lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp - llvm-project/llvm - Git at Google

 // 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/WebAssemblyMCTargetDesc.h"
 #include "TargetInfo/WebAssemblyTargetInfo.h"
 #include "WebAssemblyAsmPrinter.h"
 #include "WebAssemblyMachineFunctionInfo.h"
 #include "WebAssemblyRuntimeLibcallSignatures.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));

 extern cl::opt<bool> EnableEmException;
 extern cl::opt<bool> EnableEmSjLj;

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

 MCSymbol *
 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
   const GlobalValue *Global = MO.getGlobal();
   if (!isa<Function>(Global))
     return cast<MCSymbolWasm>(Printer.getSymbol(Global));

   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, EnableEmException || EnableEmSjLj, 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 {
   const char *Name = MO.getSymbolName();
   auto *WasmSym = cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
   const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();

   // Except for certain known symbols, all symbols used by CodeGen are
   // functions. It's OK to hardcode knowledge of specific symbols here; this
   // method is precisely there for fetching the signatures of known
   // Clang-provided symbols.
   if (strcmp(Name, "__stack_pointer") == 0 || strcmp(Name, "__tls_base") == 0 ||
       strcmp(Name, "__memory_base") == 0 || strcmp(Name, "__table_base") == 0 ||
       strcmp(Name, "__tls_size") == 0 || strcmp(Name, "__tls_align") == 0) {
     bool Mutable =
         strcmp(Name, "__stack_pointer") == 0 || strcmp(Name, "__tls_base") == 0;
     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
     WasmSym->setGlobalType(wasm::WasmGlobalType{
         uint8_t(Subtarget.hasAddr64() && strcmp(Name, "__table_base") != 0
                     ? wasm::WASM_TYPE_I64
                     : wasm::WASM_TYPE_I32),
         Mutable});
     return WasmSym;
   }

   SmallVector<wasm::ValType, 4> Returns;
   SmallVector<wasm::ValType, 4> Params;
   if (strcmp(Name, "__cpp_exception") == 0) {
     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
     // We can't confirm its signature index for now because there can be
     // imported exceptions. Set it to be 0 for now.
     WasmSym->setEventType(
         {wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
     // We may have multiple C++ compilation units to be linked together, each of
     // which defines the exception symbol. To resolve them, we declare them as
     // weak.
     WasmSym->setWeak(true);
     WasmSym->setExternal(true);

     // All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
     // (for wasm64) param type and void return type. The reaon is, all C++
     // exception values are pointers, and to share the type section with
     // functions, exceptions are assumed to have void return type.
     Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
                                            : wasm::ValType::I32);
   } else { // Function symbols
     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
     getLibcallSignature(Subtarget, Name, Returns, Params);
   }
   auto Signature =
       std::make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params));
   WasmSym->setSignature(Signature.get());
   Printer.addSignature(std::move(Signature));

   return WasmSym;
 }

 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:
       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->isEvent())
       report_fatal_error("Event 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;
   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;
           }
         } else if (Info.OperandType == WebAssembly::OPERAND_HEAPTYPE) {
           assert(static_cast<WebAssembly::HeapType>(MO.getImm()) !=
                  WebAssembly::HeapType::Invalid);
           // With typed function references, this will need a case for type
           // index operands.  Otherwise, fall through.
         }
       }
       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:
       // The target flag indicates whether this is a symbol for a
       // variable or a function.
       assert(MO.getTargetFlags() == 0 &&
              "WebAssembly uses only symbol flags on ExternalSymbols");
       MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
       break;
     case MachineOperand::MO_MCSymbol:
       // This is currently used only for LSDA symbols (GCC_except_table),
       // because global addresses or other external symbols are handled above.
       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);
     }
   }
 }
	// 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/WebAssemblyMCTargetDesc.h"
	#include "TargetInfo/WebAssemblyTargetInfo.h"
	#include "WebAssemblyAsmPrinter.h"
	#include "WebAssemblyMachineFunctionInfo.h"
	#include "WebAssemblyRuntimeLibcallSignatures.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));

	extern cl::opt<bool> EnableEmException;
	extern cl::opt<bool> EnableEmSjLj;

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

	MCSymbol *
	WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
	const GlobalValue *Global = MO.getGlobal();
	if (!isa<Function>(Global))
	return cast<MCSymbolWasm>(Printer.getSymbol(Global));

	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, EnableEmException \|\| EnableEmSjLj, 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 {
	const char *Name = MO.getSymbolName();
	auto *WasmSym = cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
	const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();

	// Except for certain known symbols, all symbols used by CodeGen are
	// functions. It's OK to hardcode knowledge of specific symbols here; this
	// method is precisely there for fetching the signatures of known
	// Clang-provided symbols.
	if (strcmp(Name, "__stack_pointer") == 0 \|\| strcmp(Name, "__tls_base") == 0 \|\|
	strcmp(Name, "__memory_base") == 0 \|\| strcmp(Name, "__table_base") == 0 \|\|
	strcmp(Name, "__tls_size") == 0 \|\| strcmp(Name, "__tls_align") == 0) {
	bool Mutable =
	strcmp(Name, "__stack_pointer") == 0 \|\| strcmp(Name, "__tls_base") == 0;
	WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
	WasmSym->setGlobalType(wasm::WasmGlobalType{
	uint8_t(Subtarget.hasAddr64() && strcmp(Name, "__table_base") != 0
	? wasm::WASM_TYPE_I64
	: wasm::WASM_TYPE_I32),
	Mutable});
	return WasmSym;
	}

	SmallVector<wasm::ValType, 4> Returns;
	SmallVector<wasm::ValType, 4> Params;
	if (strcmp(Name, "__cpp_exception") == 0) {
	WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
	// We can't confirm its signature index for now because there can be
	// imported exceptions. Set it to be 0 for now.
	WasmSym->setEventType(
	{wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
	// We may have multiple C++ compilation units to be linked together, each of
	// which defines the exception symbol. To resolve them, we declare them as
	// weak.
	WasmSym->setWeak(true);
	WasmSym->setExternal(true);

	// All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
	// (for wasm64) param type and void return type. The reaon is, all C++
	// exception values are pointers, and to share the type section with
	// functions, exceptions are assumed to have void return type.
	Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
	: wasm::ValType::I32);
	} else { // Function symbols
	WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
	getLibcallSignature(Subtarget, Name, Returns, Params);
	}
	auto Signature =
	std::make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params));
	WasmSym->setSignature(Signature.get());
	Printer.addSignature(std::move(Signature));

	return WasmSym;
	}

	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:
	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->isEvent())
	report_fatal_error("Event 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;
	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;
	}
	} else if (Info.OperandType == WebAssembly::OPERAND_HEAPTYPE) {
	assert(static_cast<WebAssembly::HeapType>(MO.getImm()) !=
	WebAssembly::HeapType::Invalid);
	// With typed function references, this will need a case for type
	// index operands. Otherwise, fall through.
	}
	}
	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:
	// The target flag indicates whether this is a symbol for a
	// variable or a function.
	assert(MO.getTargetFlags() == 0 &&
	"WebAssembly uses only symbol flags on ExternalSymbols");
	MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
	break;
	case MachineOperand::MO_MCSymbol:
	// This is currently used only for LSDA symbols (GCC_except_table),
	// because global addresses or other external symbols are handled above.
	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);
	}
	}
	}