[llvm] [AArch64] Add better fcmp costs for expanded predicates (PR #147940)

[Sam Tebbs via llvm-commits]

================
@@ -4308,63 +4307,80 @@ InstructionCost AArch64TTIImpl::getCmpSelInstrCost(
         return LT.first;
     }
 
-    static const TypeConversionCostTblEntry
-    VectorSelectTbl[] = {
-      { ISD::SELECT, MVT::v2i1, MVT::v2f32, 2 },
-      { ISD::SELECT, MVT::v2i1, MVT::v2f64, 2 },
-      { ISD::SELECT, MVT::v4i1, MVT::v4f32, 2 },
-      { ISD::SELECT, MVT::v4i1, MVT::v4f16, 2 },
-      { ISD::SELECT, MVT::v8i1, MVT::v8f16, 2 },
-      { ISD::SELECT, MVT::v16i1, MVT::v16i16, 16 },
-      { ISD::SELECT, MVT::v8i1, MVT::v8i32, 8 },
-      { ISD::SELECT, MVT::v16i1, MVT::v16i32, 16 },
-      { ISD::SELECT, MVT::v4i1, MVT::v4i64, 4 * AmortizationCost },
-      { ISD::SELECT, MVT::v8i1, MVT::v8i64, 8 * AmortizationCost },
-      { ISD::SELECT, MVT::v16i1, MVT::v16i64, 16 * AmortizationCost }
-    };
+    static const TypeConversionCostTblEntry VectorSelectTbl[] = {
+        {Instruction::Select, MVT::v2i1, MVT::v2f32, 2},
+        {Instruction::Select, MVT::v2i1, MVT::v2f64, 2},
+        {Instruction::Select, MVT::v4i1, MVT::v4f32, 2},
+        {Instruction::Select, MVT::v4i1, MVT::v4f16, 2},
+        {Instruction::Select, MVT::v8i1, MVT::v8f16, 2},
+        {Instruction::Select, MVT::v16i1, MVT::v16i16, 16},
+        {Instruction::Select, MVT::v8i1, MVT::v8i32, 8},
+        {Instruction::Select, MVT::v16i1, MVT::v16i32, 16},
+        {Instruction::Select, MVT::v4i1, MVT::v4i64, 4 * AmortizationCost},
+        {Instruction::Select, MVT::v8i1, MVT::v8i64, 8 * AmortizationCost},
+        {Instruction::Select, MVT::v16i1, MVT::v16i64, 16 * AmortizationCost}};
 
     EVT SelCondTy = TLI->getValueType(DL, CondTy);
     EVT SelValTy = TLI->getValueType(DL, ValTy);
     if (SelCondTy.isSimple() && SelValTy.isSimple()) {
-      if (const auto *Entry = ConvertCostTableLookup(VectorSelectTbl, ISD,
+      if (const auto *Entry = ConvertCostTableLookup(VectorSelectTbl, Opcode,
                                                      SelCondTy.getSimpleVT(),
                                                      SelValTy.getSimpleVT()))
         return Entry->Cost;
     }
   }
 
-  if (isa<FixedVectorType>(ValTy) && ISD == ISD::SETCC) {
-    Type *ValScalarTy = ValTy->getScalarType();
-    if ((ValScalarTy->isHalfTy() && !ST->hasFullFP16()) ||
-        ValScalarTy->isBFloatTy()) {
-      auto *ValVTy = cast<FixedVectorType>(ValTy);
-
-      // Without dedicated instructions we promote [b]f16 compares to f32.
-      auto *PromotedTy =
-          VectorType::get(Type::getFloatTy(ValTy->getContext()), ValVTy);
-
-      InstructionCost Cost = 0;
-      // Promote operands to float vectors.
-      Cost += 2 * getCastInstrCost(Instruction::FPExt, PromotedTy, ValTy,
-                                   TTI::CastContextHint::None, CostKind);
-      // Compare float vectors.
+  if (Opcode == Instruction::FCmp) {
+    // Without dedicated instructions we promote f16 + bf16 compares to f32.
+    if ((!ST->hasFullFP16() && ValTy->getScalarType()->isHalfTy()) ||
+        ValTy->getScalarType()->isBFloatTy()) {
+      Type *PromotedTy =
+          ValTy->getWithNewType(Type::getFloatTy(ValTy->getContext()));
+      InstructionCost Cost =
+          getCastInstrCost(Instruction::FPExt, PromotedTy, ValTy,
+                           TTI::CastContextHint::None, CostKind);
+      if (!Op1Info.isConstant() && !Op2Info.isConstant())
+        Cost *= 2;
       Cost += getCmpSelInstrCost(Opcode, PromotedTy, CondTy, VecPred, CostKind,
                                  Op1Info, Op2Info);
-      // During codegen we'll truncate the vector result from i32 to i16.
-      Cost +=
-          getCastInstrCost(Instruction::Trunc, VectorType::getInteger(ValVTy),
-                           VectorType::getInteger(PromotedTy),
-                           TTI::CastContextHint::None, CostKind);
+      if (ValTy->isVectorTy())
+        Cost += getCastInstrCost(
+            Instruction::Trunc, VectorType::getInteger(cast<VectorType>(ValTy)),
+            VectorType::getInteger(cast<VectorType>(PromotedTy)),
+            TTI::CastContextHint::None, CostKind);
       return Cost;
     }
+
+    auto LT = getTypeLegalizationCost(ValTy);
+    // Model unknown fp compares as a libcall.
+    if (LT.second.getScalarType() != MVT::f64 &&
+        LT.second.getScalarType() != MVT::f32 &&
+        LT.second.getScalarType() != MVT::f16)
+      return LT.first * getCallInstrCost(/*Function*/ nullptr, ValTy,
+                                         {ValTy, ValTy}, CostKind);
----------------
SamTebbs33 wrote:

Do we have to account for the complexity of the libcall itself as well, or is the call instruction cost enough?

https://github.com/llvm/llvm-project/pull/147940