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