1 //===-- WebAssemblyExplicitLocals.cpp - Make Locals Explicit --------------===// 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 /// \file 10 /// This file converts any remaining registers into WebAssembly locals. 11 /// 12 /// After register stackification and register coloring, convert non-stackified 13 /// registers into locals, inserting explicit local.get and local.set 14 /// instructions. 15 /// 16 //===----------------------------------------------------------------------===// 17 18 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 19 #include "WebAssembly.h" 20 #include "WebAssemblyDebugValueManager.h" 21 #include "WebAssemblyMachineFunctionInfo.h" 22 #include "WebAssemblySubtarget.h" 23 #include "WebAssemblyUtilities.h" 24 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 25 #include "llvm/CodeGen/MachineInstrBuilder.h" 26 #include "llvm/CodeGen/MachineRegisterInfo.h" 27 #include "llvm/CodeGen/Passes.h" 28 #include "llvm/Support/Debug.h" 29 #include "llvm/Support/raw_ostream.h" 30 using namespace llvm; 31 32 #define DEBUG_TYPE "wasm-explicit-locals" 33 34 namespace { 35 class WebAssemblyExplicitLocals final : public MachineFunctionPass { 36 StringRef getPassName() const override { 37 return "WebAssembly Explicit Locals"; 38 } 39 40 void getAnalysisUsage(AnalysisUsage &AU) const override { 41 AU.setPreservesCFG(); 42 AU.addPreserved<MachineBlockFrequencyInfo>(); 43 MachineFunctionPass::getAnalysisUsage(AU); 44 } 45 46 bool runOnMachineFunction(MachineFunction &MF) override; 47 48 public: 49 static char ID; // Pass identification, replacement for typeid 50 WebAssemblyExplicitLocals() : MachineFunctionPass(ID) {} 51 }; 52 } // end anonymous namespace 53 54 char WebAssemblyExplicitLocals::ID = 0; 55 INITIALIZE_PASS(WebAssemblyExplicitLocals, DEBUG_TYPE, 56 "Convert registers to WebAssembly locals", false, false) 57 58 FunctionPass *llvm::createWebAssemblyExplicitLocals() { 59 return new WebAssemblyExplicitLocals(); 60 } 61 62 static void checkFrameBase(WebAssemblyFunctionInfo &MFI, unsigned Local, 63 unsigned Reg) { 64 // Mark a local for the frame base vreg. 65 if (MFI.isFrameBaseVirtual() && Reg == MFI.getFrameBaseVreg()) { 66 LLVM_DEBUG({ 67 dbgs() << "Allocating local " << Local << "for VReg " 68 << Register::virtReg2Index(Reg) << '\n'; 69 }); 70 MFI.setFrameBaseLocal(Local); 71 } 72 } 73 74 /// Return a local id number for the given register, assigning it a new one 75 /// if it doesn't yet have one. 76 static unsigned getLocalId(DenseMap<unsigned, unsigned> &Reg2Local, 77 WebAssemblyFunctionInfo &MFI, unsigned &CurLocal, 78 unsigned Reg) { 79 auto P = Reg2Local.insert(std::make_pair(Reg, CurLocal)); 80 if (P.second) { 81 checkFrameBase(MFI, CurLocal, Reg); 82 ++CurLocal; 83 } 84 return P.first->second; 85 } 86 87 /// Get the appropriate drop opcode for the given register class. 88 static unsigned getDropOpcode(const TargetRegisterClass *RC) { 89 if (RC == &WebAssembly::I32RegClass) 90 return WebAssembly::DROP_I32; 91 if (RC == &WebAssembly::I64RegClass) 92 return WebAssembly::DROP_I64; 93 if (RC == &WebAssembly::F32RegClass) 94 return WebAssembly::DROP_F32; 95 if (RC == &WebAssembly::F64RegClass) 96 return WebAssembly::DROP_F64; 97 if (RC == &WebAssembly::V128RegClass) 98 return WebAssembly::DROP_V128; 99 if (RC == &WebAssembly::FUNCREFRegClass) 100 return WebAssembly::DROP_FUNCREF; 101 if (RC == &WebAssembly::EXTERNREFRegClass) 102 return WebAssembly::DROP_EXTERNREF; 103 llvm_unreachable("Unexpected register class"); 104 } 105 106 /// Get the appropriate local.get opcode for the given register class. 107 static unsigned getLocalGetOpcode(const TargetRegisterClass *RC) { 108 if (RC == &WebAssembly::I32RegClass) 109 return WebAssembly::LOCAL_GET_I32; 110 if (RC == &WebAssembly::I64RegClass) 111 return WebAssembly::LOCAL_GET_I64; 112 if (RC == &WebAssembly::F32RegClass) 113 return WebAssembly::LOCAL_GET_F32; 114 if (RC == &WebAssembly::F64RegClass) 115 return WebAssembly::LOCAL_GET_F64; 116 if (RC == &WebAssembly::V128RegClass) 117 return WebAssembly::LOCAL_GET_V128; 118 if (RC == &WebAssembly::FUNCREFRegClass) 119 return WebAssembly::LOCAL_GET_FUNCREF; 120 if (RC == &WebAssembly::EXTERNREFRegClass) 121 return WebAssembly::LOCAL_GET_EXTERNREF; 122 llvm_unreachable("Unexpected register class"); 123 } 124 125 /// Get the appropriate local.set opcode for the given register class. 126 static unsigned getLocalSetOpcode(const TargetRegisterClass *RC) { 127 if (RC == &WebAssembly::I32RegClass) 128 return WebAssembly::LOCAL_SET_I32; 129 if (RC == &WebAssembly::I64RegClass) 130 return WebAssembly::LOCAL_SET_I64; 131 if (RC == &WebAssembly::F32RegClass) 132 return WebAssembly::LOCAL_SET_F32; 133 if (RC == &WebAssembly::F64RegClass) 134 return WebAssembly::LOCAL_SET_F64; 135 if (RC == &WebAssembly::V128RegClass) 136 return WebAssembly::LOCAL_SET_V128; 137 if (RC == &WebAssembly::FUNCREFRegClass) 138 return WebAssembly::LOCAL_SET_FUNCREF; 139 if (RC == &WebAssembly::EXTERNREFRegClass) 140 return WebAssembly::LOCAL_SET_EXTERNREF; 141 llvm_unreachable("Unexpected register class"); 142 } 143 144 /// Get the appropriate local.tee opcode for the given register class. 145 static unsigned getLocalTeeOpcode(const TargetRegisterClass *RC) { 146 if (RC == &WebAssembly::I32RegClass) 147 return WebAssembly::LOCAL_TEE_I32; 148 if (RC == &WebAssembly::I64RegClass) 149 return WebAssembly::LOCAL_TEE_I64; 150 if (RC == &WebAssembly::F32RegClass) 151 return WebAssembly::LOCAL_TEE_F32; 152 if (RC == &WebAssembly::F64RegClass) 153 return WebAssembly::LOCAL_TEE_F64; 154 if (RC == &WebAssembly::V128RegClass) 155 return WebAssembly::LOCAL_TEE_V128; 156 if (RC == &WebAssembly::FUNCREFRegClass) 157 return WebAssembly::LOCAL_TEE_FUNCREF; 158 if (RC == &WebAssembly::EXTERNREFRegClass) 159 return WebAssembly::LOCAL_TEE_EXTERNREF; 160 llvm_unreachable("Unexpected register class"); 161 } 162 163 /// Get the type associated with the given register class. 164 static MVT typeForRegClass(const TargetRegisterClass *RC) { 165 if (RC == &WebAssembly::I32RegClass) 166 return MVT::i32; 167 if (RC == &WebAssembly::I64RegClass) 168 return MVT::i64; 169 if (RC == &WebAssembly::F32RegClass) 170 return MVT::f32; 171 if (RC == &WebAssembly::F64RegClass) 172 return MVT::f64; 173 if (RC == &WebAssembly::V128RegClass) 174 return MVT::v16i8; 175 if (RC == &WebAssembly::FUNCREFRegClass) 176 return MVT::funcref; 177 if (RC == &WebAssembly::EXTERNREFRegClass) 178 return MVT::externref; 179 llvm_unreachable("unrecognized register class"); 180 } 181 182 /// Given a MachineOperand of a stackified vreg, return the instruction at the 183 /// start of the expression tree. 184 static MachineInstr *findStartOfTree(MachineOperand &MO, 185 MachineRegisterInfo &MRI, 186 const WebAssemblyFunctionInfo &MFI) { 187 Register Reg = MO.getReg(); 188 assert(MFI.isVRegStackified(Reg)); 189 MachineInstr *Def = MRI.getVRegDef(Reg); 190 191 // If this instruction has any non-stackified defs, it is the start 192 for (auto DefReg : Def->defs()) { 193 if (!MFI.isVRegStackified(DefReg.getReg())) { 194 return Def; 195 } 196 } 197 198 // Find the first stackified use and proceed from there. 199 for (MachineOperand &DefMO : Def->explicit_uses()) { 200 if (!DefMO.isReg()) 201 continue; 202 return findStartOfTree(DefMO, MRI, MFI); 203 } 204 205 // If there were no stackified uses, we've reached the start. 206 return Def; 207 } 208 209 bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) { 210 LLVM_DEBUG(dbgs() << "********** Make Locals Explicit **********\n" 211 "********** Function: " 212 << MF.getName() << '\n'); 213 214 bool Changed = false; 215 MachineRegisterInfo &MRI = MF.getRegInfo(); 216 WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>(); 217 const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); 218 219 // Map non-stackified virtual registers to their local ids. 220 DenseMap<unsigned, unsigned> Reg2Local; 221 222 // Handle ARGUMENTS first to ensure that they get the designated numbers. 223 for (MachineBasicBlock::iterator I = MF.begin()->begin(), 224 E = MF.begin()->end(); 225 I != E;) { 226 MachineInstr &MI = *I++; 227 if (!WebAssembly::isArgument(MI.getOpcode())) 228 break; 229 Register Reg = MI.getOperand(0).getReg(); 230 assert(!MFI.isVRegStackified(Reg)); 231 auto Local = static_cast<unsigned>(MI.getOperand(1).getImm()); 232 Reg2Local[Reg] = Local; 233 checkFrameBase(MFI, Local, Reg); 234 235 // Update debug value to point to the local before removing. 236 WebAssemblyDebugValueManager(&MI).replaceWithLocal(Local); 237 238 MI.eraseFromParent(); 239 Changed = true; 240 } 241 242 // Start assigning local numbers after the last parameter and after any 243 // already-assigned locals. 244 unsigned CurLocal = static_cast<unsigned>(MFI.getParams().size()); 245 CurLocal += static_cast<unsigned>(MFI.getLocals().size()); 246 247 // Precompute the set of registers that are unused, so that we can insert 248 // drops to their defs. 249 BitVector UseEmpty(MRI.getNumVirtRegs()); 250 for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) 251 UseEmpty[I] = MRI.use_empty(Register::index2VirtReg(I)); 252 253 // Visit each instruction in the function. 254 for (MachineBasicBlock &MBB : MF) { 255 for (MachineInstr &MI : llvm::make_early_inc_range(MBB)) { 256 assert(!WebAssembly::isArgument(MI.getOpcode())); 257 258 if (MI.isDebugInstr() || MI.isLabel()) 259 continue; 260 261 if (MI.getOpcode() == WebAssembly::IMPLICIT_DEF) { 262 MI.eraseFromParent(); 263 Changed = true; 264 continue; 265 } 266 267 // Replace tee instructions with local.tee. The difference is that tee 268 // instructions have two defs, while local.tee instructions have one def 269 // and an index of a local to write to. 270 // 271 // - Before: 272 // TeeReg, Reg = TEE DefReg 273 // INST ..., TeeReg, ... 274 // INST ..., Reg, ... 275 // INST ..., Reg, ... 276 // * DefReg: may or may not be stackified 277 // * Reg: not stackified 278 // * TeeReg: stackified 279 // 280 // - After (when DefReg was already stackified): 281 // TeeReg = LOCAL_TEE LocalId1, DefReg 282 // INST ..., TeeReg, ... 283 // INST ..., Reg, ... 284 // INST ..., Reg, ... 285 // * Reg: mapped to LocalId1 286 // * TeeReg: stackified 287 // 288 // - After (when DefReg was not already stackified): 289 // NewReg = LOCAL_GET LocalId1 290 // TeeReg = LOCAL_TEE LocalId2, NewReg 291 // INST ..., TeeReg, ... 292 // INST ..., Reg, ... 293 // INST ..., Reg, ... 294 // * DefReg: mapped to LocalId1 295 // * Reg: mapped to LocalId2 296 // * TeeReg: stackified 297 if (WebAssembly::isTee(MI.getOpcode())) { 298 assert(MFI.isVRegStackified(MI.getOperand(0).getReg())); 299 assert(!MFI.isVRegStackified(MI.getOperand(1).getReg())); 300 Register DefReg = MI.getOperand(2).getReg(); 301 const TargetRegisterClass *RC = MRI.getRegClass(DefReg); 302 303 // Stackify the input if it isn't stackified yet. 304 if (!MFI.isVRegStackified(DefReg)) { 305 unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, DefReg); 306 Register NewReg = MRI.createVirtualRegister(RC); 307 unsigned Opc = getLocalGetOpcode(RC); 308 BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(Opc), NewReg) 309 .addImm(LocalId); 310 MI.getOperand(2).setReg(NewReg); 311 MFI.stackifyVReg(MRI, NewReg); 312 } 313 314 // Replace the TEE with a LOCAL_TEE. 315 unsigned LocalId = 316 getLocalId(Reg2Local, MFI, CurLocal, MI.getOperand(1).getReg()); 317 unsigned Opc = getLocalTeeOpcode(RC); 318 BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(Opc), 319 MI.getOperand(0).getReg()) 320 .addImm(LocalId) 321 .addReg(MI.getOperand(2).getReg()); 322 323 WebAssemblyDebugValueManager(&MI).replaceWithLocal(LocalId); 324 325 MI.eraseFromParent(); 326 Changed = true; 327 continue; 328 } 329 330 // Insert local.sets for any defs that aren't stackified yet. 331 for (auto &Def : MI.defs()) { 332 Register OldReg = Def.getReg(); 333 if (!MFI.isVRegStackified(OldReg)) { 334 const TargetRegisterClass *RC = MRI.getRegClass(OldReg); 335 Register NewReg = MRI.createVirtualRegister(RC); 336 auto InsertPt = std::next(MI.getIterator()); 337 if (UseEmpty[Register::virtReg2Index(OldReg)]) { 338 unsigned Opc = getDropOpcode(RC); 339 MachineInstr *Drop = 340 BuildMI(MBB, InsertPt, MI.getDebugLoc(), TII->get(Opc)) 341 .addReg(NewReg); 342 // After the drop instruction, this reg operand will not be used 343 Drop->getOperand(0).setIsKill(); 344 if (MFI.isFrameBaseVirtual() && OldReg == MFI.getFrameBaseVreg()) 345 MFI.clearFrameBaseVreg(); 346 } else { 347 unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, OldReg); 348 unsigned Opc = getLocalSetOpcode(RC); 349 350 WebAssemblyDebugValueManager(&MI).replaceWithLocal(LocalId); 351 352 BuildMI(MBB, InsertPt, MI.getDebugLoc(), TII->get(Opc)) 353 .addImm(LocalId) 354 .addReg(NewReg); 355 } 356 // This register operand of the original instruction is now being used 357 // by the inserted drop or local.set instruction, so make it not dead 358 // yet. 359 Def.setReg(NewReg); 360 Def.setIsDead(false); 361 MFI.stackifyVReg(MRI, NewReg); 362 Changed = true; 363 } 364 } 365 366 // Insert local.gets for any uses that aren't stackified yet. 367 MachineInstr *InsertPt = &MI; 368 for (MachineOperand &MO : reverse(MI.explicit_uses())) { 369 if (!MO.isReg()) 370 continue; 371 372 Register OldReg = MO.getReg(); 373 374 // Inline asm may have a def in the middle of the operands. Our contract 375 // with inline asm register operands is to provide local indices as 376 // immediates. 377 if (MO.isDef()) { 378 assert(MI.isInlineAsm()); 379 unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, OldReg); 380 // If this register operand is tied to another operand, we can't 381 // change it to an immediate. Untie it first. 382 MI.untieRegOperand(MO.getOperandNo()); 383 MO.ChangeToImmediate(LocalId); 384 continue; 385 } 386 387 // If we see a stackified register, prepare to insert subsequent 388 // local.gets before the start of its tree. 389 if (MFI.isVRegStackified(OldReg)) { 390 InsertPt = findStartOfTree(MO, MRI, MFI); 391 continue; 392 } 393 394 // Our contract with inline asm register operands is to provide local 395 // indices as immediates. 396 if (MI.isInlineAsm()) { 397 unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, OldReg); 398 // Untie it first if this reg operand is tied to another operand. 399 MI.untieRegOperand(MO.getOperandNo()); 400 MO.ChangeToImmediate(LocalId); 401 continue; 402 } 403 404 // Insert a local.get. 405 unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, OldReg); 406 const TargetRegisterClass *RC = MRI.getRegClass(OldReg); 407 Register NewReg = MRI.createVirtualRegister(RC); 408 unsigned Opc = getLocalGetOpcode(RC); 409 // Use a InsertPt as our DebugLoc, since MI may be discontinuous from 410 // the where this local is being inserted, causing non-linear stepping 411 // in the debugger or function entry points where variables aren't live 412 // yet. Alternative is previous instruction, but that is strictly worse 413 // since it can point at the previous statement. 414 // See crbug.com/1251909, crbug.com/1249745 415 InsertPt = BuildMI(MBB, InsertPt, InsertPt->getDebugLoc(), 416 TII->get(Opc), NewReg).addImm(LocalId); 417 MO.setReg(NewReg); 418 MFI.stackifyVReg(MRI, NewReg); 419 Changed = true; 420 } 421 422 // Coalesce and eliminate COPY instructions. 423 if (WebAssembly::isCopy(MI.getOpcode())) { 424 MRI.replaceRegWith(MI.getOperand(1).getReg(), 425 MI.getOperand(0).getReg()); 426 MI.eraseFromParent(); 427 Changed = true; 428 } 429 } 430 } 431 432 // Define the locals. 433 // TODO: Sort the locals for better compression. 434 MFI.setNumLocals(CurLocal - MFI.getParams().size()); 435 for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) { 436 Register Reg = Register::index2VirtReg(I); 437 auto RL = Reg2Local.find(Reg); 438 if (RL == Reg2Local.end() || RL->second < MFI.getParams().size()) 439 continue; 440 441 MFI.setLocal(RL->second - MFI.getParams().size(), 442 typeForRegClass(MRI.getRegClass(Reg))); 443 Changed = true; 444 } 445 446 #ifndef NDEBUG 447 // Assert that all registers have been stackified at this point. 448 for (const MachineBasicBlock &MBB : MF) { 449 for (const MachineInstr &MI : MBB) { 450 if (MI.isDebugInstr() || MI.isLabel()) 451 continue; 452 for (const MachineOperand &MO : MI.explicit_operands()) { 453 assert( 454 (!MO.isReg() || MRI.use_empty(MO.getReg()) || 455 MFI.isVRegStackified(MO.getReg())) && 456 "WebAssemblyExplicitLocals failed to stackify a register operand"); 457 } 458 } 459 } 460 #endif 461 462 return Changed; 463 } 464