvli zero, a1, e32, m2, ta, ma
+  // vle32.v v10, (a0)
+  // vsetivli        zero, 8, e32, m2, ta, ma
+  // viota.m v12, v0
+  // vrgather.vv     v8, v10, v12, v0.t
+  auto MemOpCost = getMemoryOpCost(Opcode, DataTy, Alignment, 0, CostKind);
+  auto LT = getTypeLegalizationCost(DataTy);
+  SmallVector<unsigned, 4> Opcodes{RISCV::VSETVLI};
+  if (VariableMask)
+    Opcodes.push_back(RISCV::VCPOP_M);
+  if (Opcode == Instruction::Store)
+    Opcodes.append({RISCV::VCOMPRESS_VM});
+  else
+    Opcodes.append({RISCV::VSETIVLI, RISCV::VIOTA_M, RISCV::VRGATHER_VV});
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skachkov-sc wrote:

In total we will have 3 vsetvli toogles for expand load, and only the first one is ignored (in hope that it can be optimized out). So I think we should add 2 vsetvli to the cost for this case (one VSETVLI is always added to the Opcodes list, and extra VSETIVLI is added in the case of Opcode == Load)

https://github.com/llvm/llvm-project/pull/122882