[AArch64] Consider negated powers of 2 when calculating throughput cost

Negated powers of 2 have similar or (exact in the case of remainder) codegen with lowering sdiv. In the case of sdiv, it just negates the result in the end anyway, so nothing dissimilar at all.

Author: AZero13

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -4005,25 +4005,34 @@ InstructionCost AArch64TTIImpl::getArithmeticInstrCost(
       // have similar cost.
       auto VT = TLI->getValueType(DL, Ty);
       if (VT.isScalarInteger() && VT.getSizeInBits() <= 64) {
-        if (Op2Info.isPowerOf2()) {
+        if (Op2Info.isPowerOf2() || Op2Info.isNegatedPowerOf2()) {
+          // Neg can be folded into the asr instruction.
+          // FIXME: Is the throughput cost of asr + neg the same as just asr?
           return ISD == ISD::SDIV ? (3 * AddCost + AsrCost)
                                   : (3 * AsrCost + AddCost);
         } else {
           return MulCost + AsrCost + 2 * AddCost;
         }
       } else if (VT.isVector()) {
         InstructionCost UsraCost = 2 * AsrCost;
-        if (Op2Info.isPowerOf2()) {
+        if (Op2Info.isPowerOf2() || Op2Info.isNegatedPowerOf2()) {
           // Division with scalable types corresponds to native 'asrd'
           // instruction when SVE is available.
           // e.g. %1 = sdiv <vscale x 4 x i32> %a, splat (i32 8)
+
+          // One more for the negation in SDIV
+          InstructionCost cost =
+              (Op2Info.isNegatedPowerOf2() && ISD == ISD::SDIV) ? AsrCost : 0;
           if (Ty->isScalableTy() && ST->hasSVE())
-            return 2 * AsrCost;
-          return UsraCost +
-                 (ISD == ISD::SDIV
-                      ? (LT.second.getScalarType() == MVT::i64 ? 1 : 2) *
-                            AsrCost
-                      : 2 * AddCost);
+            cost += 2 * AsrCost;
+          else {
+            cost +=
+                UsraCost +
+                (ISD == ISD::SDIV
+                     ? (LT.second.getScalarType() == MVT::i64 ? 1 : 2) * AsrCost
+                     : 2 * AddCost);
+          }
+          return cost;
         } else if (LT.second == MVT::v2i64) {
           return VT.getVectorNumElements() *
                  getArithmeticInstrCost(Opcode, Ty->getScalarType(), CostKind,

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

@@ -870,27 +870,27 @@ define void @sdiv_uniformconstnegpow2() {
 ; CHECK-LABEL: 'sdiv_uniformconstnegpow2'
 ; CHECK-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:4 Lat:4 SizeLat:4 for: %I128 = sdiv i128 undef, -16
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I64 = sdiv i64 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V2i64 = sdiv <2 x i64> undef, splat (i64 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V4i64 = sdiv <4 x i64> undef, splat (i64 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:32 CodeSize:4 Lat:4 SizeLat:4 for: %V8i64 = sdiv <8 x i64> undef, splat (i64 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V2i64 = sdiv <2 x i64> undef, splat (i64 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V4i64 = sdiv <4 x i64> undef, splat (i64 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V8i64 = sdiv <8 x i64> undef, splat (i64 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I32 = sdiv i32 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V2i32 = sdiv <2 x i32> undef, splat (i32 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V4i32 = sdiv <4 x i32> undef, splat (i32 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:12 CodeSize:4 Lat:4 SizeLat:4 for: %V8i32 = sdiv <8 x i32> undef, splat (i32 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:24 CodeSize:4 Lat:4 SizeLat:4 for: %V16i32 = sdiv <16 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V2i32 = sdiv <2 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V4i32 = sdiv <4 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:4 Lat:4 SizeLat:4 for: %V8i32 = sdiv <8 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:20 CodeSize:4 Lat:4 SizeLat:4 for: %V16i32 = sdiv <16 x i32> undef, splat (i32 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I16 = sdiv i16 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V2i16 = sdiv <2 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V4i16 = sdiv <4 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V8i16 = sdiv <8 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:12 CodeSize:4 Lat:4 SizeLat:4 for: %V16i16 = sdiv <16 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:24 CodeSize:4 Lat:4 SizeLat:4 for: %V32i16 = sdiv <32 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V2i16 = sdiv <2 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V4i16 = sdiv <4 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V8i16 = sdiv <8 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:4 Lat:4 SizeLat:4 for: %V16i16 = sdiv <16 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:20 CodeSize:4 Lat:4 SizeLat:4 for: %V32i16 = sdiv <32 x i16> undef, splat (i16 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I8 = sdiv i8 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V2i8 = sdiv <2 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V4i8 = sdiv <4 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V8i8 = sdiv <8 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V16i8 = sdiv <16 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:12 CodeSize:4 Lat:4 SizeLat:4 for: %V32i8 = sdiv <32 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:24 CodeSize:4 Lat:4 SizeLat:4 for: %V64i8 = sdiv <64 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V2i8 = sdiv <2 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V4i8 = sdiv <4 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V8i8 = sdiv <8 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:5 CodeSize:4 Lat:4 SizeLat:4 for: %V16i8 = sdiv <16 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:4 Lat:4 SizeLat:4 for: %V32i8 = sdiv <32 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:20 CodeSize:4 Lat:4 SizeLat:4 for: %V64i8 = sdiv <64 x i8> undef, splat (i8 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret void
 ;
   %I128 = sdiv i128 undef, -16

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

@@ -870,27 +870,27 @@ define void @srem_uniformconstnegpow2() {
 ; CHECK-LABEL: 'srem_uniformconstnegpow2'
 ; CHECK-NEXT:  Cost Model: Found costs of RThru:10 CodeSize:4 Lat:4 SizeLat:4 for: %I128 = srem i128 undef, -16
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I64 = srem i64 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V2i64 = srem <2 x i64> undef, splat (i64 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V4i64 = srem <4 x i64> undef, splat (i64 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:32 CodeSize:4 Lat:4 SizeLat:4 for: %V8i64 = srem <8 x i64> undef, splat (i64 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V2i64 = srem <2 x i64> undef, splat (i64 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V4i64 = srem <4 x i64> undef, splat (i64 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V8i64 = srem <8 x i64> undef, splat (i64 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I32 = srem i32 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V2i32 = srem <2 x i32> undef, splat (i32 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V4i32 = srem <4 x i32> undef, splat (i32 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:12 CodeSize:4 Lat:4 SizeLat:4 for: %V8i32 = srem <8 x i32> undef, splat (i32 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:24 CodeSize:4 Lat:4 SizeLat:4 for: %V16i32 = srem <16 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V2i32 = srem <2 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V4i32 = srem <4 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V8i32 = srem <8 x i32> undef, splat (i32 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V16i32 = srem <16 x i32> undef, splat (i32 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I16 = srem i16 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V2i16 = srem <2 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V4i16 = srem <4 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V8i16 = srem <8 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:12 CodeSize:4 Lat:4 SizeLat:4 for: %V16i16 = srem <16 x i16> undef, splat (i16 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:24 CodeSize:4 Lat:4 SizeLat:4 for: %V32i16 = srem <32 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V2i16 = srem <2 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V4i16 = srem <4 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V8i16 = srem <8 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V16i16 = srem <16 x i16> undef, splat (i16 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V32i16 = srem <32 x i16> undef, splat (i16 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of 4 for: %I8 = srem i8 undef, -16
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V2i8 = srem <2 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V4i8 = srem <4 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V8i8 = srem <8 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:6 CodeSize:4 Lat:4 SizeLat:4 for: %V16i8 = srem <16 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:12 CodeSize:4 Lat:4 SizeLat:4 for: %V32i8 = srem <32 x i8> undef, splat (i8 -16)
-; CHECK-NEXT:  Cost Model: Found costs of RThru:24 CodeSize:4 Lat:4 SizeLat:4 for: %V64i8 = srem <64 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V2i8 = srem <2 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V4i8 = srem <4 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V8i8 = srem <8 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of 4 for: %V16i8 = srem <16 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:8 CodeSize:4 Lat:4 SizeLat:4 for: %V32i8 = srem <32 x i8> undef, splat (i8 -16)
+; CHECK-NEXT:  Cost Model: Found costs of RThru:16 CodeSize:4 Lat:4 SizeLat:4 for: %V64i8 = srem <64 x i8> undef, splat (i8 -16)
 ; CHECK-NEXT:  Cost Model: Found costs of RThru:0 CodeSize:1 Lat:1 SizeLat:1 for: ret void
 ;
   %I128 = srem i128 undef, -16