[AArch64] Update costs for some fp16 converts

This updates the costs for FP16 converts, as some of them were pretty
high.

Differential Revision: https://reviews.llvm.org/D120771

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -1608,6 +1608,32 @@ InstructionCost AArch64TTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
                                                  SrcTy.getSimpleVT()))
     return AdjustCost(Entry->Cost);
 
+  static const TypeConversionCostTblEntry FP16Tbl[] = {
+      {ISD::FP_TO_SINT, MVT::v4i8, MVT::v4f16, 1}, // fcvtzs
+      {ISD::FP_TO_UINT, MVT::v4i8, MVT::v4f16, 1},
+      {ISD::FP_TO_SINT, MVT::v4i16, MVT::v4f16, 1}, // fcvtzs
+      {ISD::FP_TO_UINT, MVT::v4i16, MVT::v4f16, 1},
+      {ISD::FP_TO_SINT, MVT::v4i32, MVT::v4f16, 2}, // fcvtl+fcvtzs
+      {ISD::FP_TO_UINT, MVT::v4i32, MVT::v4f16, 2},
+      {ISD::FP_TO_SINT, MVT::v8i8, MVT::v8f16, 2}, // fcvtzs+xtn
+      {ISD::FP_TO_UINT, MVT::v8i8, MVT::v8f16, 2},
+      {ISD::FP_TO_SINT, MVT::v8i16, MVT::v8f16, 1}, // fcvtzs
+      {ISD::FP_TO_UINT, MVT::v8i16, MVT::v8f16, 1},
+      {ISD::FP_TO_SINT, MVT::v8i32, MVT::v8f16, 4}, // 2*fcvtl+2*fcvtzs
+      {ISD::FP_TO_UINT, MVT::v8i32, MVT::v8f16, 4},
+      {ISD::FP_TO_SINT, MVT::v16i8, MVT::v16f16, 3}, // 2*fcvtzs+xtn
+      {ISD::FP_TO_UINT, MVT::v16i8, MVT::v16f16, 3},
+      {ISD::FP_TO_SINT, MVT::v16i16, MVT::v16f16, 2}, // 2*fcvtzs
+      {ISD::FP_TO_UINT, MVT::v16i16, MVT::v16f16, 2},
+      {ISD::FP_TO_SINT, MVT::v16i32, MVT::v16f16, 8}, // 4*fcvtl+4*fcvtzs
+      {ISD::FP_TO_UINT, MVT::v16i32, MVT::v16f16, 8},
+  };
+
+  if (ST->hasFullFP16())
+    if (const auto *Entry = ConvertCostTableLookup(
+            FP16Tbl, ISD, DstTy.getSimpleVT(), SrcTy.getSimpleVT()))
+      return AdjustCost(Entry->Cost);
+
   return AdjustCost(
       BaseT::getCastInstrCost(Opcode, Dst, Src, CCH, CostKind, I));
 }