1 // WebAssemblyMCInstLower.cpp - Convert WebAssembly MachineInstr to an MCInst // 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 contains code to lower WebAssembly MachineInstrs to their 11 /// corresponding MCInst records. 12 /// 13 //===----------------------------------------------------------------------===// 14 15 #include "WebAssemblyMCInstLower.h" 16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 17 #include "TargetInfo/WebAssemblyTargetInfo.h" 18 #include "WebAssemblyAsmPrinter.h" 19 #include "WebAssemblyMachineFunctionInfo.h" 20 #include "WebAssemblyRuntimeLibcallSignatures.h" 21 #include "llvm/CodeGen/AsmPrinter.h" 22 #include "llvm/CodeGen/MachineFunction.h" 23 #include "llvm/IR/Constants.h" 24 #include "llvm/MC/MCAsmInfo.h" 25 #include "llvm/MC/MCContext.h" 26 #include "llvm/MC/MCExpr.h" 27 #include "llvm/MC/MCInst.h" 28 #include "llvm/MC/MCSymbolWasm.h" 29 #include "llvm/Support/ErrorHandling.h" 30 #include "llvm/Support/raw_ostream.h" 31 using namespace llvm; 32 33 // This disables the removal of registers when lowering into MC, as required 34 // by some current tests. 35 cl::opt<bool> 36 WasmKeepRegisters("wasm-keep-registers", cl::Hidden, 37 cl::desc("WebAssembly: output stack registers in" 38 " instruction output for test purposes only."), 39 cl::init(false)); 40 41 extern cl::opt<bool> EnableEmException; 42 extern cl::opt<bool> EnableEmSjLj; 43 44 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI); 45 46 MCSymbol * 47 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const { 48 const GlobalValue *Global = MO.getGlobal(); 49 if (!isa<Function>(Global)) 50 return cast<MCSymbolWasm>(Printer.getSymbol(Global)); 51 52 const auto *FuncTy = cast<FunctionType>(Global->getValueType()); 53 const MachineFunction &MF = *MO.getParent()->getParent()->getParent(); 54 const TargetMachine &TM = MF.getTarget(); 55 const Function &CurrentFunc = MF.getFunction(); 56 57 SmallVector<MVT, 1> ResultMVTs; 58 SmallVector<MVT, 4> ParamMVTs; 59 const auto *const F = dyn_cast<Function>(Global); 60 computeSignatureVTs(FuncTy, F, CurrentFunc, TM, ParamMVTs, ResultMVTs); 61 auto Signature = signatureFromMVTs(ResultMVTs, ParamMVTs); 62 63 bool InvokeDetected = false; 64 auto *WasmSym = Printer.getMCSymbolForFunction( 65 F, EnableEmException || EnableEmSjLj, Signature.get(), InvokeDetected); 66 WasmSym->setSignature(Signature.get()); 67 Printer.addSignature(std::move(Signature)); 68 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION); 69 return WasmSym; 70 } 71 72 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol( 73 const MachineOperand &MO) const { 74 const char *Name = MO.getSymbolName(); 75 auto *WasmSym = cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name)); 76 const WebAssemblySubtarget &Subtarget = Printer.getSubtarget(); 77 78 // Except for certain known symbols, all symbols used by CodeGen are 79 // functions. It's OK to hardcode knowledge of specific symbols here; this 80 // method is precisely there for fetching the signatures of known 81 // Clang-provided symbols. 82 if (strcmp(Name, "__stack_pointer") == 0 || strcmp(Name, "__tls_base") == 0 || 83 strcmp(Name, "__memory_base") == 0 || strcmp(Name, "__table_base") == 0 || 84 strcmp(Name, "__tls_size") == 0 || strcmp(Name, "__tls_align") == 0) { 85 bool Mutable = 86 strcmp(Name, "__stack_pointer") == 0 || strcmp(Name, "__tls_base") == 0; 87 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL); 88 WasmSym->setGlobalType(wasm::WasmGlobalType{ 89 uint8_t(Subtarget.hasAddr64() && strcmp(Name, "__table_base") != 0 90 ? wasm::WASM_TYPE_I64 91 : wasm::WASM_TYPE_I32), 92 Mutable}); 93 return WasmSym; 94 } 95 96 SmallVector<wasm::ValType, 4> Returns; 97 SmallVector<wasm::ValType, 4> Params; 98 if (strcmp(Name, "__cpp_exception") == 0) { 99 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT); 100 // We can't confirm its signature index for now because there can be 101 // imported exceptions. Set it to be 0 for now. 102 WasmSym->setEventType( 103 {wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0}); 104 // We may have multiple C++ compilation units to be linked together, each of 105 // which defines the exception symbol. To resolve them, we declare them as 106 // weak. 107 WasmSym->setWeak(true); 108 WasmSym->setExternal(true); 109 110 // All C++ exceptions are assumed to have a single i32 (for wasm32) or i64 111 // (for wasm64) param type and void return type. The reaon is, all C++ 112 // exception values are pointers, and to share the type section with 113 // functions, exceptions are assumed to have void return type. 114 Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64 115 : wasm::ValType::I32); 116 } else { // Function symbols 117 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION); 118 getLibcallSignature(Subtarget, Name, Returns, Params); 119 } 120 auto Signature = 121 std::make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params)); 122 WasmSym->setSignature(Signature.get()); 123 Printer.addSignature(std::move(Signature)); 124 125 return WasmSym; 126 } 127 128 MCOperand WebAssemblyMCInstLower::lowerSymbolOperand(const MachineOperand &MO, 129 MCSymbol *Sym) const { 130 MCSymbolRefExpr::VariantKind Kind = MCSymbolRefExpr::VK_None; 131 unsigned TargetFlags = MO.getTargetFlags(); 132 133 switch (TargetFlags) { 134 case WebAssemblyII::MO_NO_FLAG: 135 break; 136 case WebAssemblyII::MO_GOT: 137 Kind = MCSymbolRefExpr::VK_GOT; 138 break; 139 case WebAssemblyII::MO_MEMORY_BASE_REL: 140 Kind = MCSymbolRefExpr::VK_WASM_MBREL; 141 break; 142 case WebAssemblyII::MO_TLS_BASE_REL: 143 Kind = MCSymbolRefExpr::VK_WASM_TLSREL; 144 break; 145 case WebAssemblyII::MO_TABLE_BASE_REL: 146 Kind = MCSymbolRefExpr::VK_WASM_TBREL; 147 break; 148 default: 149 llvm_unreachable("Unknown target flag on GV operand"); 150 } 151 152 const MCExpr *Expr = MCSymbolRefExpr::create(Sym, Kind, Ctx); 153 154 if (MO.getOffset() != 0) { 155 const auto *WasmSym = cast<MCSymbolWasm>(Sym); 156 if (TargetFlags == WebAssemblyII::MO_GOT) 157 report_fatal_error("GOT symbol references do not support offsets"); 158 if (WasmSym->isFunction()) 159 report_fatal_error("Function addresses with offsets not supported"); 160 if (WasmSym->isGlobal()) 161 report_fatal_error("Global indexes with offsets not supported"); 162 if (WasmSym->isEvent()) 163 report_fatal_error("Event indexes with offsets not supported"); 164 165 Expr = MCBinaryExpr::createAdd( 166 Expr, MCConstantExpr::create(MO.getOffset(), Ctx), Ctx); 167 } 168 169 return MCOperand::createExpr(Expr); 170 } 171 172 MCOperand WebAssemblyMCInstLower::lowerTypeIndexOperand( 173 SmallVector<wasm::ValType, 1> &&Returns, 174 SmallVector<wasm::ValType, 4> &&Params) const { 175 auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns), 176 std::move(Params)); 177 MCSymbol *Sym = Printer.createTempSymbol("typeindex"); 178 auto *WasmSym = cast<MCSymbolWasm>(Sym); 179 WasmSym->setSignature(Signature.get()); 180 Printer.addSignature(std::move(Signature)); 181 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION); 182 const MCExpr *Expr = 183 MCSymbolRefExpr::create(WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx); 184 return MCOperand::createExpr(Expr); 185 } 186 187 // Return the WebAssembly type associated with the given register class. 188 static wasm::ValType getType(const TargetRegisterClass *RC) { 189 if (RC == &WebAssembly::I32RegClass) 190 return wasm::ValType::I32; 191 if (RC == &WebAssembly::I64RegClass) 192 return wasm::ValType::I64; 193 if (RC == &WebAssembly::F32RegClass) 194 return wasm::ValType::F32; 195 if (RC == &WebAssembly::F64RegClass) 196 return wasm::ValType::F64; 197 if (RC == &WebAssembly::V128RegClass) 198 return wasm::ValType::V128; 199 llvm_unreachable("Unexpected register class"); 200 } 201 202 static void getFunctionReturns(const MachineInstr *MI, 203 SmallVectorImpl<wasm::ValType> &Returns) { 204 const Function &F = MI->getMF()->getFunction(); 205 const TargetMachine &TM = MI->getMF()->getTarget(); 206 Type *RetTy = F.getReturnType(); 207 SmallVector<MVT, 4> CallerRetTys; 208 computeLegalValueVTs(F, TM, RetTy, CallerRetTys); 209 valTypesFromMVTs(CallerRetTys, Returns); 210 } 211 212 void WebAssemblyMCInstLower::lower(const MachineInstr *MI, 213 MCInst &OutMI) const { 214 OutMI.setOpcode(MI->getOpcode()); 215 216 const MCInstrDesc &Desc = MI->getDesc(); 217 unsigned NumVariadicDefs = MI->getNumExplicitDefs() - Desc.getNumDefs(); 218 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) { 219 const MachineOperand &MO = MI->getOperand(I); 220 221 MCOperand MCOp; 222 switch (MO.getType()) { 223 default: 224 MI->print(errs()); 225 llvm_unreachable("unknown operand type"); 226 case MachineOperand::MO_MachineBasicBlock: 227 MI->print(errs()); 228 llvm_unreachable("MachineBasicBlock operand should have been rewritten"); 229 case MachineOperand::MO_Register: { 230 // Ignore all implicit register operands. 231 if (MO.isImplicit()) 232 continue; 233 const WebAssemblyFunctionInfo &MFI = 234 *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>(); 235 unsigned WAReg = MFI.getWAReg(MO.getReg()); 236 MCOp = MCOperand::createReg(WAReg); 237 break; 238 } 239 case MachineOperand::MO_Immediate: { 240 unsigned DescIndex = I - NumVariadicDefs; 241 if (DescIndex < Desc.NumOperands) { 242 const MCOperandInfo &Info = Desc.OpInfo[DescIndex]; 243 if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) { 244 SmallVector<wasm::ValType, 4> Returns; 245 SmallVector<wasm::ValType, 4> Params; 246 247 const MachineRegisterInfo &MRI = 248 MI->getParent()->getParent()->getRegInfo(); 249 for (const MachineOperand &MO : MI->defs()) 250 Returns.push_back(getType(MRI.getRegClass(MO.getReg()))); 251 for (const MachineOperand &MO : MI->explicit_uses()) 252 if (MO.isReg()) 253 Params.push_back(getType(MRI.getRegClass(MO.getReg()))); 254 255 // call_indirect instructions have a callee operand at the end which 256 // doesn't count as a param. 257 if (WebAssembly::isCallIndirect(MI->getOpcode())) 258 Params.pop_back(); 259 260 // return_call_indirect instructions have the return type of the 261 // caller 262 if (MI->getOpcode() == WebAssembly::RET_CALL_INDIRECT) 263 getFunctionReturns(MI, Returns); 264 265 MCOp = lowerTypeIndexOperand(std::move(Returns), std::move(Params)); 266 break; 267 } else if (Info.OperandType == WebAssembly::OPERAND_SIGNATURE) { 268 auto BT = static_cast<WebAssembly::BlockType>(MO.getImm()); 269 assert(BT != WebAssembly::BlockType::Invalid); 270 if (BT == WebAssembly::BlockType::Multivalue) { 271 SmallVector<wasm::ValType, 1> Returns; 272 getFunctionReturns(MI, Returns); 273 MCOp = lowerTypeIndexOperand(std::move(Returns), 274 SmallVector<wasm::ValType, 4>()); 275 break; 276 } 277 } else if (Info.OperandType == WebAssembly::OPERAND_HEAPTYPE) { 278 assert(static_cast<WebAssembly::HeapType>(MO.getImm()) != 279 WebAssembly::HeapType::Invalid); 280 // With typed function references, this will need a case for type 281 // index operands. Otherwise, fall through. 282 } 283 } 284 MCOp = MCOperand::createImm(MO.getImm()); 285 break; 286 } 287 case MachineOperand::MO_FPImmediate: { 288 // TODO: MC converts all floating point immediate operands to double. 289 // This is fine for numeric values, but may cause NaNs to change bits. 290 const ConstantFP *Imm = MO.getFPImm(); 291 if (Imm->getType()->isFloatTy()) 292 MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat()); 293 else if (Imm->getType()->isDoubleTy()) 294 MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble()); 295 else 296 llvm_unreachable("unknown floating point immediate type"); 297 break; 298 } 299 case MachineOperand::MO_GlobalAddress: 300 MCOp = lowerSymbolOperand(MO, GetGlobalAddressSymbol(MO)); 301 break; 302 case MachineOperand::MO_ExternalSymbol: 303 // The target flag indicates whether this is a symbol for a 304 // variable or a function. 305 assert(MO.getTargetFlags() == 0 && 306 "WebAssembly uses only symbol flags on ExternalSymbols"); 307 MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO)); 308 break; 309 case MachineOperand::MO_MCSymbol: 310 // This is currently used only for LSDA symbols (GCC_except_table), 311 // because global addresses or other external symbols are handled above. 312 assert(MO.getTargetFlags() == 0 && 313 "WebAssembly does not use target flags on MCSymbol"); 314 MCOp = lowerSymbolOperand(MO, MO.getMCSymbol()); 315 break; 316 } 317 318 OutMI.addOperand(MCOp); 319 } 320 321 if (!WasmKeepRegisters) 322 removeRegisterOperands(MI, OutMI); 323 else if (Desc.variadicOpsAreDefs()) 324 OutMI.insert(OutMI.begin(), MCOperand::createImm(MI->getNumExplicitDefs())); 325 } 326 327 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) { 328 // Remove all uses of stackified registers to bring the instruction format 329 // into its final stack form used thruout MC, and transition opcodes to 330 // their _S variant. 331 // We do this separate from the above code that still may need these 332 // registers for e.g. call_indirect signatures. 333 // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for 334 // details. 335 // TODO: the code above creates new registers which are then removed here. 336 // That code could be slightly simplified by not doing that, though maybe 337 // it is simpler conceptually to keep the code above in "register mode" 338 // until this transition point. 339 // FIXME: we are not processing inline assembly, which contains register 340 // operands, because it is used by later target generic code. 341 if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm()) 342 return; 343 344 // Transform to _S instruction. 345 auto RegOpcode = OutMI.getOpcode(); 346 auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode); 347 assert(StackOpcode != -1 && "Failed to stackify instruction"); 348 OutMI.setOpcode(StackOpcode); 349 350 // Remove register operands. 351 for (auto I = OutMI.getNumOperands(); I; --I) { 352 auto &MO = OutMI.getOperand(I - 1); 353 if (MO.isReg()) { 354 OutMI.erase(&MO); 355 } 356 } 357 } 358