[llvm] [RISCV][TTI] Scale the cost of FP-Int conversion with LMUL (PR #87506)

[Luke Lau via llvm-commits]

================
@@ -1099,34 +1099,90 @@ InstructionCost RISCVTTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
     return Cost;
   }
   case ISD::FP_TO_SINT:
-  case ISD::FP_TO_UINT:
-    // For fp vector to mask, we use:
-    // vfncvt.rtz.x.f.w v9, v8
-    // vand.vi v8, v9, 1
-    // vmsne.vi v0, v8, 0
-    if (Dst->getScalarSizeInBits() == 1)
-      return 3;
-
-    if (std::abs(PowDiff) <= 1)
-      return 1;
+  case ISD::FP_TO_UINT: {
+    unsigned IsSigned = ISD == ISD::FP_TO_SINT;
+    unsigned FCVT = IsSigned ? RISCV::VFCVT_RTZ_X_F_V : RISCV::VFCVT_RTZ_XU_F_V;
+    unsigned FWCVT =
+        IsSigned ? RISCV::VFWCVT_RTZ_X_F_V : RISCV::VFWCVT_RTZ_XU_F_V;
+    unsigned FNCVT =
+        IsSigned ? RISCV::VFNCVT_RTZ_X_F_W : RISCV::VFNCVT_RTZ_XU_F_W;
+    unsigned SrcEltSize = Src->getScalarSizeInBits();
+    unsigned DstEltSize = Dst->getScalarSizeInBits();
+    InstructionCost Cost = 0;
+    if ((SrcEltSize == 16) &&
+        (!ST->hasVInstructionsF16() || ((DstEltSize / 2) > SrcEltSize))) {
+      // If the target only supports vfhmin or it is fp16-to-i64 conversion
+      // pre-widening to f32 and then convert f32 to integer
+      VectorType *VecF32Ty =
+          VectorType::get(Type::getFloatTy(Dst->getContext()),
+                          cast<VectorType>(Dst)->getElementCount());
+      std::pair<InstructionCost, MVT> VecF32LT =
+          getTypeLegalizationCost(VecF32Ty);
+      Cost +=
+          VecF32LT.first * getRISCVInstructionCost(RISCV::VFWCVT_F_F_V,
+                                                   VecF32LT.second, CostKind);
+      Cost += getCastInstrCost(Opcode, Dst, VecF32Ty, CCH, CostKind, I);
+      return Cost;
+    }
+    if (DstEltSize == SrcEltSize)
+      Cost += getRISCVInstructionCost(FCVT, DstLT.second, CostKind);
+    else if (DstEltSize > SrcEltSize)
+      Cost += getRISCVInstructionCost(FWCVT, DstLT.second, CostKind);
+    else { // (SrcEltSize > DstEltSize)
+      // First do a narrowing conversion to an integer half the size, then
+      // truncate if needed.
+      MVT ElementVT = MVT::getIntegerVT(SrcEltSize / 2);
+      MVT VecVT = DstLT.second.changeVectorElementType(ElementVT);
+      Cost += getRISCVInstructionCost(FNCVT, VecVT, CostKind);
+      if ((SrcEltSize / 2) > DstEltSize) {
+        Type *VecTy = EVT(VecVT).getTypeForEVT(Dst->getContext());
+        Cost +=
+            getCastInstrCost(Instruction::Trunc, Dst, VecTy, CCH, CostKind, I);
----------------
lukel97 wrote:

Ah ok, so it looks like after #101047 the types should still never be split. Can we add an assert somewhere below the new check that SrcLT.first & DstLT.first are always one?

https://github.com/llvm/llvm-project/pull/87506