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 // 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           // return_call_indirect instructions have the return type of the
 230           // caller
 231           if (MI->getOpcode() == WebAssembly::RET_CALL_INDIRECT) {
 232             const Function &F = MI->getMF()->getFunction();
 233             const TargetMachine &TM = MI->getMF()->getTarget();
 234             Type *RetTy = F.getReturnType();
 235             SmallVector<MVT, 4> CallerRetTys;
 236             computeLegalValueVTs(F, TM, RetTy, CallerRetTys);
 237             valTypesFromMVTs(CallerRetTys, Returns);
 238           }
 239
 240           auto *WasmSym = cast<MCSymbolWasm>(Sym);
 241           auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns),
 242                                                             std::move(Params));
 243           WasmSym->setSignature(Signature.get());
 244           Printer.addSignature(std::move(Signature));
 245           WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 246
 247           const MCExpr *Expr = MCSymbolRefExpr::create(
 248               WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx);
 249           MCOp = MCOperand::createExpr(Expr);
 250           break;
 251         }
 252       }
 253       MCOp = MCOperand::createImm(MO.getImm());
 254       break;
 255     case MachineOperand::MO_FPImmediate: {
 256       // TODO: MC converts all floating point immediate operands to double.
 257       // This is fine for numeric values, but may cause NaNs to change bits.
 258       const ConstantFP *Imm = MO.getFPImm();
 259       if (Imm->getType()->isFloatTy())
 260         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
 261       else if (Imm->getType()->isDoubleTy())
 262         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
 263       else
 264         llvm_unreachable("unknown floating point immediate type");
 265       break;
 266     }
 267     case MachineOperand::MO_GlobalAddress:
 268       MCOp = lowerSymbolOperand(MO, GetGlobalAddressSymbol(MO));
 269       break;
 270     case MachineOperand::MO_ExternalSymbol:
 271       // The target flag indicates whether this is a symbol for a
 272       // variable or a function.
 273       assert(MO.getTargetFlags() == 0 &&
 274              "WebAssembly uses only symbol flags on ExternalSymbols");
 275       MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
 276       break;
 277     case MachineOperand::MO_MCSymbol:
 278       // This is currently used only for LSDA symbols (GCC_except_table),
 279       // because global addresses or other external symbols are handled above.
 280       assert(MO.getTargetFlags() == 0 &&
 281              "WebAssembly does not use target flags on MCSymbol");
 282       MCOp = lowerSymbolOperand(MO, MO.getMCSymbol());
 283       break;
 284     }
 285
 286     OutMI.addOperand(MCOp);
 287   }
 288
 289   if (!WasmKeepRegisters)
 290     removeRegisterOperands(MI, OutMI);
 291 }
 292
 293 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) {
 294   // Remove all uses of stackified registers to bring the instruction format
 295   // into its final stack form used thruout MC, and transition opcodes to
 296   // their _S variant.
 297   // We do this seperate from the above code that still may need these
 298   // registers for e.g. call_indirect signatures.
 299   // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for
 300   // details.
 301   // TODO: the code above creates new registers which are then removed here.
 302   // That code could be slightly simplified by not doing that, though maybe
 303   // it is simpler conceptually to keep the code above in "register mode"
 304   // until this transition point.
 305   // FIXME: we are not processing inline assembly, which contains register
 306   // operands, because it is used by later target generic code.
 307   if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm())
 308     return;
 309
 310   // Transform to _S instruction.
 311   auto RegOpcode = OutMI.getOpcode();
 312   auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode);
 313   assert(StackOpcode != -1 && "Failed to stackify instruction");
 314   OutMI.setOpcode(StackOpcode);
 315
 316   // Remove register operands.
 317   for (auto I = OutMI.getNumOperands(); I; --I) {
 318     auto &MO = OutMI.getOperand(I - 1);
 319     if (MO.isReg()) {
 320       OutMI.erase(&MO);
 321     }
 322   }
 323 }