[AArch64] Improve costs for some conversions to fp16.

[fhahn]

Summary

Currently the cost model under-estimates the cost of certain
FP16 conversions.

This patch updates getCastInstrCost to return more accurate costs for
the cases improved in c2ed9fd05479.

Note that this does not fix the incorrect costs without FULLFP16 so far.
I'm not sure if there's a good generic way to estimate those costs
better, without explicitly adding a large number of combinations to the
table. Perhaps we could return a larger cost if we cannot match the
operation in any table?

[fhahn]

Just realized this was still hanging around.. Simplified after 47f4cd9c3dbfb383dd7 & ping

[dmgreen]

The new costs look good

llvm/test/Analysis/CostModel/AArch64/cast.ll

442–443

Use update_analyze_test_checks. You may find it is better to move the half checks to a separate function.

[fhahn]

Rebase after moving fp16 cast tests tp @fp16casts in 697f55e3682.

[fhahn]

llvm/test/Analysis/CostModel/AArch64/cast.ll

442–443

Good point, I moved the relevant fp16 casts in 697f55e3682.

[dmgreen]

Thanks. LGTM

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

static const TypeConversionCostTblEntry FP16Tbl[] = {
       {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},
+      {ISD::UINT_TO_FP, MVT::v8f16, MVT::v8i8, 2},   // ushll + ucvtf
+      {ISD::SINT_TO_FP, MVT::v8f16, MVT::v8i8, 2},   // sshll + scvtf
+      {ISD::UINT_TO_FP, MVT::v16f16, MVT::v16i8, 4}, // 2 * ushl(2) + 2 * ucvtf
+      {ISD::SINT_TO_FP, MVT::v16f16, MVT::v16i8, 4}, // 2 * sshl(2) + 2 * scvtf
   };
 
   if (ST->hasFullFP16())
     if (const auto *Entry = ConvertCostTableLookup(
             FP16Tbl, ISD, DstTy.getSimpleVT(), SrcTy.getSimpleVT()))
       return AdjustCost(Entry->Cost);
 
   return AdjustCost(

llvm/test/Analysis/CostModel/AArch64/cast.ll

 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 15 for instruction: %r241 = sitofp <16 x i1> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 39 for instruction: %r242 = uitofp <16 x i8> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 39 for instruction: %r243 = sitofp <16 x i8> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 38 for instruction: %r244 = uitofp <16 x i16> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 38 for instruction: %r245 = sitofp <16 x i16> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 38 for instruction: %r246 = uitofp <16 x i16> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 38 for instruction: %r247 = sitofp <16 x i16> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %r248 = uitofp <16 x i64> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %r249 = sitofp <16 x i64> undef to <16 x double>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret i32 undef
 ;
   %r30 = fptoui float undef to i1
   %r31 = fptosi float undef to i1
   %r32 = fptoui float undef to i8
   %r33 = fptosi float undef to i8
   %r34 = fptoui float undef to i16
   %r35 = fptosi float undef to i16
   %r36 = fptoui float undef to i32

 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r154 = fptoui <16 x half> undef to <16 x i16>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r155 = fptosi <16 x half> undef to <16 x i16>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %r156 = fptoui <16 x half> undef to <16 x i32>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %r157 = fptosi <16 x half> undef to <16 x i32>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 70 for instruction: %r158 = fptoui <16 x half> undef to <16 x i64>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 70 for instruction: %r159 = fptosi <16 x half> undef to <16 x i64>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r250 = uitofp <8 x i1> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r251 = sitofp <8 x i1> undef to <8 x half>
-; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r252 = uitofp <8 x i8> undef to <8 x half>
-; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r253 = sitofp <8 x i8> undef to <8 x half>
+; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r252 = uitofp <8 x i8> undef to <8 x half>
+; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r253 = sitofp <8 x i8> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r254 = uitofp <8 x i16> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r255 = sitofp <8 x i16> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r256 = uitofp <8 x i32> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r257 = sitofp <8 x i32> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 7 for instruction: %r258 = uitofp <8 x i64> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 7 for instruction: %r259 = sitofp <8 x i64> undef to <8 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r260 = uitofp <16 x i1> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r261 = sitofp <16 x i1> undef to <16 x half>
-; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r262 = uitofp <16 x i8> undef to <16 x half>
-; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r263 = sitofp <16 x i8> undef to <16 x half>
+; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %r262 = uitofp <16 x i8> undef to <16 x half>
+; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %r263 = sitofp <16 x i8> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r264 = uitofp <16 x i16> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r265 = sitofp <16 x i16> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 6 for instruction: %r266 = uitofp <16 x i32> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 6 for instruction: %r267 = sitofp <16 x i32> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 14 for instruction: %r268 = uitofp <16 x i64> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 14 for instruction: %r269 = sitofp <16 x i64> undef to <16 x half>
 ; CHECK-FP16-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;