[PATCH] D113700: [AArch64] Improve costs for some conversions to fp16.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: dmgreen, ab, aemerson, samparker.
Herald added subscribers: hiraditya, kristof.beyls.
fhahn requested review of this revision.
Herald added a project: LLVM.

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 <https://reviews.llvm.org/rGc2ed9fd054797b2ba1fadb2e202e3afa5ec28d0b>.

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?


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D113700

Files:
  llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
  llvm/test/Analysis/CostModel/AArch64/cast.ll


Index: llvm/test/Analysis/CostModel/AArch64/cast.ll
===================================================================
--- llvm/test/Analysis/CostModel/AArch64/cast.ll
+++ llvm/test/Analysis/CostModel/AArch64/cast.ll
@@ -272,8 +272,8 @@
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r251 = sitofp <8 x i1> undef to <8 x half>
 ; NOFP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r252 = uitofp <8 x i8> undef to <8 x half>
 ; NOFP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r253 = sitofp <8 x i8> undef to <8 x half>
-; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r252 = uitofp <8 x i8> undef to <8 x half>
-; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r253 = sitofp <8 x i8> undef to <8 x half>
+; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r252 = uitofp <8 x i8> undef to <8 x half>
+; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %r253 = sitofp <8 x i8> undef to <8 x half>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r254 = uitofp <8 x i16> undef to <8 x half>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r255 = sitofp <8 x i16> undef to <8 x half>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %r256 = uitofp <8 x i32> undef to <8 x half>
@@ -284,8 +284,8 @@
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction:   %r261 = sitofp <16 x i1> undef to <16 x half>
 ; NOFP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction:   %r262 = uitofp <16 x i8> undef to <16 x half>
 ; NOFP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction:   %r263 = sitofp <16 x i8> undef to <16 x half>
-; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction:   %r262 = uitofp <16 x i8> undef to <16 x half>
-; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 3 for instruction:   %r263 = sitofp <16 x i8> undef to <16 x half>
+; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 4 for instruction:   %r262 = uitofp <16 x i8> undef to <16 x half>
+; FULLFP16-NEXT:  Cost Model: Found an estimated cost of 4 for instruction:   %r263 = sitofp <16 x i8> undef to <16 x half>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction:   %r264 = uitofp <16 x i16> undef to <16 x half>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction:   %r265 = sitofp <16 x i16> undef to <16 x half>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 6 for instruction:   %r266 = uitofp <16 x i32> undef to <16 x half>
Index: llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -1369,6 +1369,18 @@
                                                  SrcTy.getSimpleVT()))
     return AdjustCost(Entry->Cost);
 
+  if (ST->hasFullFP16()) {
+    static const TypeConversionCostTblEntry FP16ConversionTbl[] = {
+        {ISD::UINT_TO_FP, MVT::v8f16, MVT::v8i8, 2},
+        {ISD::SINT_TO_FP, MVT::v8f16, MVT::v8i8, 2},
+        {ISD::UINT_TO_FP, MVT::v16f16, MVT::v16i8, 4},
+        {ISD::SINT_TO_FP, MVT::v16f16, MVT::v16i8, 4},
+    };
+    if (const auto *Entry = ConvertCostTableLookup(
+            FP16ConversionTbl, ISD, DstTy.getSimpleVT(), SrcTy.getSimpleVT()))
+      return AdjustCost(Entry->Cost);
+  }
+
   return AdjustCost(
       BaseT::getCastInstrCost(Opcode, Dst, Src, CCH, CostKind, I));
 }


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