1 //===-- SILowerControlFlow.cpp - Use predicates for control flow ----------===// 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 /// \brief This pass lowers the pseudo control flow instructions to real 12 /// machine instructions. 13 /// 14 /// All control flow is handled using predicated instructions and 15 /// a predicate stack. Each Scalar ALU controls the operations of 64 Vector 16 /// ALUs. The Scalar ALU can update the predicate for any of the Vector ALUs 17 /// by writting to the 64-bit EXEC register (each bit corresponds to a 18 /// single vector ALU). Typically, for predicates, a vector ALU will write 19 /// to its bit of the VCC register (like EXEC VCC is 64-bits, one for each 20 /// Vector ALU) and then the ScalarALU will AND the VCC register with the 21 /// EXEC to update the predicates. 22 /// 23 /// For example: 24 /// %VCC = V_CMP_GT_F32 %VGPR1, %VGPR2 25 /// %SGPR0 = SI_IF %VCC 26 /// %VGPR0 = V_ADD_F32 %VGPR0, %VGPR0 27 /// %SGPR0 = SI_ELSE %SGPR0 28 /// %VGPR0 = V_SUB_F32 %VGPR0, %VGPR0 29 /// SI_END_CF %SGPR0 30 /// 31 /// becomes: 32 /// 33 /// %SGPR0 = S_AND_SAVEEXEC_B64 %VCC // Save and update the exec mask 34 /// %SGPR0 = S_XOR_B64 %SGPR0, %EXEC // Clear live bits from saved exec mask 35 /// S_CBRANCH_EXECZ label0 // This instruction is an optional 36 /// // optimization which allows us to 37 /// // branch if all the bits of 38 /// // EXEC are zero. 39 /// %VGPR0 = V_ADD_F32 %VGPR0, %VGPR0 // Do the IF block of the branch 40 /// 41 /// label0: 42 /// %SGPR0 = S_OR_SAVEEXEC_B64 %EXEC // Restore the exec mask for the Then block 43 /// %EXEC = S_XOR_B64 %SGPR0, %EXEC // Clear live bits from saved exec mask 44 /// S_BRANCH_EXECZ label1 // Use our branch optimization 45 /// // instruction again. 46 /// %VGPR0 = V_SUB_F32 %VGPR0, %VGPR // Do the THEN block 47 /// label1: 48 /// %EXEC = S_OR_B64 %EXEC, %SGPR0 // Re-enable saved exec mask bits 49 //===----------------------------------------------------------------------===// 50 51 #include "AMDGPU.h" 52 #include "SIInstrInfo.h" 53 #include "SIMachineFunctionInfo.h" 54 #include "llvm/CodeGen/MachineFunction.h" 55 #include "llvm/CodeGen/MachineFunctionPass.h" 56 #include "llvm/CodeGen/MachineInstrBuilder.h" 57 #include "llvm/CodeGen/MachineRegisterInfo.h" 58 59 using namespace llvm; 60 61 namespace { 62 63 class SILowerControlFlowPass : public MachineFunctionPass { 64 65 private: 66 static const unsigned SkipThreshold = 12; 67 68 static char ID; 69 const TargetRegisterInfo *TRI; 70 const TargetInstrInfo *TII; 71 72 bool shouldSkip(MachineBasicBlock *From, MachineBasicBlock *To); 73 74 void Skip(MachineInstr &From, MachineOperand &To); 75 void SkipIfDead(MachineInstr &MI); 76 77 void If(MachineInstr &MI); 78 void Else(MachineInstr &MI); 79 void Break(MachineInstr &MI); 80 void IfBreak(MachineInstr &MI); 81 void ElseBreak(MachineInstr &MI); 82 void Loop(MachineInstr &MI); 83 void EndCf(MachineInstr &MI); 84 85 void Kill(MachineInstr &MI); 86 void Branch(MachineInstr &MI); 87 88 void LoadM0(MachineInstr &MI, MachineInstr *MovRel); 89 void IndirectSrc(MachineInstr &MI); 90 void IndirectDst(MachineInstr &MI); 91 92 public: 93 SILowerControlFlowPass(TargetMachine &tm) : 94 MachineFunctionPass(ID), TRI(tm.getRegisterInfo()), 95 TII(tm.getInstrInfo()) { } 96 97 virtual bool runOnMachineFunction(MachineFunction &MF); 98 99 const char *getPassName() const { 100 return "SI Lower control flow instructions"; 101 } 102 103 }; 104 105 } // End anonymous namespace 106 107 char SILowerControlFlowPass::ID = 0; 108 109 FunctionPass *llvm::createSILowerControlFlowPass(TargetMachine &tm) { 110 return new SILowerControlFlowPass(tm); 111 } 112 113 bool SILowerControlFlowPass::shouldSkip(MachineBasicBlock *From, 114 MachineBasicBlock *To) { 115 116 unsigned NumInstr = 0; 117 118 for (MachineBasicBlock *MBB = From; MBB != To && !MBB->succ_empty(); 119 MBB = *MBB->succ_begin()) { 120 121 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); 122 NumInstr < SkipThreshold && I != E; ++I) { 123 124 if (I->isBundle() || !I->isBundled()) 125 if (++NumInstr >= SkipThreshold) 126 return true; 127 } 128 } 129 130 return false; 131 } 132 133 void SILowerControlFlowPass::Skip(MachineInstr &From, MachineOperand &To) { 134 135 if (!shouldSkip(*From.getParent()->succ_begin(), To.getMBB())) 136 return; 137 138 DebugLoc DL = From.getDebugLoc(); 139 BuildMI(*From.getParent(), &From, DL, TII->get(AMDGPU::S_CBRANCH_EXECZ)) 140 .addOperand(To) 141 .addReg(AMDGPU::EXEC); 142 } 143 144 void SILowerControlFlowPass::SkipIfDead(MachineInstr &MI) { 145 146 MachineBasicBlock &MBB = *MI.getParent(); 147 DebugLoc DL = MI.getDebugLoc(); 148 149 if (!shouldSkip(&MBB, &MBB.getParent()->back())) 150 return; 151 152 MachineBasicBlock::iterator Insert = &MI; 153 ++Insert; 154 155 // If the exec mask is non-zero, skip the next two instructions 156 BuildMI(MBB, Insert, DL, TII->get(AMDGPU::S_CBRANCH_EXECNZ)) 157 .addImm(3) 158 .addReg(AMDGPU::EXEC); 159 160 // Exec mask is zero: Export to NULL target... 161 BuildMI(MBB, Insert, DL, TII->get(AMDGPU::EXP)) 162 .addImm(0) 163 .addImm(0x09) // V_008DFC_SQ_EXP_NULL 164 .addImm(0) 165 .addImm(1) 166 .addImm(1) 167 .addReg(AMDGPU::VGPR0) 168 .addReg(AMDGPU::VGPR0) 169 .addReg(AMDGPU::VGPR0) 170 .addReg(AMDGPU::VGPR0); 171 172 // ... and terminate wavefront 173 BuildMI(MBB, Insert, DL, TII->get(AMDGPU::S_ENDPGM)); 174 } 175 176 void SILowerControlFlowPass::If(MachineInstr &MI) { 177 MachineBasicBlock &MBB = *MI.getParent(); 178 DebugLoc DL = MI.getDebugLoc(); 179 unsigned Reg = MI.getOperand(0).getReg(); 180 unsigned Vcc = MI.getOperand(1).getReg(); 181 182 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_AND_SAVEEXEC_B64), Reg) 183 .addReg(Vcc); 184 185 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_XOR_B64), Reg) 186 .addReg(AMDGPU::EXEC) 187 .addReg(Reg); 188 189 Skip(MI, MI.getOperand(2)); 190 191 MI.eraseFromParent(); 192 } 193 194 void SILowerControlFlowPass::Else(MachineInstr &MI) { 195 MachineBasicBlock &MBB = *MI.getParent(); 196 DebugLoc DL = MI.getDebugLoc(); 197 unsigned Dst = MI.getOperand(0).getReg(); 198 unsigned Src = MI.getOperand(1).getReg(); 199 200 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_SAVEEXEC_B64), Dst) 201 .addReg(Src); // Saved EXEC 202 203 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_XOR_B64), AMDGPU::EXEC) 204 .addReg(AMDGPU::EXEC) 205 .addReg(Dst); 206 207 Skip(MI, MI.getOperand(2)); 208 209 MI.eraseFromParent(); 210 } 211 212 void SILowerControlFlowPass::Break(MachineInstr &MI) { 213 MachineBasicBlock &MBB = *MI.getParent(); 214 DebugLoc DL = MI.getDebugLoc(); 215 216 unsigned Dst = MI.getOperand(0).getReg(); 217 unsigned Src = MI.getOperand(1).getReg(); 218 219 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst) 220 .addReg(AMDGPU::EXEC) 221 .addReg(Src); 222 223 MI.eraseFromParent(); 224 } 225 226 void SILowerControlFlowPass::IfBreak(MachineInstr &MI) { 227 MachineBasicBlock &MBB = *MI.getParent(); 228 DebugLoc DL = MI.getDebugLoc(); 229 230 unsigned Dst = MI.getOperand(0).getReg(); 231 unsigned Vcc = MI.getOperand(1).getReg(); 232 unsigned Src = MI.getOperand(2).getReg(); 233 234 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst) 235 .addReg(Vcc) 236 .addReg(Src); 237 238 MI.eraseFromParent(); 239 } 240 241 void SILowerControlFlowPass::ElseBreak(MachineInstr &MI) { 242 MachineBasicBlock &MBB = *MI.getParent(); 243 DebugLoc DL = MI.getDebugLoc(); 244 245 unsigned Dst = MI.getOperand(0).getReg(); 246 unsigned Saved = MI.getOperand(1).getReg(); 247 unsigned Src = MI.getOperand(2).getReg(); 248 249 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst) 250 .addReg(Saved) 251 .addReg(Src); 252 253 MI.eraseFromParent(); 254 } 255 256 void SILowerControlFlowPass::Loop(MachineInstr &MI) { 257 MachineBasicBlock &MBB = *MI.getParent(); 258 DebugLoc DL = MI.getDebugLoc(); 259 unsigned Src = MI.getOperand(0).getReg(); 260 261 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_ANDN2_B64), AMDGPU::EXEC) 262 .addReg(AMDGPU::EXEC) 263 .addReg(Src); 264 265 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_CBRANCH_EXECNZ)) 266 .addOperand(MI.getOperand(1)) 267 .addReg(AMDGPU::EXEC); 268 269 MI.eraseFromParent(); 270 } 271 272 void SILowerControlFlowPass::EndCf(MachineInstr &MI) { 273 MachineBasicBlock &MBB = *MI.getParent(); 274 DebugLoc DL = MI.getDebugLoc(); 275 unsigned Reg = MI.getOperand(0).getReg(); 276 277 BuildMI(MBB, MBB.getFirstNonPHI(), DL, 278 TII->get(AMDGPU::S_OR_B64), AMDGPU::EXEC) 279 .addReg(AMDGPU::EXEC) 280 .addReg(Reg); 281 282 MI.eraseFromParent(); 283 } 284 285 void SILowerControlFlowPass::Branch(MachineInstr &MI) { 286 MachineBasicBlock *Next = MI.getParent()->getNextNode(); 287 MachineBasicBlock *Target = MI.getOperand(0).getMBB(); 288 if (Target == Next) 289 MI.eraseFromParent(); 290 else 291 assert(0); 292 } 293 294 void SILowerControlFlowPass::Kill(MachineInstr &MI) { 295 296 MachineBasicBlock &MBB = *MI.getParent(); 297 DebugLoc DL = MI.getDebugLoc(); 298 299 // Kill is only allowed in pixel shaders 300 assert(MBB.getParent()->getInfo<SIMachineFunctionInfo>()->ShaderType == 301 ShaderType::PIXEL); 302 303 // Clear this pixel from the exec mask if the operand is negative 304 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_CMPX_LE_F32_e32), AMDGPU::VCC) 305 .addImm(0) 306 .addOperand(MI.getOperand(0)); 307 308 MI.eraseFromParent(); 309 } 310 311 void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel) { 312 313 MachineBasicBlock &MBB = *MI.getParent(); 314 DebugLoc DL = MI.getDebugLoc(); 315 MachineBasicBlock::iterator I = MI; 316 317 unsigned Save = MI.getOperand(1).getReg(); 318 unsigned Idx = MI.getOperand(3).getReg(); 319 320 if (AMDGPU::SReg_32RegClass.contains(Idx)) { 321 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0) 322 .addReg(Idx); 323 MBB.insert(I, MovRel); 324 MI.eraseFromParent(); 325 return; 326 } 327 328 assert(AMDGPU::SReg_64RegClass.contains(Save)); 329 assert(AMDGPU::VReg_32RegClass.contains(Idx)); 330 331 // Save the EXEC mask 332 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B64), Save) 333 .addReg(AMDGPU::EXEC); 334 335 // Read the next variant into VCC (lower 32 bits) <- also loop target 336 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_READFIRSTLANE_B32_e32), AMDGPU::VCC) 337 .addReg(Idx); 338 339 // Move index from VCC into M0 340 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0) 341 .addReg(AMDGPU::VCC); 342 343 // Compare the just read M0 value to all possible Idx values 344 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_CMP_EQ_U32_e32), AMDGPU::VCC) 345 .addReg(AMDGPU::M0) 346 .addReg(Idx); 347 348 // Update EXEC, save the original EXEC value to VCC 349 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_AND_SAVEEXEC_B64), AMDGPU::VCC) 350 .addReg(AMDGPU::VCC); 351 352 // Do the actual move 353 MBB.insert(I, MovRel); 354 355 // Update EXEC, switch all done bits to 0 and all todo bits to 1 356 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_XOR_B64), AMDGPU::EXEC) 357 .addReg(AMDGPU::EXEC) 358 .addReg(AMDGPU::VCC); 359 360 // Loop back to V_READFIRSTLANE_B32 if there are still variants to cover 361 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_CBRANCH_EXECNZ)) 362 .addImm(-7) 363 .addReg(AMDGPU::EXEC); 364 365 // Restore EXEC 366 BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B64), AMDGPU::EXEC) 367 .addReg(Save); 368 369 MI.eraseFromParent(); 370 } 371 372 void SILowerControlFlowPass::IndirectSrc(MachineInstr &MI) { 373 374 MachineBasicBlock &MBB = *MI.getParent(); 375 DebugLoc DL = MI.getDebugLoc(); 376 377 unsigned Dst = MI.getOperand(0).getReg(); 378 unsigned Vec = MI.getOperand(2).getReg(); 379 unsigned Off = MI.getOperand(4).getImm(); 380 381 MachineInstr *MovRel = 382 BuildMI(*MBB.getParent(), DL, TII->get(AMDGPU::V_MOVRELS_B32_e32), Dst) 383 .addReg(TRI->getSubReg(Vec, AMDGPU::sub0) + Off) 384 .addReg(AMDGPU::M0, RegState::Implicit) 385 .addReg(Vec, RegState::Implicit); 386 387 LoadM0(MI, MovRel); 388 } 389 390 void SILowerControlFlowPass::IndirectDst(MachineInstr &MI) { 391 392 MachineBasicBlock &MBB = *MI.getParent(); 393 DebugLoc DL = MI.getDebugLoc(); 394 395 unsigned Dst = MI.getOperand(0).getReg(); 396 unsigned Off = MI.getOperand(4).getImm(); 397 unsigned Val = MI.getOperand(5).getReg(); 398 399 MachineInstr *MovRel = 400 BuildMI(*MBB.getParent(), DL, TII->get(AMDGPU::V_MOVRELD_B32_e32)) 401 .addReg(TRI->getSubReg(Dst, AMDGPU::sub0) + Off, RegState::Define) 402 .addReg(Val) 403 .addReg(AMDGPU::M0, RegState::Implicit) 404 .addReg(Dst, RegState::Implicit); 405 406 LoadM0(MI, MovRel); 407 } 408 409 bool SILowerControlFlowPass::runOnMachineFunction(MachineFunction &MF) { 410 411 bool HaveKill = false; 412 unsigned Depth = 0; 413 414 for (MachineFunction::iterator BI = MF.begin(), BE = MF.end(); 415 BI != BE; ++BI) { 416 417 MachineBasicBlock &MBB = *BI; 418 for (MachineBasicBlock::iterator I = MBB.begin(), Next = llvm::next(I); 419 I != MBB.end(); I = Next) { 420 421 Next = llvm::next(I); 422 MachineInstr &MI = *I; 423 switch (MI.getOpcode()) { 424 default: break; 425 case AMDGPU::SI_IF: 426 ++Depth; 427 If(MI); 428 break; 429 430 case AMDGPU::SI_ELSE: 431 Else(MI); 432 break; 433 434 case AMDGPU::SI_BREAK: 435 Break(MI); 436 break; 437 438 case AMDGPU::SI_IF_BREAK: 439 IfBreak(MI); 440 break; 441 442 case AMDGPU::SI_ELSE_BREAK: 443 ElseBreak(MI); 444 break; 445 446 case AMDGPU::SI_LOOP: 447 ++Depth; 448 Loop(MI); 449 break; 450 451 case AMDGPU::SI_END_CF: 452 if (--Depth == 0 && HaveKill) { 453 SkipIfDead(MI); 454 HaveKill = false; 455 } 456 EndCf(MI); 457 break; 458 459 case AMDGPU::SI_KILL: 460 if (Depth == 0) 461 SkipIfDead(MI); 462 else 463 HaveKill = true; 464 Kill(MI); 465 break; 466 467 case AMDGPU::S_BRANCH: 468 Branch(MI); 469 break; 470 471 case AMDGPU::SI_INDIRECT_SRC: 472 IndirectSrc(MI); 473 break; 474 475 case AMDGPU::SI_INDIRECT_DST_V2: 476 case AMDGPU::SI_INDIRECT_DST_V4: 477 case AMDGPU::SI_INDIRECT_DST_V8: 478 case AMDGPU::SI_INDIRECT_DST_V16: 479 IndirectDst(MI); 480 break; 481 } 482 } 483 } 484 485 return true; 486 } 487
