[LLVM][CostModel][AArch64] Remove magic numbers from f16 vector compares. (#135795)

The PR also extends the code to cover bfloat vector compares that are
also promoted to float.

NOTE: There is a bail out for the compares that are scalarised that will
be removed by #135398.

Author: paulwalker-arm

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -4236,10 +4236,34 @@ InstructionCost AArch64TTIImpl::getCmpSelInstrCost(
   }
 
   if (isa<FixedVectorType>(ValTy) && ISD == ISD::SETCC) {
-    auto LT = getTypeLegalizationCost(ValTy);
-    // Cost v4f16 FCmp without FP16 support via converting to v4f32 and back.
-    if (LT.second == MVT::v4f16 && !ST->hasFullFP16())
-      return LT.first * 4; // fcvtl + fcvtl + fcmp + xtn
+    Type *ValScalarTy = ValTy->getScalarType();
+    if ((ValScalarTy->isHalfTy() && !ST->hasFullFP16()) ||
+        ValScalarTy->isBFloatTy()) {
+      auto *ValVTy = cast<FixedVectorType>(ValTy);
+
+      // FIXME: We currently scalarise these.
+      if (ValVTy->getNumElements() > 4)
+        return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy, VecPred,
+                                         CostKind, Op1Info, Op2Info, I);
+
+      // 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.
+      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);
+      return Cost;
+    }
   }
 
   // Treat the icmp in icmp(and, 0) as free, as we can make use of ands.

llvm/test/Analysis/CostModel/AArch64/vector-select.ll

@@ -168,7 +168,7 @@ define <2 x double> @v2f64_select_ogt(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_ogt(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_ogt'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp ogt <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp ogt <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -255,7 +255,7 @@ define <2 x double> @v2f64_select_oge(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_oge(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_oge'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp oge <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp oge <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -342,7 +342,7 @@ define <2 x double> @v2f64_select_olt(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_olt(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_olt'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp olt <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp olt <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -429,7 +429,7 @@ define <2 x double> @v2f64_select_ole(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_ole(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_ole'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp ole <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp ole <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -516,7 +516,7 @@ define <2 x double> @v2f64_select_oeq(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_oeq(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_oeq'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp oeq <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp oeq <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -603,7 +603,7 @@ define <2 x double> @v2f64_select_one(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_one(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_one'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp one <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp one <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -690,7 +690,7 @@ define <2 x double> @v2f64_select_une(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_une(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_une'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp une <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp une <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;
@@ -777,7 +777,7 @@ define <2 x double> @v2f64_select_ord(<2 x double> %a, <2 x double> %b, <2 x dou
 
 define <4 x bfloat> @v4bf16_select_ord(<4 x bfloat> %a, <4 x bfloat> %b, <4 x bfloat> %c) {
 ; COST-LABEL: 'v4bf16_select_ord'
-; COST-NEXT:  Cost Model: Found costs of 1 for: %cmp.1 = fcmp ord <4 x bfloat> %a, %b
+; COST-NEXT:  Cost Model: Found costs of RThru:4 CodeSize:1 Lat:1 SizeLat:1 for: %cmp.1 = fcmp ord <4 x bfloat> %a, %b
 ; COST-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:1 Lat:1 SizeLat:1 for: %s.1 = select <4 x i1> %cmp.1, <4 x bfloat> %a, <4 x bfloat> %c
 ; COST-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret <4 x bfloat> %s.1
 ;