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