lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp

   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 || strcmp(Name, "__tls_align") == 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       std::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 MCOperand WebAssemblyMCInstLower::lowerTypeIndexOperand(
 167     SmallVector<wasm::ValType, 1> &&Returns,
 168     SmallVector<wasm::ValType, 4> &&Params) const {
 169   auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns),
 170                                                          std::move(Params));
 171   MCSymbol *Sym = Printer.createTempSymbol("typeindex");
 172   auto *WasmSym = cast<MCSymbolWasm>(Sym);
 173   WasmSym->setSignature(Signature.get());
 174   Printer.addSignature(std::move(Signature));
 175   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 176   const MCExpr *Expr =
 177       MCSymbolRefExpr::create(WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx);
 178   return MCOperand::createExpr(Expr);
 179 }
 180
 181 // Return the WebAssembly type associated with the given register class.
 182 static wasm::ValType getType(const TargetRegisterClass *RC) {
 183   if (RC == &WebAssembly::I32RegClass)
 184     return wasm::ValType::I32;
 185   if (RC == &WebAssembly::I64RegClass)
 186     return wasm::ValType::I64;
 187   if (RC == &WebAssembly::F32RegClass)
 188     return wasm::ValType::F32;
 189   if (RC == &WebAssembly::F64RegClass)
 190     return wasm::ValType::F64;
 191   if (RC == &WebAssembly::V128RegClass)
 192     return wasm::ValType::V128;
 193   llvm_unreachable("Unexpected register class");
 194 }
 195
 196 static void getFunctionReturns(const MachineInstr *MI,
 197                                SmallVectorImpl<wasm::ValType> &Returns) {
 198   const Function &F = MI->getMF()->getFunction();
 199   const TargetMachine &TM = MI->getMF()->getTarget();
 200   Type *RetTy = F.getReturnType();
 201   SmallVector<MVT, 4> CallerRetTys;
 202   computeLegalValueVTs(F, TM, RetTy, CallerRetTys);
 203   valTypesFromMVTs(CallerRetTys, Returns);
 204 }
 205
 206 void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
 207                                    MCInst &OutMI) const {
 208   OutMI.setOpcode(MI->getOpcode());
 209
 210   const MCInstrDesc &Desc = MI->getDesc();
 211   for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
 212     const MachineOperand &MO = MI->getOperand(I);
 213
 214     MCOperand MCOp;
 215     switch (MO.getType()) {
 216     default:
 217       MI->print(errs());
 218       llvm_unreachable("unknown operand type");
 219     case MachineOperand::MO_MachineBasicBlock:
 220       MI->print(errs());
 221       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
 222     case MachineOperand::MO_Register: {
 223       // Ignore all implicit register operands.
 224       if (MO.isImplicit())
 225         continue;
 226       const WebAssemblyFunctionInfo &MFI =
 227           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
 228       unsigned WAReg = MFI.getWAReg(MO.getReg());
 229       MCOp = MCOperand::createReg(WAReg);
 230       break;
 231     }
 232     case MachineOperand::MO_Immediate:
 233       if (I < Desc.NumOperands) {
 234         const MCOperandInfo &Info = Desc.OpInfo[I];
 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     case MachineOperand::MO_FPImmediate: {
 274       // TODO: MC converts all floating point immediate operands to double.
 275       // This is fine for numeric values, but may cause NaNs to change bits.
 276       const ConstantFP *Imm = MO.getFPImm();
 277       if (Imm->getType()->isFloatTy())
 278         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
 279       else if (Imm->getType()->isDoubleTy())
 280         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
 281       else
 282         llvm_unreachable("unknown floating point immediate type");
 283       break;
 284     }
 285     case MachineOperand::MO_GlobalAddress:
 286       MCOp = lowerSymbolOperand(MO, GetGlobalAddressSymbol(MO));
 287       break;
 288     case MachineOperand::MO_ExternalSymbol:
 289       // The target flag indicates whether this is a symbol for a
 290       // variable or a function.
 291       assert(MO.getTargetFlags() == 0 &&
 292              "WebAssembly uses only symbol flags on ExternalSymbols");
 293       MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
 294       break;
 295     case MachineOperand::MO_MCSymbol:
 296       // This is currently used only for LSDA symbols (GCC_except_table),
 297       // because global addresses or other external symbols are handled above.
 298       assert(MO.getTargetFlags() == 0 &&
 299              "WebAssembly does not use target flags on MCSymbol");
 300       MCOp = lowerSymbolOperand(MO, MO.getMCSymbol());
 301       break;
 302     }
 303
 304     OutMI.addOperand(MCOp);
 305   }
 306
 307   if (!WasmKeepRegisters)
 308     removeRegisterOperands(MI, OutMI);
 309 }
 310
 311 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) {
 312   // Remove all uses of stackified registers to bring the instruction format
 313   // into its final stack form used thruout MC, and transition opcodes to
 314   // their _S variant.
 315   // We do this seperate from the above code that still may need these
 316   // registers for e.g. call_indirect signatures.
 317   // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for
 318   // details.
 319   // TODO: the code above creates new registers which are then removed here.
 320   // That code could be slightly simplified by not doing that, though maybe
 321   // it is simpler conceptually to keep the code above in "register mode"
 322   // until this transition point.
 323   // FIXME: we are not processing inline assembly, which contains register
 324   // operands, because it is used by later target generic code.
 325   if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm())
 326     return;
 327
 328   // Transform to _S instruction.
 329   auto RegOpcode = OutMI.getOpcode();
 330   auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode);
 331   assert(StackOpcode != -1 && "Failed to stackify instruction");
 332   OutMI.setOpcode(StackOpcode);
 333
 334   // Remove register operands.
 335   for (auto I = OutMI.getNumOperands(); I; --I) {
 336     auto &MO = OutMI.getOperand(I - 1);
 337     if (MO.isReg()) {
 338       OutMI.erase(&MO);
 339     }
 340   }
 341 }