1 //===- X86CompressEVEX.cpp ------------------------------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass compresses instructions from EVEX space to legacy/VEX/EVEX space 10 // when possible in order to reduce code size or facilitate HW decoding. 11 // 12 // Possible compression: 13 // a. AVX512 instruction (EVEX) -> AVX instruction (VEX) 14 // b. Promoted instruction (EVEX) -> pre-promotion instruction (legacy/VEX) 15 // c. NDD (EVEX) -> non-NDD (legacy) 16 // d. NF_ND (EVEX) -> NF (EVEX) 17 // 18 // Compression a, b and c can always reduce code size, with some exceptions 19 // such as promoted 16-bit CRC32 which is as long as the legacy version. 20 // 21 // legacy: 22 // crc32w %si, %eax ## encoding: [0x66,0xf2,0x0f,0x38,0xf1,0xc6] 23 // promoted: 24 // crc32w %si, %eax ## encoding: [0x62,0xf4,0x7d,0x08,0xf1,0xc6] 25 // 26 // From performance perspective, these should be same (same uops and same EXE 27 // ports). From a FMV perspective, an older legacy encoding is preferred b/c it 28 // can execute in more places (broader HW install base). So we will still do 29 // the compression. 30 // 31 // Compression d can help hardware decode (HW may skip reading the NDD 32 // register) although the instruction length remains unchanged. 33 //===----------------------------------------------------------------------===// 34 35 #include "MCTargetDesc/X86BaseInfo.h" 36 #include "MCTargetDesc/X86InstComments.h" 37 #include "X86.h" 38 #include "X86InstrInfo.h" 39 #include "X86Subtarget.h" 40 #include "llvm/ADT/StringRef.h" 41 #include "llvm/CodeGen/MachineFunction.h" 42 #include "llvm/CodeGen/MachineFunctionPass.h" 43 #include "llvm/CodeGen/MachineInstr.h" 44 #include "llvm/CodeGen/MachineOperand.h" 45 #include "llvm/MC/MCInstrDesc.h" 46 #include "llvm/Pass.h" 47 #include <atomic> 48 #include <cassert> 49 #include <cstdint> 50 51 using namespace llvm; 52 53 // Including the generated EVEX compression tables. 54 struct X86CompressEVEXTableEntry { 55 uint16_t OldOpc; 56 uint16_t NewOpc; 57 58 bool operator<(const X86CompressEVEXTableEntry &RHS) const { 59 return OldOpc < RHS.OldOpc; 60 } 61 62 friend bool operator<(const X86CompressEVEXTableEntry &TE, unsigned Opc) { 63 return TE.OldOpc < Opc; 64 } 65 }; 66 #include "X86GenCompressEVEXTables.inc" 67 68 #define COMP_EVEX_DESC "Compressing EVEX instrs when possible" 69 #define COMP_EVEX_NAME "x86-compress-evex" 70 71 #define DEBUG_TYPE COMP_EVEX_NAME 72 73 namespace { 74 75 class CompressEVEXPass : public MachineFunctionPass { 76 public: 77 static char ID; 78 CompressEVEXPass() : MachineFunctionPass(ID) {} 79 StringRef getPassName() const override { return COMP_EVEX_DESC; } 80 81 bool runOnMachineFunction(MachineFunction &MF) override; 82 83 // This pass runs after regalloc and doesn't support VReg operands. 84 MachineFunctionProperties getRequiredProperties() const override { 85 return MachineFunctionProperties().set( 86 MachineFunctionProperties::Property::NoVRegs); 87 } 88 }; 89 90 } // end anonymous namespace 91 92 char CompressEVEXPass::ID = 0; 93 94 static bool usesExtendedRegister(const MachineInstr &MI) { 95 auto isHiRegIdx = [](unsigned Reg) { 96 // Check for XMM register with indexes between 16 - 31. 97 if (Reg >= X86::XMM16 && Reg <= X86::XMM31) 98 return true; 99 // Check for YMM register with indexes between 16 - 31. 100 if (Reg >= X86::YMM16 && Reg <= X86::YMM31) 101 return true; 102 // Check for GPR with indexes between 16 - 31. 103 if (X86II::isApxExtendedReg(Reg)) 104 return true; 105 return false; 106 }; 107 108 // Check that operands are not ZMM regs or 109 // XMM/YMM regs with hi indexes between 16 - 31. 110 for (const MachineOperand &MO : MI.explicit_operands()) { 111 if (!MO.isReg()) 112 continue; 113 114 Register Reg = MO.getReg(); 115 assert(!X86II::isZMMReg(Reg) && 116 "ZMM instructions should not be in the EVEX->VEX tables"); 117 if (isHiRegIdx(Reg)) 118 return true; 119 } 120 121 return false; 122 } 123 124 static bool checkVEXInstPredicate(unsigned OldOpc, const X86Subtarget &ST) { 125 switch (OldOpc) { 126 default: 127 return true; 128 case X86::VCVTNEPS2BF16Z128rm: 129 case X86::VCVTNEPS2BF16Z128rr: 130 case X86::VCVTNEPS2BF16Z256rm: 131 case X86::VCVTNEPS2BF16Z256rr: 132 return ST.hasAVXNECONVERT(); 133 case X86::VPDPBUSDSZ128m: 134 case X86::VPDPBUSDSZ128r: 135 case X86::VPDPBUSDSZ256m: 136 case X86::VPDPBUSDSZ256r: 137 case X86::VPDPBUSDZ128m: 138 case X86::VPDPBUSDZ128r: 139 case X86::VPDPBUSDZ256m: 140 case X86::VPDPBUSDZ256r: 141 case X86::VPDPWSSDSZ128m: 142 case X86::VPDPWSSDSZ128r: 143 case X86::VPDPWSSDSZ256m: 144 case X86::VPDPWSSDSZ256r: 145 case X86::VPDPWSSDZ128m: 146 case X86::VPDPWSSDZ128r: 147 case X86::VPDPWSSDZ256m: 148 case X86::VPDPWSSDZ256r: 149 return ST.hasAVXVNNI(); 150 case X86::VPMADD52HUQZ128m: 151 case X86::VPMADD52HUQZ128r: 152 case X86::VPMADD52HUQZ256m: 153 case X86::VPMADD52HUQZ256r: 154 case X86::VPMADD52LUQZ128m: 155 case X86::VPMADD52LUQZ128r: 156 case X86::VPMADD52LUQZ256m: 157 case X86::VPMADD52LUQZ256r: 158 return ST.hasAVXIFMA(); 159 } 160 } 161 162 // Do any custom cleanup needed to finalize the conversion. 163 static bool performCustomAdjustments(MachineInstr &MI, unsigned NewOpc) { 164 (void)NewOpc; 165 unsigned Opc = MI.getOpcode(); 166 switch (Opc) { 167 case X86::VALIGNDZ128rri: 168 case X86::VALIGNDZ128rmi: 169 case X86::VALIGNQZ128rri: 170 case X86::VALIGNQZ128rmi: { 171 assert((NewOpc == X86::VPALIGNRrri || NewOpc == X86::VPALIGNRrmi) && 172 "Unexpected new opcode!"); 173 unsigned Scale = 174 (Opc == X86::VALIGNQZ128rri || Opc == X86::VALIGNQZ128rmi) ? 8 : 4; 175 MachineOperand &Imm = MI.getOperand(MI.getNumExplicitOperands() - 1); 176 Imm.setImm(Imm.getImm() * Scale); 177 break; 178 } 179 case X86::VSHUFF32X4Z256rmi: 180 case X86::VSHUFF32X4Z256rri: 181 case X86::VSHUFF64X2Z256rmi: 182 case X86::VSHUFF64X2Z256rri: 183 case X86::VSHUFI32X4Z256rmi: 184 case X86::VSHUFI32X4Z256rri: 185 case X86::VSHUFI64X2Z256rmi: 186 case X86::VSHUFI64X2Z256rri: { 187 assert((NewOpc == X86::VPERM2F128rr || NewOpc == X86::VPERM2I128rr || 188 NewOpc == X86::VPERM2F128rm || NewOpc == X86::VPERM2I128rm) && 189 "Unexpected new opcode!"); 190 MachineOperand &Imm = MI.getOperand(MI.getNumExplicitOperands() - 1); 191 int64_t ImmVal = Imm.getImm(); 192 // Set bit 5, move bit 1 to bit 4, copy bit 0. 193 Imm.setImm(0x20 | ((ImmVal & 2) << 3) | (ImmVal & 1)); 194 break; 195 } 196 case X86::VRNDSCALEPDZ128rri: 197 case X86::VRNDSCALEPDZ128rmi: 198 case X86::VRNDSCALEPSZ128rri: 199 case X86::VRNDSCALEPSZ128rmi: 200 case X86::VRNDSCALEPDZ256rri: 201 case X86::VRNDSCALEPDZ256rmi: 202 case X86::VRNDSCALEPSZ256rri: 203 case X86::VRNDSCALEPSZ256rmi: 204 case X86::VRNDSCALESDZr: 205 case X86::VRNDSCALESDZm: 206 case X86::VRNDSCALESSZr: 207 case X86::VRNDSCALESSZm: 208 case X86::VRNDSCALESDZr_Int: 209 case X86::VRNDSCALESDZm_Int: 210 case X86::VRNDSCALESSZr_Int: 211 case X86::VRNDSCALESSZm_Int: 212 const MachineOperand &Imm = MI.getOperand(MI.getNumExplicitOperands() - 1); 213 int64_t ImmVal = Imm.getImm(); 214 // Ensure that only bits 3:0 of the immediate are used. 215 if ((ImmVal & 0xf) != ImmVal) 216 return false; 217 break; 218 } 219 220 return true; 221 } 222 223 static bool CompressEVEXImpl(MachineInstr &MI, const X86Subtarget &ST) { 224 uint64_t TSFlags = MI.getDesc().TSFlags; 225 226 // Check for EVEX instructions only. 227 if ((TSFlags & X86II::EncodingMask) != X86II::EVEX) 228 return false; 229 230 // Instructions with mask or 512-bit vector can't be converted to VEX. 231 if (TSFlags & (X86II::EVEX_K | X86II::EVEX_L2)) 232 return false; 233 234 // EVEX_B has several meanings. 235 // AVX512: 236 // register form: rounding control or SAE 237 // memory form: broadcast 238 // 239 // APX: 240 // MAP4: NDD 241 // 242 // For AVX512 cases, EVEX prefix is needed in order to carry this information 243 // thus preventing the transformation to VEX encoding. 244 if (TSFlags & X86II::EVEX_B) 245 return false; 246 247 ArrayRef<X86CompressEVEXTableEntry> Table = ArrayRef(X86CompressEVEXTable); 248 249 unsigned Opc = MI.getOpcode(); 250 const auto *I = llvm::lower_bound(Table, Opc); 251 if (I == Table.end() || I->OldOpc != Opc) 252 return false; 253 254 if (usesExtendedRegister(MI) || !checkVEXInstPredicate(Opc, ST) || 255 !performCustomAdjustments(MI, I->NewOpc)) 256 return false; 257 258 const MCInstrDesc &NewDesc = ST.getInstrInfo()->get(I->NewOpc); 259 MI.setDesc(NewDesc); 260 uint64_t Encoding = NewDesc.TSFlags & X86II::EncodingMask; 261 auto AsmComment = 262 (Encoding == X86II::VEX) ? X86::AC_EVEX_2_VEX : X86::AC_EVEX_2_LEGACY; 263 MI.setAsmPrinterFlag(AsmComment); 264 return true; 265 } 266 267 bool CompressEVEXPass::runOnMachineFunction(MachineFunction &MF) { 268 #ifndef NDEBUG 269 // Make sure the tables are sorted. 270 static std::atomic<bool> TableChecked(false); 271 if (!TableChecked.load(std::memory_order_relaxed)) { 272 assert(llvm::is_sorted(X86CompressEVEXTable) && 273 "X86CompressEVEXTable is not sorted!"); 274 TableChecked.store(true, std::memory_order_relaxed); 275 } 276 #endif 277 const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>(); 278 if (!ST.hasAVX512() && !ST.hasEGPR() && !ST.hasNDD()) 279 return false; 280 281 bool Changed = false; 282 283 for (MachineBasicBlock &MBB : MF) { 284 // Traverse the basic block. 285 for (MachineInstr &MI : MBB) 286 Changed |= CompressEVEXImpl(MI, ST); 287 } 288 289 return Changed; 290 } 291 292 INITIALIZE_PASS(CompressEVEXPass, COMP_EVEX_NAME, COMP_EVEX_DESC, false, false) 293 294 FunctionPass *llvm::createX86CompressEVEXPass() { 295 return new CompressEVEXPass(); 296 } 297