1 // WebAssemblyMCInstLower.cpp - Convert WebAssembly MachineInstr to an MCInst // 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 /// This file contains code to lower WebAssembly MachineInstrs to their 12 /// corresponding MCInst records. 13 /// 14 //===----------------------------------------------------------------------===// 15 16 #include "WebAssemblyMCInstLower.h" 17 #include "WebAssemblyAsmPrinter.h" 18 #include "WebAssemblyMachineFunctionInfo.h" 19 #include "WebAssemblyRuntimeLibcallSignatures.h" 20 #include "WebAssemblyUtilities.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 // Defines llvm::WebAssembly::getStackOpcode to convert register instructions to 34 // stack instructions 35 #define GET_INSTRMAP_INFO 1 36 #include "WebAssemblyGenInstrInfo.inc" 37 38 // This disables the removal of registers when lowering into MC, as required 39 // by some current tests. 40 static cl::opt<bool> 41 WasmKeepRegisters("wasm-keep-registers", cl::Hidden, 42 cl::desc("WebAssembly: output stack registers in" 43 " instruction output for test purposes only."), 44 cl::init(false)); 45 46 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI); 47 48 MCSymbol * 49 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const { 50 const GlobalValue *Global = MO.getGlobal(); 51 MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global)); 52 53 if (const auto *FuncTy = dyn_cast<FunctionType>(Global->getValueType())) { 54 const MachineFunction &MF = *MO.getParent()->getParent()->getParent(); 55 const TargetMachine &TM = MF.getTarget(); 56 const Function &CurrentFunc = MF.getFunction(); 57 58 SmallVector<MVT, 1> ResultMVTs; 59 SmallVector<MVT, 4> ParamMVTs; 60 ComputeSignatureVTs(FuncTy, CurrentFunc, TM, ParamMVTs, ResultMVTs); 61 62 auto Signature = SignatureFromMVTs(ResultMVTs, ParamMVTs); 63 WasmSym->setSignature(Signature.get()); 64 Printer.addSignature(std::move(Signature)); 65 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION); 66 } 67 68 return WasmSym; 69 } 70 71 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol( 72 const MachineOperand &MO) const { 73 const char *Name = MO.getSymbolName(); 74 MCSymbolWasm *WasmSym = 75 cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name)); 76 const WebAssemblySubtarget &Subtarget = Printer.getSubtarget(); 77 78 // Except for the two exceptions (__stack_pointer and __cpp_exception), all 79 // other external symbols used by CodeGen are functions. It's OK to hardcode 80 // knowledge of specific symbols here; this method is precisely there for 81 // fetching the signatures of known Clang-provided symbols. 82 if (strcmp(Name, "__stack_pointer") == 0) { 83 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL); 84 WasmSym->setGlobalType(wasm::WasmGlobalType{ 85 uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64 86 : wasm::WASM_TYPE_I32), 87 true}); 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 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(MCSymbol *Sym, 124 int64_t Offset, 125 bool IsFunc, bool IsGlob, 126 bool IsEvent) const { 127 MCSymbolRefExpr::VariantKind VK = 128 IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION 129 : IsGlob ? MCSymbolRefExpr::VK_WebAssembly_GLOBAL 130 : IsEvent ? MCSymbolRefExpr::VK_WebAssembly_EVENT 131 : MCSymbolRefExpr::VK_None; 132 133 const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx); 134 135 if (Offset != 0) { 136 if (IsFunc) 137 report_fatal_error("Function addresses with offsets not supported"); 138 if (IsGlob) 139 report_fatal_error("Global indexes with offsets not supported"); 140 if (IsEvent) 141 report_fatal_error("Event indexes with offsets not supported"); 142 Expr = 143 MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx); 144 } 145 146 return MCOperand::createExpr(Expr); 147 } 148 149 // Return the WebAssembly type associated with the given register class. 150 static wasm::ValType getType(const TargetRegisterClass *RC) { 151 if (RC == &WebAssembly::I32RegClass) 152 return wasm::ValType::I32; 153 if (RC == &WebAssembly::I64RegClass) 154 return wasm::ValType::I64; 155 if (RC == &WebAssembly::F32RegClass) 156 return wasm::ValType::F32; 157 if (RC == &WebAssembly::F64RegClass) 158 return wasm::ValType::F64; 159 if (RC == &WebAssembly::V128RegClass) 160 return wasm::ValType::V128; 161 llvm_unreachable("Unexpected register class"); 162 } 163 164 void WebAssemblyMCInstLower::Lower(const MachineInstr *MI, 165 MCInst &OutMI) const { 166 OutMI.setOpcode(MI->getOpcode()); 167 168 const MCInstrDesc &Desc = MI->getDesc(); 169 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { 170 const MachineOperand &MO = MI->getOperand(i); 171 172 MCOperand MCOp; 173 switch (MO.getType()) { 174 default: 175 MI->print(errs()); 176 llvm_unreachable("unknown operand type"); 177 case MachineOperand::MO_MachineBasicBlock: 178 MI->print(errs()); 179 llvm_unreachable("MachineBasicBlock operand should have been rewritten"); 180 case MachineOperand::MO_Register: { 181 // Ignore all implicit register operands. 182 if (MO.isImplicit()) 183 continue; 184 const WebAssemblyFunctionInfo &MFI = 185 *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>(); 186 unsigned WAReg = MFI.getWAReg(MO.getReg()); 187 MCOp = MCOperand::createReg(WAReg); 188 break; 189 } 190 case MachineOperand::MO_Immediate: 191 if (i < Desc.NumOperands) { 192 const MCOperandInfo &Info = Desc.OpInfo[i]; 193 if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) { 194 MCSymbol *Sym = Printer.createTempSymbol("typeindex"); 195 196 SmallVector<wasm::ValType, 4> Returns; 197 SmallVector<wasm::ValType, 4> Params; 198 199 const MachineRegisterInfo &MRI = 200 MI->getParent()->getParent()->getRegInfo(); 201 for (const MachineOperand &MO : MI->defs()) 202 Returns.push_back(getType(MRI.getRegClass(MO.getReg()))); 203 for (const MachineOperand &MO : MI->explicit_uses()) 204 if (MO.isReg()) 205 Params.push_back(getType(MRI.getRegClass(MO.getReg()))); 206 207 // call_indirect instructions have a callee operand at the end which 208 // doesn't count as a param. 209 if (WebAssembly::isCallIndirect(*MI)) 210 Params.pop_back(); 211 212 MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym); 213 auto Signature = make_unique<wasm::WasmSignature>(std::move(Returns), 214 std::move(Params)); 215 WasmSym->setSignature(Signature.get()); 216 Printer.addSignature(std::move(Signature)); 217 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION); 218 219 const MCExpr *Expr = MCSymbolRefExpr::create( 220 WasmSym, MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX, Ctx); 221 MCOp = MCOperand::createExpr(Expr); 222 break; 223 } 224 } 225 MCOp = MCOperand::createImm(MO.getImm()); 226 break; 227 case MachineOperand::MO_FPImmediate: { 228 // TODO: MC converts all floating point immediate operands to double. 229 // This is fine for numeric values, but may cause NaNs to change bits. 230 const ConstantFP *Imm = MO.getFPImm(); 231 if (Imm->getType()->isFloatTy()) 232 MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat()); 233 else if (Imm->getType()->isDoubleTy()) 234 MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble()); 235 else 236 llvm_unreachable("unknown floating point immediate type"); 237 break; 238 } 239 case MachineOperand::MO_GlobalAddress: 240 assert(MO.getTargetFlags() == WebAssemblyII::MO_NO_FLAG && 241 "WebAssembly does not use target flags on GlobalAddresses"); 242 MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(), 243 MO.getGlobal()->getValueType()->isFunctionTy(), 244 false, false); 245 break; 246 case MachineOperand::MO_ExternalSymbol: 247 // The target flag indicates whether this is a symbol for a 248 // variable or a function. 249 assert((MO.getTargetFlags() & ~WebAssemblyII::MO_SYMBOL_MASK) == 0 && 250 "WebAssembly uses only symbol flags on ExternalSymbols"); 251 MCOp = LowerSymbolOperand( 252 GetExternalSymbolSymbol(MO), /*Offset=*/0, 253 (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_FUNCTION) != 0, 254 (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_GLOBAL) != 0, 255 (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_EVENT) != 0); 256 break; 257 case MachineOperand::MO_MCSymbol: 258 // This is currently used only for LSDA symbols (GCC_except_table), 259 // because global addresses or other external symbols are handled above. 260 assert(MO.getTargetFlags() == 0 && 261 "WebAssembly does not use target flags on MCSymbol"); 262 MCOp = LowerSymbolOperand(MO.getMCSymbol(), /*Offset=*/0, false, false, 263 false); 264 break; 265 } 266 267 OutMI.addOperand(MCOp); 268 } 269 270 if (!WasmKeepRegisters) 271 removeRegisterOperands(MI, OutMI); 272 } 273 274 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) { 275 // Remove all uses of stackified registers to bring the instruction format 276 // into its final stack form used thruout MC, and transition opcodes to 277 // their _S variant. 278 // We do this seperate from the above code that still may need these 279 // registers for e.g. call_indirect signatures. 280 // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for 281 // details. 282 // TODO: the code above creates new registers which are then removed here. 283 // That code could be slightly simplified by not doing that, though maybe 284 // it is simpler conceptually to keep the code above in "register mode" 285 // until this transition point. 286 // FIXME: we are not processing inline assembly, which contains register 287 // operands, because it is used by later target generic code. 288 if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm()) 289 return; 290 291 // Transform to _S instruction. 292 auto RegOpcode = OutMI.getOpcode(); 293 auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode); 294 assert(StackOpcode != -1 && "Failed to stackify instruction"); 295 OutMI.setOpcode(StackOpcode); 296 297 // Remove register operands. 298 for (auto I = OutMI.getNumOperands(); I; --I) { 299 auto &MO = OutMI.getOperand(I - 1); 300 if (MO.isReg()) { 301 OutMI.erase(&MO); 302 } 303 } 304 } 305