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llvm-project/llvm/lib/Target/WebAssembly/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 "WebAssemblyAsmPrinter.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblyRuntimeLibcallSignatures.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.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;
// Defines llvm::WebAssembly::getStackOpcode to convert register instructions to
// stack instructions
#define GET_INSTRMAP_INFO 1
#include "WebAssemblyGenInstrInfo.inc"
// 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();
auto *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global));
if (const auto *FuncTy = dyn_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;
computeSignatureVTs(FuncTy, CurrentFunc, TM, ParamMVTs, ResultMVTs);
auto Signature = signatureFromMVTs(ResultMVTs, ParamMVTs);
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() ? 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_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");
Expr = MCBinaryExpr::createAdd(
Expr, MCConstantExpr::create(MO.getOffset(), Ctx), 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");
}
void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
MCInst &OutMI) const {
OutMI.setOpcode(MI->getOpcode());
const MCInstrDesc &Desc = MI->getDesc();
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:
if (I < Desc.NumOperands) {
const MCOperandInfo &Info = Desc.OpInfo[I];
if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
MCSymbol *Sym = Printer.createTempSymbol("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) {
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);
}
auto *WasmSym = cast<MCSymbolWasm>(Sym);
auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns),
std::move(Params));
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);
MCOp = MCOperand::createExpr(Expr);
break;
}
}
MCOp = MCOperand::createImm(MO.getImm());
break;
case MachineOperand::MO_FPImmediate: {
// TODO: MC converts all floating point immediate operands to double.
// This is fine for numeric values, but may cause NaNs to change bits.
const ConstantFP *Imm = MO.getFPImm();
if (Imm->getType()->isFloatTy())
MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
else if (Imm->getType()->isDoubleTy())
MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
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);
}
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 seperate 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);
}
}
}
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