[CostModel][X86] Update BITREVERSE costs for GFNI targets

Inspired by the recent patches by @shamithoke - we have real scheduler model numbers for GFNI instructions now, allowing us to calculate an upper bounds costs table instead of performing it analytically.

Author: RKSimon

llvm/lib/Target/X86/X86TargetTransformInfo.cpp

@@ -3820,6 +3820,24 @@ X86TTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     { ISD::FSQRT,      MVT::v2f64,   { 27, 27,  1,  1 } }, // vsqrtpd
     { ISD::FSQRT,      MVT::v4f64,   { 54, 54,  1,  3 } }, // vsqrtpd
   };
+  static const CostKindTblEntry GFNICostTbl[] = {
+    { ISD::BITREVERSE, MVT::i8,      {  3,  3,  3,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::i16,     {  3,  3,  4,  6 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::i32,     {  3,  3,  4,  5 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::i64,     {  3,  3,  4,  6 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v16i8,   {  1,  6,  1,  2 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v32i8,   {  1,  6,  1,  2 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v64i8,   {  1,  6,  1,  2 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v8i16,   {  1,  8,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v16i16,  {  1,  9,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v32i16,  {  1,  9,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v4i32,   {  1,  8,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v8i32,   {  1,  9,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v16i32,  {  1,  9,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v2i64,   {  1,  8,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v4i64,   {  1,  9,  2,  4 } }, // gf2p8affineqb
+    { ISD::BITREVERSE, MVT::v8i64,   {  1,  9,  2,  4 } }, // gf2p8affineqb
+  };
   static const CostKindTblEntry GLMCostTbl[] = {
     { ISD::FSQRT,      MVT::f32,     { 19, 20, 1, 1 } }, // sqrtss
     { ISD::FSQRT,      MVT::v4f32,   { 37, 41, 1, 5 } }, // sqrtps
@@ -4156,23 +4174,6 @@ X86TTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(OpTy);
     MVT MTy = LT.second;
 
-    // Attempt to lookup cost.
-    if (ISD == ISD::BITREVERSE && ST->hasGFNI() && ST->hasSSSE3() &&
-        MTy.isVector()) {
-      // With PSHUFB the code is very similar for all types. If we have integer
-      // byte operations, we just need a GF2P8AFFINEQB for vXi8. For other types
-      // we also need a PSHUFB.
-      unsigned Cost = MTy.getVectorElementType() == MVT::i8 ? 1 : 2;
-
-      // Without byte operations, we need twice as many GF2P8AFFINEQB and PSHUFB
-      // instructions. We also need an extract and an insert.
-      if (!(MTy.is128BitVector() || (ST->hasAVX2() && MTy.is256BitVector()) ||
-            (ST->hasBWI() && MTy.is512BitVector())))
-        Cost = Cost * 2 + 2;
-
-      return LT.first * Cost;
-    }
-
     // Without BMI/LZCNT see if we're only looking for a *_ZERO_UNDEF cost.
     if (((ISD == ISD::CTTZ && !ST->hasBMI()) ||
          (ISD == ISD::CTLZ && !ST->hasLZCNT())) &&
@@ -4230,6 +4231,12 @@ X86TTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
           return adjustTableCost(Entry->ISD, *KindCost, LT.first,
                                  ICA.getFlags());
 
+    if (ST->hasGFNI())
+      if (const auto *Entry = CostTableLookup(GFNICostTbl, ISD, MTy))
+        if (auto KindCost = Entry->Cost[CostKind])
+          return adjustTableCost(Entry->ISD, *KindCost, LT.first,
+                                 ICA.getFlags());
+
     if (ST->hasCDI())
       if (const auto *Entry = CostTableLookup(AVX512CDCostTbl, ISD, MTy))
         if (auto KindCost = Entry->Cost[CostKind])