SIFixSGPRCopies.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338
1//===-- SIFixSGPRCopies.cpp - Remove potential VGPR => SGPR copies --------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10/// \file 11/// Copies from VGPR to SGPR registers are illegal and the register coalescer 12/// will sometimes generate these illegal copies in situations like this: 13/// 14/// Register Class <vsrc> is the union of <vgpr> and <sgpr> 15/// 16/// BB0: 17/// %vreg0 <sgpr> = SCALAR_INST 18/// %vreg1 <vsrc> = COPY %vreg0 <sgpr> 19/// ... 20/// BRANCH %cond BB1, BB2 21/// BB1: 22/// %vreg2 <vgpr> = VECTOR_INST 23/// %vreg3 <vsrc> = COPY %vreg2 <vgpr> 24/// BB2: 25/// %vreg4 <vsrc> = PHI %vreg1 <vsrc>, <BB#0>, %vreg3 <vrsc>, <BB#1> 26/// %vreg5 <vgpr> = VECTOR_INST %vreg4 <vsrc> 27/// 28/// 29/// The coalescer will begin at BB0 and eliminate its copy, then the resulting 30/// code will look like this: 31/// 32/// BB0: 33/// %vreg0 <sgpr> = SCALAR_INST 34/// ... 35/// BRANCH %cond BB1, BB2 36/// BB1: 37/// %vreg2 <vgpr> = VECTOR_INST 38/// %vreg3 <vsrc> = COPY %vreg2 <vgpr> 39/// BB2: 40/// %vreg4 <sgpr> = PHI %vreg0 <sgpr>, <BB#0>, %vreg3 <vsrc>, <BB#1> 41/// %vreg5 <vgpr> = VECTOR_INST %vreg4 <sgpr> 42/// 43/// Now that the result of the PHI instruction is an SGPR, the register 44/// allocator is now forced to constrain the register class of %vreg3 to 45/// <sgpr> so we end up with final code like this: 46/// 47/// BB0: 48/// %vreg0 <sgpr> = SCALAR_INST 49/// ... 50/// BRANCH %cond BB1, BB2 51/// BB1: 52/// %vreg2 <vgpr> = VECTOR_INST 53/// %vreg3 <sgpr> = COPY %vreg2 <vgpr> 54/// BB2: 55/// %vreg4 <sgpr> = PHI %vreg0 <sgpr>, <BB#0>, %vreg3 <sgpr>, <BB#1> 56/// %vreg5 <vgpr> = VECTOR_INST %vreg4 <sgpr> 57/// 58/// Now this code contains an illegal copy from a VGPR to an SGPR. 59/// 60/// In order to avoid this problem, this pass searches for PHI instructions 61/// which define a <vsrc> register and constrains its definition class to 62/// <vgpr> if the user of the PHI's definition register is a vector instruction. 63/// If the PHI's definition class is constrained to <vgpr> then the coalescer 64/// will be unable to perform the COPY removal from the above example which 65/// ultimately led to the creation of an illegal COPY. 66//===----------------------------------------------------------------------===// 67 68#define DEBUG_TYPE "sgpr-copies" 69#include "AMDGPU.h" 70#include "SIInstrInfo.h" 71#include "llvm/CodeGen/MachineFunctionPass.h" 72#include "llvm/CodeGen/MachineInstrBuilder.h" 73#include "llvm/CodeGen/MachineRegisterInfo.h" 74#include "llvm/Support/Debug.h" 75#include "llvm/Support/raw_ostream.h" 76#include "llvm/Target/TargetMachine.h" 77 78using namespace llvm; 79 80namespace { 81 82class SIFixSGPRCopies : public MachineFunctionPass { 83 84private: 85 static char ID; 86 const TargetRegisterClass *inferRegClassFromUses(const SIRegisterInfo *TRI, 87 const MachineRegisterInfo &MRI, 88 unsigned Reg, 89 unsigned SubReg) const; 90 const TargetRegisterClass *inferRegClassFromDef(const SIRegisterInfo *TRI, 91 const MachineRegisterInfo &MRI, 92 unsigned Reg, 93 unsigned SubReg) const; 94 bool isVGPRToSGPRCopy(const MachineInstr &Copy, const SIRegisterInfo *TRI, 95 const MachineRegisterInfo &MRI) const; 96 97public: 98 SIFixSGPRCopies(TargetMachine &tm) : MachineFunctionPass(ID) { } 99 100 virtual bool runOnMachineFunction(MachineFunction &MF); 101 102 const char *getPassName() const { 103 return "SI Fix SGPR copies"; 104 } 105 106}; 107 108} // End anonymous namespace 109 110char SIFixSGPRCopies::ID = 0; 111 112FunctionPass *llvm::createSIFixSGPRCopiesPass(TargetMachine &tm) { 113 return new SIFixSGPRCopies(tm); 114} 115 116static bool hasVGPROperands(const MachineInstr &MI, const SIRegisterInfo *TRI) { 117 const MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo(); 118 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 119 if (!MI.getOperand(i).isReg() || 120 !TargetRegisterInfo::isVirtualRegister(MI.getOperand(i).getReg())) 121 continue; 122 123 if (TRI->hasVGPRs(MRI.getRegClass(MI.getOperand(i).getReg()))) 124 return true; 125 } 126 return false; 127} 128 129/// This functions walks the use list of Reg until it finds an Instruction 130/// that isn't a COPY returns the register class of that instruction. 131/// \return The register defined by the first non-COPY instruction. 132const TargetRegisterClass *SIFixSGPRCopies::inferRegClassFromUses( 133 const SIRegisterInfo *TRI, 134 const MachineRegisterInfo &MRI, 135 unsigned Reg, 136 unsigned SubReg) const { 137 // The Reg parameter to the function must always be defined by either a PHI 138 // or a COPY, therefore it cannot be a physical register. 139 assert(TargetRegisterInfo::isVirtualRegister(Reg) && 140 "Reg cannot be a physical register"); 141 142 const TargetRegisterClass *RC = MRI.getRegClass(Reg); 143 RC = TRI->getSubRegClass(RC, SubReg); 144 for (MachineRegisterInfo::use_instr_iterator 145 I = MRI.use_instr_begin(Reg), E = MRI.use_instr_end(); I != E; ++I) { 146 switch (I->getOpcode()) { 147 case AMDGPU::COPY: 148 RC = TRI->getCommonSubClass(RC, inferRegClassFromUses(TRI, MRI, 149 I->getOperand(0).getReg(), 150 I->getOperand(0).getSubReg())); 151 break; 152 } 153 } 154 155 return RC; 156} 157 158const TargetRegisterClass *SIFixSGPRCopies::inferRegClassFromDef( 159 const SIRegisterInfo *TRI, 160 const MachineRegisterInfo &MRI, 161 unsigned Reg, 162 unsigned SubReg) const { 163 if (!TargetRegisterInfo::isVirtualRegister(Reg)) { 164 const TargetRegisterClass *RC = TRI->getPhysRegClass(Reg); 165 return TRI->getSubRegClass(RC, SubReg); 166 } 167 MachineInstr *Def = MRI.getVRegDef(Reg); 168 if (Def->getOpcode() != AMDGPU::COPY) { 169 return TRI->getSubRegClass(MRI.getRegClass(Reg), SubReg); 170 } 171 172 return inferRegClassFromDef(TRI, MRI, Def->getOperand(1).getReg(), 173 Def->getOperand(1).getSubReg()); 174} 175 176bool SIFixSGPRCopies::isVGPRToSGPRCopy(const MachineInstr &Copy, 177 const SIRegisterInfo *TRI, 178 const MachineRegisterInfo &MRI) const { 179 180 unsigned DstReg = Copy.getOperand(0).getReg(); 181 unsigned SrcReg = Copy.getOperand(1).getReg(); 182 unsigned SrcSubReg = Copy.getOperand(1).getSubReg(); 183 const TargetRegisterClass *DstRC = MRI.getRegClass(DstReg); 184 const TargetRegisterClass *SrcRC; 185 186 if (!TargetRegisterInfo::isVirtualRegister(SrcReg) || 187 DstRC == &AMDGPU::M0RegRegClass) 188 return false; 189 190 SrcRC = TRI->getSubRegClass(MRI.getRegClass(SrcReg), SrcSubReg); 191 return TRI->isSGPRClass(DstRC) && TRI->hasVGPRs(SrcRC); 192} 193 194bool SIFixSGPRCopies::runOnMachineFunction(MachineFunction &MF) { 195 MachineRegisterInfo &MRI = MF.getRegInfo(); 196 const SIRegisterInfo *TRI = static_cast<const SIRegisterInfo *>( 197 MF.getTarget().getRegisterInfo()); 198 const SIInstrInfo *TII = static_cast<const SIInstrInfo *>( 199 MF.getTarget().getInstrInfo()); 200 for (MachineFunction::iterator BI = MF.begin(), BE = MF.end(); 201 BI != BE; ++BI) { 202 203 MachineBasicBlock &MBB = *BI; 204 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); 205 I != E; ++I) { 206 MachineInstr &MI = *I; 207 if (MI.getOpcode() == AMDGPU::COPY && isVGPRToSGPRCopy(MI, TRI, MRI)) { 208 DEBUG(dbgs() << "Fixing VGPR -> SGPR copy:\n"); 209 DEBUG(MI.print(dbgs())); 210 TII->moveToVALU(MI); 211 212 } 213 214 switch (MI.getOpcode()) { 215 default: continue; 216 case AMDGPU::PHI: { 217 DEBUG(dbgs() << " Fixing PHI:\n"); 218 DEBUG(MI.print(dbgs())); 219 220 for (unsigned i = 1; i < MI.getNumOperands(); i+=2) { 221 unsigned Reg = MI.getOperand(i).getReg(); 222 const TargetRegisterClass *RC = inferRegClassFromDef(TRI, MRI, Reg, 223 MI.getOperand(0).getSubReg()); 224 MRI.constrainRegClass(Reg, RC); 225 } 226 unsigned Reg = MI.getOperand(0).getReg(); 227 const TargetRegisterClass *RC = inferRegClassFromUses(TRI, MRI, Reg, 228 MI.getOperand(0).getSubReg()); 229 if (TRI->getCommonSubClass(RC, &AMDGPU::VReg_32RegClass)) { 230 MRI.constrainRegClass(Reg, &AMDGPU::VReg_32RegClass); 231 } 232 233 if (!TRI->isSGPRClass(MRI.getRegClass(Reg))) 234 break; 235 236 // If a PHI node defines an SGPR and any of its operands are VGPRs, 237 // then we need to move it to the VALU. 238 for (unsigned i = 1; i < MI.getNumOperands(); i+=2) { 239 unsigned Reg = MI.getOperand(i).getReg(); 240 if (TRI->hasVGPRs(MRI.getRegClass(Reg))) { 241 TII->moveToVALU(MI); 242 break; 243 } 244 } 245 246 break; 247 } 248 case AMDGPU::REG_SEQUENCE: { 249 if (TRI->hasVGPRs(TII->getOpRegClass(MI, 0)) || 250 !hasVGPROperands(MI, TRI)) 251 continue; 252 253 DEBUG(dbgs() << "Fixing REG_SEQUENCE:\n"); 254 DEBUG(MI.print(dbgs())); 255 256 TII->moveToVALU(MI); 257 break; 258 } 259 } 260 } 261 } 262 return false; 263} 264