WebAssemblyMCInstLower.cpp

// WebAssemblyMCInstLower.cpp - Convert WebAssembly MachineInstr to an MCInst //
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file contains code to lower WebAssembly MachineInstrs to their
/// corresponding MCInst records.
///
//===----------------------------------------------------------------------===//

#include "WebAssemblyMCInstLower.h"
#include "TargetInfo/WebAssemblyTargetInfo.h"
#include "Utils/WebAssemblyTypeUtilities.h"
#include "Utils/WebAssemblyUtilities.h"
#include "WebAssemblyAsmPrinter.h"
#include "WebAssemblyISelLowering.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/IR/Constants.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;

// This disables the removal of registers when lowering into MC, as required
// by some current tests.
cl::opt<bool>
    WasmKeepRegisters("wasm-keep-registers", cl::Hidden,
                      cl::desc("WebAssembly: output stack registers in"
                               " instruction output for test purposes only."),
                      cl::init(false));

static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI);

MCSymbol *
WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
  const GlobalValue *Global = MO.getGlobal();
  if (!isa<Function>(Global)) {
    auto *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global));
    // If the symbol doesn't have an explicit WasmSymbolType yet and the
    // GlobalValue is actually a WebAssembly global, then ensure the symbol is a
    // WASM_SYMBOL_TYPE_GLOBAL.
    if (WebAssembly::isWasmVarAddressSpace(Global->getAddressSpace()) &&
        !WasmSym->getType()) {
      const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
      const TargetMachine &TM = MF.getTarget();
      const Function &CurrentFunc = MF.getFunction();
      Type *GlobalVT = Global->getValueType();
      SmallVector<MVT, 1> VTs;
      computeLegalValueVTs(CurrentFunc, TM, GlobalVT, VTs);

      // Tables are represented as Arrays in LLVM IR therefore
      // they reach this point as aggregate Array types with an element type
      // that is a reference type.
      wasm::ValType Type;
      bool IsTable = false;
      if (GlobalVT->isArrayTy() &&
          WebAssembly::isRefType(GlobalVT->getArrayElementType())) {
        MVT VT;
        IsTable = true;
        switch (GlobalVT->getArrayElementType()->getPointerAddressSpace()) {
        case WebAssembly::WasmAddressSpace::WASM_ADDRESS_SPACE_FUNCREF:
          VT = MVT::funcref;
          break;
        case WebAssembly::WasmAddressSpace::WASM_ADDRESS_SPACE_EXTERNREF:
          VT = MVT::externref;
          break;
        default:
          report_fatal_error("unhandled address space type");
        }
        Type = WebAssembly::toValType(VT);
      } else if (VTs.size() == 1) {
        Type = WebAssembly::toValType(VTs[0]);
      } else
        report_fatal_error("Aggregate globals not yet implemented");

      if (IsTable) {
        WasmSym->setType(wasm::WASM_SYMBOL_TYPE_TABLE);
        WasmSym->setTableType(Type);
      } else {
        WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
        WasmSym->setGlobalType(
            wasm::WasmGlobalType{uint8_t(Type), /*Mutable=*/true});
      }
    }
    return WasmSym;
  }

  const auto *FuncTy = cast<FunctionType>(Global->getValueType());
  const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
  const TargetMachine &TM = MF.getTarget();
  const Function &CurrentFunc = MF.getFunction();

  SmallVector<MVT, 1> ResultMVTs;
  SmallVector<MVT, 4> ParamMVTs;
  const auto *const F = dyn_cast<Function>(Global);
  computeSignatureVTs(FuncTy, F, CurrentFunc, TM, ParamMVTs, ResultMVTs);
  auto Signature = signatureFromMVTs(ResultMVTs, ParamMVTs);

  bool InvokeDetected = false;
  auto *WasmSym = Printer.getMCSymbolForFunction(
      F, WebAssembly::WasmEnableEmEH || WebAssembly::WasmEnableEmSjLj,
      Signature.get(), InvokeDetected);
  WasmSym->setSignature(Signature.get());
  Printer.addSignature(std::move(Signature));
  WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
  return WasmSym;
}

MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
    const MachineOperand &MO) const {
  return Printer.getOrCreateWasmSymbol(MO.getSymbolName());
}

MCOperand WebAssemblyMCInstLower::lowerSymbolOperand(const MachineOperand &MO,
                                                     MCSymbol *Sym) const {
  MCSymbolRefExpr::VariantKind Kind = MCSymbolRefExpr::VK_None;
  unsigned TargetFlags = MO.getTargetFlags();

  switch (TargetFlags) {
    case WebAssemblyII::MO_NO_FLAG:
      break;
    case WebAssemblyII::MO_GOT_TLS:
      Kind = MCSymbolRefExpr::VK_WASM_GOT_TLS;
      break;
    case WebAssemblyII::MO_GOT:
      Kind = MCSymbolRefExpr::VK_GOT;
      break;
    case WebAssemblyII::MO_MEMORY_BASE_REL:
      Kind = MCSymbolRefExpr::VK_WASM_MBREL;
      break;
    case WebAssemblyII::MO_TLS_BASE_REL:
      Kind = MCSymbolRefExpr::VK_WASM_TLSREL;
      break;
    case WebAssemblyII::MO_TABLE_BASE_REL:
      Kind = MCSymbolRefExpr::VK_WASM_TBREL;
      break;
    default:
      llvm_unreachable("Unknown target flag on GV operand");
  }

  const MCExpr *Expr = MCSymbolRefExpr::create(Sym, Kind, Ctx);

  if (MO.getOffset() != 0) {
    const auto *WasmSym = cast<MCSymbolWasm>(Sym);
    if (TargetFlags == WebAssemblyII::MO_GOT)
      report_fatal_error("GOT symbol references do not support offsets");
    if (WasmSym->isFunction())
      report_fatal_error("Function addresses with offsets not supported");
    if (WasmSym->isGlobal())
      report_fatal_error("Global indexes with offsets not supported");
    if (WasmSym->isTag())
      report_fatal_error("Tag indexes with offsets not supported");
    if (WasmSym->isTable())
      report_fatal_error("Table indexes with offsets not supported");

    Expr = MCBinaryExpr::createAdd(
        Expr, MCConstantExpr::create(MO.getOffset(), Ctx), Ctx);
  }

  return MCOperand::createExpr(Expr);
}

MCOperand WebAssemblyMCInstLower::lowerTypeIndexOperand(
    SmallVector<wasm::ValType, 1> &&Returns,
    SmallVector<wasm::ValType, 4> &&Params) const {
  auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns),
                                                         std::move(Params));
  MCSymbol *Sym = Printer.createTempSymbol("typeindex");
  auto *WasmSym = cast<MCSymbolWasm>(Sym);
  WasmSym->setSignature(Signature.get());
  Printer.addSignature(std::move(Signature));
  WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
  const MCExpr *Expr =
      MCSymbolRefExpr::create(WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx);
  return MCOperand::createExpr(Expr);
}

// Return the WebAssembly type associated with the given register class.
static wasm::ValType getType(const TargetRegisterClass *RC) {
  if (RC == &WebAssembly::I32RegClass)
    return wasm::ValType::I32;
  if (RC == &WebAssembly::I64RegClass)
    return wasm::ValType::I64;
  if (RC == &WebAssembly::F32RegClass)
    return wasm::ValType::F32;
  if (RC == &WebAssembly::F64RegClass)
    return wasm::ValType::F64;
  if (RC == &WebAssembly::V128RegClass)
    return wasm::ValType::V128;
  if (RC == &WebAssembly::EXTERNREFRegClass)
    return wasm::ValType::EXTERNREF;
  if (RC == &WebAssembly::FUNCREFRegClass)
    return wasm::ValType::FUNCREF;
  llvm_unreachable("Unexpected register class");
}

static void getFunctionReturns(const MachineInstr *MI,
                               SmallVectorImpl<wasm::ValType> &Returns) {
  const Function &F = MI->getMF()->getFunction();
  const TargetMachine &TM = MI->getMF()->getTarget();
  Type *RetTy = F.getReturnType();
  SmallVector<MVT, 4> CallerRetTys;
  computeLegalValueVTs(F, TM, RetTy, CallerRetTys);
  valTypesFromMVTs(CallerRetTys, Returns);
}

void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
                                   MCInst &OutMI) const {
  OutMI.setOpcode(MI->getOpcode());

  const MCInstrDesc &Desc = MI->getDesc();
  unsigned NumVariadicDefs = MI->getNumExplicitDefs() - Desc.getNumDefs();
  for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
    const MachineOperand &MO = MI->getOperand(I);

    MCOperand MCOp;
    switch (MO.getType()) {
    default:
      MI->print(errs());
      llvm_unreachable("unknown operand type");
    case MachineOperand::MO_MachineBasicBlock:
      MI->print(errs());
      llvm_unreachable("MachineBasicBlock operand should have been rewritten");
    case MachineOperand::MO_Register: {
      // Ignore all implicit register operands.
      if (MO.isImplicit())
        continue;
      const WebAssemblyFunctionInfo &MFI =
          *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
      unsigned WAReg = MFI.getWAReg(MO.getReg());
      MCOp = MCOperand::createReg(WAReg);
      break;
    }
    case MachineOperand::MO_Immediate: {
      unsigned DescIndex = I - NumVariadicDefs;
      if (DescIndex < Desc.NumOperands) {
        const MCOperandInfo &Info = Desc.OpInfo[DescIndex];
        if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
          SmallVector<wasm::ValType, 4> Returns;
          SmallVector<wasm::ValType, 4> Params;

          const MachineRegisterInfo &MRI =
              MI->getParent()->getParent()->getRegInfo();
          for (const MachineOperand &MO : MI->defs())
            Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
          for (const MachineOperand &MO : MI->explicit_uses())
            if (MO.isReg())
              Params.push_back(getType(MRI.getRegClass(MO.getReg())));

          // call_indirect instructions have a callee operand at the end which
          // doesn't count as a param.
          if (WebAssembly::isCallIndirect(MI->getOpcode()))
            Params.pop_back();

          // return_call_indirect instructions have the return type of the
          // caller
          if (MI->getOpcode() == WebAssembly::RET_CALL_INDIRECT)
            getFunctionReturns(MI, Returns);

          MCOp = lowerTypeIndexOperand(std::move(Returns), std::move(Params));
          break;
        } else if (Info.OperandType == WebAssembly::OPERAND_SIGNATURE) {
          auto BT = static_cast<WebAssembly::BlockType>(MO.getImm());
          assert(BT != WebAssembly::BlockType::Invalid);
          if (BT == WebAssembly::BlockType::Multivalue) {
            SmallVector<wasm::ValType, 1> Returns;
            getFunctionReturns(MI, Returns);
            MCOp = lowerTypeIndexOperand(std::move(Returns),
                                         SmallVector<wasm::ValType, 4>());
            break;
          }
        }
      }
      MCOp = MCOperand::createImm(MO.getImm());
      break;
    }
    case MachineOperand::MO_FPImmediate: {
      const ConstantFP *Imm = MO.getFPImm();
      const uint64_t BitPattern =
          Imm->getValueAPF().bitcastToAPInt().getZExtValue();
      if (Imm->getType()->isFloatTy())
        MCOp = MCOperand::createSFPImm(static_cast<uint32_t>(BitPattern));
      else if (Imm->getType()->isDoubleTy())
        MCOp = MCOperand::createDFPImm(BitPattern);
      else
        llvm_unreachable("unknown floating point immediate type");
      break;
    }
    case MachineOperand::MO_GlobalAddress:
      MCOp = lowerSymbolOperand(MO, GetGlobalAddressSymbol(MO));
      break;
    case MachineOperand::MO_ExternalSymbol:
      MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
      break;
    case MachineOperand::MO_MCSymbol:
      assert(MO.getTargetFlags() == 0 &&
             "WebAssembly does not use target flags on MCSymbol");
      MCOp = lowerSymbolOperand(MO, MO.getMCSymbol());
      break;
    }

    OutMI.addOperand(MCOp);
  }

  if (!WasmKeepRegisters)
    removeRegisterOperands(MI, OutMI);
  else if (Desc.variadicOpsAreDefs())
    OutMI.insert(OutMI.begin(), MCOperand::createImm(MI->getNumExplicitDefs()));
}

static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) {
  // Remove all uses of stackified registers to bring the instruction format
  // into its final stack form used thruout MC, and transition opcodes to
  // their _S variant.
  // We do this separate from the above code that still may need these
  // registers for e.g. call_indirect signatures.
  // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for
  // details.
  // TODO: the code above creates new registers which are then removed here.
  // That code could be slightly simplified by not doing that, though maybe
  // it is simpler conceptually to keep the code above in "register mode"
  // until this transition point.
  // FIXME: we are not processing inline assembly, which contains register
  // operands, because it is used by later target generic code.
  if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm())
    return;

  // Transform to _S instruction.
  auto RegOpcode = OutMI.getOpcode();
  auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode);
  assert(StackOpcode != -1 && "Failed to stackify instruction");
  OutMI.setOpcode(StackOpcode);

  // Remove register operands.
  for (auto I = OutMI.getNumOperands(); I; --I) {
    auto &MO = OutMI.getOperand(I - 1);
    if (MO.isReg()) {
      OutMI.erase(&MO);
    }
  }
}