WebAssemblyMCInstLower.cpp

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// 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 "MCTargetDesc/WebAssemblyMCAsmInfo.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "MCTargetDesc/WebAssemblyMCTypeUtilities.h"
#include "TargetInfo/WebAssemblyTargetInfo.h"
#include "Utils/WebAssemblyTypeUtilities.h"
#include "WebAssemblyAsmPrinter.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblyUtilities.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/GlobalVariable.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"
#include <optional>
 
using namespace llvm;
 
// This disables the removal of registers when lowering into MC, as required
// by some current tests.
static 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 std::optional<bool> getWasmGlobalMutable(const GlobalValue *Global,
                                                const Function &CurrentFunc,
                                                const DiagnosticLocation &DL) {
  const auto *BaseObject = Global->getAliaseeObject();
  const auto *GV = dyn_cast_or_null<GlobalVariable>(BaseObject);
  if (!GV) {
    CurrentFunc.getContext().diagnose(DiagnosticInfoUnsupported(
        CurrentFunc,
        "wasm_var address space symbol must resolve to a "
        "GlobalVariable",
        DL));
    return std::nullopt;
  }
  return !GV->isConstant();
}
 
static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI);
 
MCSymbol *
WebAssemblyMCInstLower::GetGlobalAddressSymbol(const GlobalValue &Global,
                                               const DebugLoc &DL) const {
  const TargetMachine &TM = Printer.TM;
  const Function &CurrentFunc = Printer.MF->getFunction();
  if (!isa<Function>(Global)) {
    auto *WasmSym = static_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()) {
      std::optional<bool> Mutable =
          getWasmGlobalMutable(&Global, CurrentFunc, DL);
      if (!Mutable.has_value())
        return WasmSym;
 
      Type *GlobalVT = Global.getValueType();
      SmallVector<MVT, 1> VTs;
      computeLegalValueVTs(CurrentFunc, TM, GlobalVT, VTs);
 
      WebAssembly::wasmSymbolSetType(WasmSym, GlobalVT, VTs, *Mutable);
    }
    return WasmSym;
  }
 
  const auto *FuncTy = cast<FunctionType>(Global.getValueType());
 
  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(Ctx, ResultMVTs, ParamMVTs);
 
  bool InvokeDetected = false;
  auto *WasmSym = Printer.getMCSymbolForFunction(F, Signature, InvokeDetected);
  WasmSym->setSignature(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 {
  auto Spec = WebAssembly::S_None;
  unsigned TargetFlags = MO.getTargetFlags();
 
  switch (TargetFlags) {
    case WebAssemblyII::MO_NO_FLAG:
      break;
    case WebAssemblyII::MO_GOT_TLS:
      Spec = WebAssembly::S_GOT_TLS;
      break;
    case WebAssemblyII::MO_GOT:
      Spec = WebAssembly::S_GOT;
      break;
    case WebAssemblyII::MO_MEMORY_BASE_REL:
      Spec = WebAssembly::S_MBREL;
      break;
    case WebAssemblyII::MO_TLS_BASE_REL:
      Spec = WebAssembly::S_TLSREL;
      break;
    case WebAssemblyII::MO_TABLE_BASE_REL:
      Spec = WebAssembly::S_TBREL;
      break;
    default:
      llvm_unreachable("Unknown target flag on GV operand");
  }
 
  const MCExpr *Expr = MCSymbolRefExpr::create(Sym, Spec, Ctx);
 
  if (MO.getOffset() != 0) {
    const auto *WasmSym = static_cast<const 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(
    SmallVectorImpl<wasm::ValType> &&Returns,
    SmallVectorImpl<wasm::ValType> &&Params) const {
  auto Signature = Ctx.createWasmSignature();
  Signature->Returns = std::move(Returns);
  Signature->Params = std::move(Params);
  auto *Sym =
      static_cast<MCSymbolWasm *>(Printer.createTempSymbol("typeindex"));
  Sym->setSignature(Signature);
  Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
  const MCExpr *Expr =
      MCSymbolRefExpr::create(Sym, WebAssembly::S_TYPEINDEX, Ctx);
  return MCOperand::createExpr(Expr);
}
 
MCOperand
WebAssemblyMCInstLower::lowerEncodedFunctionSignature(const APInt &Sig) const {
  // For APInt a word is 64 bits on all architectures, see definition in APInt.h
  auto NumWords = Sig.getNumWords();
  SmallVector<wasm::ValType, 4> Params;
  SmallVector<wasm::ValType, 2> Returns;
 
  int Idx = NumWords;
  auto GetWord = [&Idx, &Sig]() {
    Idx--;
    return Sig.extractBitsAsZExtValue(64, 64 * Idx);
  };
  // Annoying special case: if getSignificantBits() <= 64 then InstrEmitter will
  // emit an Imm instead of a CImm. It simplifies WebAssemblyMCInstLower if we
  // always emit a CImm. So xor NParams with 0x7ffffff to ensure
  // getSignificantBits() > 64
  // See encodeFunctionSignature in WebAssemblyISelDAGtoDAG.cpp
  int NReturns = GetWord() ^ 0x7ffffff;
  for (int I = 0; I < NReturns; I++) {
    Returns.push_back(static_cast<wasm::ValType>(GetWord()));
  }
  int NParams = GetWord();
  for (int I = 0; I < NParams; I++) {
    Params.push_back(static_cast<wasm::ValType>(GetWord()));
  }
  return lowerTypeIndexOperand(std::move(Returns), std::move(Params));
}
 
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();
  const MachineFunction *MF = MI->getMF();
  const auto &TLI =
      *MF->getSubtarget<WebAssemblySubtarget>().getTargetLowering();
  wasm::ValType PtrTy = TLI.getPointerTy(MF->getDataLayout()) == MVT::i32
                            ? wasm::ValType::I32
                            : wasm::ValType::I64;
 
  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 llvm::MachineOperand::MO_CImmediate: {
      // Lower type index placeholder for ref.test
      // Currently this is the only way that CImmediates show up so panic if we
      // get confused.
      unsigned DescIndex = I - NumVariadicDefs;
      assert(DescIndex < Desc.NumOperands && "unexpected CImmediate operand");
      auto Operands = Desc.operands();
      const MCOperandInfo &Info = Operands[DescIndex];
      assert(Info.OperandType == WebAssembly::OPERAND_TYPEINDEX &&
             "unexpected CImmediate operand");
      (void)Info;
      MCOp = lowerEncodedFunctionSignature(MO.getCImm()->getValue());
      break;
    }
    case MachineOperand::MO_Immediate: {
      unsigned DescIndex = I - NumVariadicDefs;
      if (DescIndex < Desc.NumOperands) {
        auto Operands = Desc.operands();
        const MCOperandInfo &Info = Operands[DescIndex];
        // Replace type index placeholder with actual type index. The type index
        // placeholders are Immediates and have an operand type of
        // OPERAND_TYPEINDEX or OPERAND_SIGNATURE.
        if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
          // Lower type index placeholder for a CALL_INDIRECT instruction
          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(WebAssembly::regClassToValType(
                MRI.getRegClass(MO.getReg())->getID()));
          for (const MachineOperand &MO : MI->explicit_uses())
            if (MO.isReg())
              Params.push_back(WebAssembly::regClassToValType(
                  MRI.getRegClass(MO.getReg())->getID()));
 
          // 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;
        }
        if (Info.OperandType == WebAssembly::OPERAND_SIGNATURE) {
          // Lower type index placeholder for blocks
          auto BT = static_cast<WebAssembly::BlockType>(MO.getImm());
          assert(BT != WebAssembly::BlockType::Invalid);
          if (BT == WebAssembly::BlockType::Multivalue) {
            SmallVector<wasm::ValType, 2> Returns;
            // Multivalue blocks are emitted in two cases:
            // 1. When the blocks will never be exited and are at the ends of
            //    functions (see
            //    WebAssemblyCFGStackify::fixEndsAtEndOfFunction). In this case
            //    the exact multivalue signature can always be inferred from the
            //    return type of the parent function.
            // 2. (catch_ref ...) clause in try_table instruction. Currently all
            //    tags we support (cpp_exception and c_longjmp) throws a single
            //    pointer, so the multivalue signature for this case will be
            //    (ptr, exnref). Having MO_CATCH_BLOCK_SIG target flags means
            //    this is a destination of a catch_ref.
            if (MO.getTargetFlags() == WebAssemblyII::MO_CATCH_BLOCK_SIG) {
              Returns = {PtrTy, wasm::ValType::EXNREF};
            } else
              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.getGlobal(), MI->getDebugLoc()));
      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 throughout 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);
    }
  }
}