llvm/tools/llvm-rc/ResourceScriptParser.cpp

//===-- ResourceScriptParser.cpp --------------------------------*- C++-*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//
//
// This implements the parser defined in ResourceScriptParser.h.
//
//===---------------------------------------------------------------------===//

#include "ResourceScriptParser.h"

// Take an expression returning llvm::Error and forward the error if it exists.
#define RETURN_IF_ERROR(Expr)                                                  \
  if (auto Err = (Expr))                                                       \
    return std::move(Err);

// Take an expression returning llvm::Expected<T> and assign it to Var or
// forward the error out of the function.
#define ASSIGN_OR_RETURN(Var, Expr)                                            \
  auto Var = (Expr);                                                           \
  if (!Var)                                                                    \
    return Var.takeError();

namespace llvm {
namespace rc {

RCParser::ParserError::ParserError(const Twine Expected, const LocIter CurLoc,
                                   const LocIter End)
    : ErrorLoc(CurLoc), FileEnd(End) {
  CurMessage = "Error parsing file: expected " + Expected.str() + ", got " +
               (CurLoc == End ? "<EOF>" : CurLoc->value()).str();
}

char RCParser::ParserError::ID = 0;

RCParser::RCParser(const std::vector<RCToken> &TokenList)
    : Tokens(TokenList), CurLoc(Tokens.begin()), End(Tokens.end()) {}

RCParser::RCParser(std::vector<RCToken> &&TokenList)
    : Tokens(std::move(TokenList)), CurLoc(Tokens.begin()), End(Tokens.end()) {}

bool RCParser::isEof() const { return CurLoc == End; }

RCParser::ParseType RCParser::parseSingleResource() {
  // The first thing we read is usually a resource's name. However, in some
  // cases (LANGUAGE and STRINGTABLE) the resources don't have their names
  // and the first token to be read is the type.
  ASSIGN_OR_RETURN(NameToken, readTypeOrName());

  if (NameToken->equalsLower("LANGUAGE"))
    return parseLanguageResource();
  else if (NameToken->equalsLower("STRINGTABLE"))
    return parseStringTableResource();

  // If it's not an unnamed resource, what we've just read is a name. Now,
  // read resource type;
  ASSIGN_OR_RETURN(TypeToken, readTypeOrName());

  ParseType Result = std::unique_ptr<RCResource>();
  (void)!Result;

  if (TypeToken->equalsLower("ACCELERATORS"))
    Result = parseAcceleratorsResource();
  else if (TypeToken->equalsLower("CURSOR"))
    Result = parseCursorResource();
  else if (TypeToken->equalsLower("DIALOG"))
    Result = parseDialogResource(false);
  else if (TypeToken->equalsLower("DIALOGEX"))
    Result = parseDialogResource(true);
  else if (TypeToken->equalsLower("ICON"))
    Result = parseIconResource();
  else if (TypeToken->equalsLower("HTML"))
    Result = parseHTMLResource();
  else if (TypeToken->equalsLower("MENU"))
    Result = parseMenuResource();
  else if (TypeToken->equalsLower("VERSIONINFO"))
    Result = parseVersionInfoResource();
  else
    Result = parseUserDefinedResource(*TypeToken);

  if (Result)
    (*Result)->setName(*NameToken);

  return Result;
}

bool RCParser::isNextTokenKind(Kind TokenKind) const {
  return !isEof() && look().kind() == TokenKind;
}

const RCToken &RCParser::look() const {
  assert(!isEof());
  return *CurLoc;
}

const RCToken &RCParser::read() {
  assert(!isEof());
  return *CurLoc++;
}

void RCParser::consume() {
  assert(!isEof());
  CurLoc++;
}

// An integer description might consist of a single integer or
// an arithmetic expression evaluating to the integer. The expressions
// can contain the following tokens: <int> ( ) + - | & ~. Their meaning
// is the same as in C++.
// The operators in the original RC implementation have the following
// precedence:
//   1) Unary operators (- ~),
//   2) Binary operators (+ - & |), with no precedence.
//
// The following grammar is used to parse the expressions Exp1:
//   Exp1 ::= Exp2 || Exp1 + Exp2 || Exp1 - Exp2 || Exp1 | Exp2 || Exp1 & Exp2
//   Exp2 ::= -Exp2 || ~Exp2 || Int || (Exp1).
// (More conveniently, Exp1 is a non-empty sequence of Exp2 expressions,
// separated by binary operators.)
//
// Expressions of type Exp1 are read by parseIntExpr1(Inner) method, while Exp2
// is read by parseIntExpr2().
//
// The original Microsoft tool handles multiple unary operators incorrectly.
// For example, in 16-bit little-endian integers:
//    1 => 01 00, -1 => ff ff, --1 => ff ff, ---1 => 01 00;
//    1 => 01 00, ~1 => fe ff, ~~1 => fd ff, ~~~1 => fc ff.
// Our implementation differs from the original one and handles these
// operators correctly:
//    1 => 01 00, -1 => ff ff, --1 => 01 00, ---1 => ff ff;
//    1 => 01 00, ~1 => fe ff, ~~1 => 01 00, ~~~1 => fe ff.

Expected<uint32_t> RCParser::readInt() { return parseIntExpr1(); }

Expected<uint32_t> RCParser::parseIntExpr1() {
  // Exp1 ::= Exp2 || Exp1 + Exp2 || Exp1 - Exp2 || Exp1 | Exp2 || Exp1 & Exp2.
  ASSIGN_OR_RETURN(FirstResult, parseIntExpr2());
  uint32_t Result = *FirstResult;

  while (!isEof() && look().isBinaryOp()) {
    auto OpToken = read();
    ASSIGN_OR_RETURN(NextResult, parseIntExpr2());

    switch (OpToken.kind()) {
    case Kind::Plus:
      Result += *NextResult;
      break;

    case Kind::Minus:
      Result -= *NextResult;
      break;

    case Kind::Pipe:
      Result |= *NextResult;
      break;

    case Kind::Amp:
      Result &= *NextResult;
      break;

    default:
      llvm_unreachable("Already processed all binary ops.");
    }
  }

  return Result;
}

Expected<uint32_t> RCParser::parseIntExpr2() {
  // Exp2 ::= -Exp2 || ~Exp2 || Int || (Exp1).
  static const char ErrorMsg[] = "'-', '~', integer or '('";

  if (isEof())
    return getExpectedError(ErrorMsg);

  switch (look().kind()) {
  case Kind::Minus: {
    consume();
    ASSIGN_OR_RETURN(Result, parseIntExpr2());
    return -(*Result);
  }

  case Kind::Tilde: {
    consume();
    ASSIGN_OR_RETURN(Result, parseIntExpr2());
    return ~(*Result);
  }

  case Kind::Int:
    return read().intValue();

  case Kind::LeftParen: {
    consume();
    ASSIGN_OR_RETURN(Result, parseIntExpr1());
    RETURN_IF_ERROR(consumeType(Kind::RightParen));
    return *Result;
  }

  default:
    return getExpectedError(ErrorMsg);
  }
}

Expected<StringRef> RCParser::readString() {
  if (!isNextTokenKind(Kind::String))
    return getExpectedError("string");
  return read().value();
}

Expected<StringRef> RCParser::readIdentifier() {
  if (!isNextTokenKind(Kind::Identifier))
    return getExpectedError("identifier");
  return read().value();
}

Expected<IntOrString> RCParser::readIntOrString() {
  if (!isNextTokenKind(Kind::Int) && !isNextTokenKind(Kind::String))
    return getExpectedError("int or string");
  return IntOrString(read());
}

Expected<IntOrString> RCParser::readTypeOrName() {
  // We suggest that the correct resource name or type should be either an
  // identifier or an integer. The original RC tool is much more liberal.
  if (!isNextTokenKind(Kind::Identifier) && !isNextTokenKind(Kind::Int))
    return getExpectedError("int or identifier");
  return IntOrString(read());
}

Error RCParser::consumeType(Kind TokenKind) {
  if (isNextTokenKind(TokenKind)) {
    consume();
    return Error::success();
  }

  switch (TokenKind) {
#define TOKEN(TokenName)                                                       \
  case Kind::TokenName:                                                        \
    return getExpectedError(#TokenName);
#define SHORT_TOKEN(TokenName, TokenCh)                                        \
  case Kind::TokenName:                                                        \
    return getExpectedError(#TokenCh);
#include "ResourceScriptTokenList.h"
#undef SHORT_TOKEN
#undef TOKEN
  }

  llvm_unreachable("All case options exhausted.");
}

bool RCParser::consumeOptionalType(Kind TokenKind) {
  if (isNextTokenKind(TokenKind)) {
    consume();
    return true;
  }

  return false;
}

Expected<SmallVector<uint32_t, 8>>
RCParser::readIntsWithCommas(size_t MinCount, size_t MaxCount) {
  assert(MinCount <= MaxCount);

  SmallVector<uint32_t, 8> Result;

  auto FailureHandler =
      [&](llvm::Error Err) -> Expected<SmallVector<uint32_t, 8>> {
    if (Result.size() < MinCount)
      return std::move(Err);
    consumeError(std::move(Err));
    return Result;
  };

  for (size_t i = 0; i < MaxCount; ++i) {
    // Try to read a comma unless we read the first token.
    // Sometimes RC tool requires them and sometimes not. We decide to
    // always require them.
    if (i >= 1) {
      if (auto CommaError = consumeType(Kind::Comma))
        return FailureHandler(std::move(CommaError));
    }

    if (auto IntResult = readInt())
      Result.push_back(*IntResult);
    else
      return FailureHandler(IntResult.takeError());
  }

  return std::move(Result);
}

Expected<uint32_t> RCParser::parseFlags(ArrayRef<StringRef> FlagDesc) {
  assert(FlagDesc.size() <= 32 && "More than 32 flags won't fit in result.");
  assert(!FlagDesc.empty());

  uint32_t Result = 0;
  while (isNextTokenKind(Kind::Comma)) {
    consume();
    ASSIGN_OR_RETURN(FlagResult, readIdentifier());
    bool FoundFlag = false;

    for (size_t FlagId = 0; FlagId < FlagDesc.size(); ++FlagId) {
      if (!FlagResult->equals_lower(FlagDesc[FlagId]))
        continue;

      Result |= (1U << FlagId);
      FoundFlag = true;
      break;
    }

    if (!FoundFlag)
      return getExpectedError(join(FlagDesc, "/"), true);
  }

  return Result;
}

// As for now, we ignore the extended set of statements.
Expected<OptionalStmtList> RCParser::parseOptionalStatements(bool IsExtended) {
  OptionalStmtList Result;

  // The last statement is always followed by the start of the block.
  while (!isNextTokenKind(Kind::BlockBegin)) {
    ASSIGN_OR_RETURN(SingleParse, parseSingleOptionalStatement(IsExtended));
    Result.addStmt(std::move(*SingleParse));
  }

  return std::move(Result);
}

Expected<std::unique_ptr<OptionalStmt>>
RCParser::parseSingleOptionalStatement(bool IsExtended) {
  ASSIGN_OR_RETURN(TypeToken, readIdentifier());
  if (TypeToken->equals_lower("CHARACTERISTICS"))
    return parseCharacteristicsStmt();
  if (TypeToken->equals_lower("LANGUAGE"))
    return parseLanguageStmt();
  if (TypeToken->equals_lower("VERSION"))
    return parseVersionStmt();

  if (IsExtended) {
    if (TypeToken->equals_lower("CAPTION"))
      return parseCaptionStmt();
    if (TypeToken->equals_lower("FONT"))
      return parseFontStmt();
    if (TypeToken->equals_lower("STYLE"))
      return parseStyleStmt();
  }

  return getExpectedError("optional statement type, BEGIN or '{'",
                          /* IsAlreadyRead = */ true);
}

RCParser::ParseType RCParser::parseLanguageResource() {
  // Read LANGUAGE as an optional statement. If it's read correctly, we can
  // upcast it to RCResource.
  return parseLanguageStmt();
}

RCParser::ParseType RCParser::parseAcceleratorsResource() {
  ASSIGN_OR_RETURN(OptStatements, parseOptionalStatements());
  RETURN_IF_ERROR(consumeType(Kind::BlockBegin));

  auto Accels = make_unique<AcceleratorsResource>(std::move(*OptStatements));

  while (!consumeOptionalType(Kind::BlockEnd)) {
    ASSIGN_OR_RETURN(EventResult, readIntOrString());
    RETURN_IF_ERROR(consumeType(Kind::Comma));
    ASSIGN_OR_RETURN(IDResult, readInt());
    ASSIGN_OR_RETURN(FlagsResult,
                     parseFlags(AcceleratorsResource::Accelerator::OptionsStr));
    Accels->addAccelerator(*EventResult, *IDResult, *FlagsResult);
  }

  return std::move(Accels);
}

RCParser::ParseType RCParser::parseCursorResource() {
  ASSIGN_OR_RETURN(Arg, readString());
  return make_unique<CursorResource>(*Arg);
}

RCParser::ParseType RCParser::parseDialogResource(bool IsExtended) {
  // Dialog resources have the following format of the arguments:
  //  DIALOG:   x, y, width, height [opt stmts...] {controls...}
  //  DIALOGEX: x, y, width, height [, helpID] [opt stmts...] {controls...}
  // These are very similar, so we parse them together.
  ASSIGN_OR_RETURN(LocResult, readIntsWithCommas(4, 4));

  uint32_t HelpID = 0; // When HelpID is unset, it's assumed to be 0.
  if (IsExtended && consumeOptionalType(Kind::Comma)) {
    ASSIGN_OR_RETURN(HelpIDResult, readInt());
    HelpID = *HelpIDResult;
  }

  ASSIGN_OR_RETURN(OptStatements,
                   parseOptionalStatements(/*UseExtendedStmts = */ true));

  assert(isNextTokenKind(Kind::BlockBegin) &&
         "parseOptionalStatements, when successful, halts on BlockBegin.");
  consume();

  auto Dialog = make_unique<DialogResource>(
      (*LocResult)[0], (*LocResult)[1], (*LocResult)[2], (*LocResult)[3],
      HelpID, std::move(*OptStatements), IsExtended);

  while (!consumeOptionalType(Kind::BlockEnd)) {
    ASSIGN_OR_RETURN(ControlDefResult, parseControl());
    Dialog->addControl(std::move(*ControlDefResult));
  }

  return std::move(Dialog);
}

RCParser::ParseType RCParser::parseUserDefinedResource(IntOrString Type) {
  if (isEof())
    return getExpectedError("filename, '{' or BEGIN");

  // Check if this is a file resource.
  if (look().kind() == Kind::String)
    return make_unique<UserDefinedResource>(Type, read().value());

  RETURN_IF_ERROR(consumeType(Kind::BlockBegin));
  std::vector<IntOrString> Data;

  // Consume comma before each consecutive token except the first one.
  bool ConsumeComma = false;
  while (!consumeOptionalType(Kind::BlockEnd)) {
    if (ConsumeComma)
      RETURN_IF_ERROR(consumeType(Kind::Comma));
    ConsumeComma = true;

    ASSIGN_OR_RETURN(Item, readIntOrString());
    Data.push_back(*Item);
  }

  return make_unique<UserDefinedResource>(Type, std::move(Data));
}

RCParser::ParseType RCParser::parseVersionInfoResource() {
  ASSIGN_OR_RETURN(FixedResult, parseVersionInfoFixed());
  ASSIGN_OR_RETURN(BlockResult, parseVersionInfoBlockContents(StringRef()));
  return llvm::make_unique<VersionInfoResource>(std::move(**BlockResult),
                                                std::move(*FixedResult));
}

Expected<Control> RCParser::parseControl() {
  // Each control definition (except CONTROL) follows one of the schemes below
  // depending on the control class:
  //  [class] text, id, x, y, width, height [, style] [, exstyle] [, helpID]
  //  [class]       id, x, y, width, height [, style] [, exstyle] [, helpID]
  // Note that control ids must be integers.
  ASSIGN_OR_RETURN(ClassResult, readIdentifier());
  std::string ClassUpper = ClassResult->upper();
  if (Control::SupportedCtls.find(ClassUpper) == Control::SupportedCtls.end())
    return getExpectedError("control type, END or '}'", true);

  // Read caption if necessary.
  StringRef Caption;
  if (Control::CtlsWithTitle.find(ClassUpper) != Control::CtlsWithTitle.end()) {
    ASSIGN_OR_RETURN(CaptionResult, readString());
    RETURN_IF_ERROR(consumeType(Kind::Comma));
    Caption = *CaptionResult;
  }

  ASSIGN_OR_RETURN(Args, readIntsWithCommas(5, 8));

  auto TakeOptArg = [&Args](size_t Id) -> Optional<uint32_t> {
    return Args->size() > Id ? (*Args)[Id] : Optional<uint32_t>();
  };

  return Control(*ClassResult, Caption, (*Args)[0], (*Args)[1], (*Args)[2],
                 (*Args)[3], (*Args)[4], TakeOptArg(5), TakeOptArg(6),
                 TakeOptArg(7));
}

RCParser::ParseType RCParser::parseIconResource() {
  ASSIGN_OR_RETURN(Arg, readString());
  return make_unique<IconResource>(*Arg);
}

RCParser::ParseType RCParser::parseHTMLResource() {
  ASSIGN_OR_RETURN(Arg, readString());
  return make_unique<HTMLResource>(*Arg);
}

RCParser::ParseType RCParser::parseMenuResource() {
  ASSIGN_OR_RETURN(OptStatements, parseOptionalStatements());
  ASSIGN_OR_RETURN(Items, parseMenuItemsList());
  return make_unique<MenuResource>(std::move(*OptStatements),
                                   std::move(*Items));
}

Expected<MenuDefinitionList> RCParser::parseMenuItemsList() {
  RETURN_IF_ERROR(consumeType(Kind::BlockBegin));

  MenuDefinitionList List;

  // Read a set of items. Each item is of one of three kinds:
  //   MENUITEM SEPARATOR
  //   MENUITEM caption:String, result:Int [, menu flags]...
  //   POPUP caption:String [, menu flags]... { items... }
  while (!consumeOptionalType(Kind::BlockEnd)) {
    ASSIGN_OR_RETURN(ItemTypeResult, readIdentifier());

    bool IsMenuItem = ItemTypeResult->equals_lower("MENUITEM");
    bool IsPopup = ItemTypeResult->equals_lower("POPUP");
    if (!IsMenuItem && !IsPopup)
      return getExpectedError("MENUITEM, POPUP, END or '}'", true);

    if (IsMenuItem && isNextTokenKind(Kind::Identifier)) {
      // Now, expecting SEPARATOR.
      ASSIGN_OR_RETURN(SeparatorResult, readIdentifier());
      if (SeparatorResult->equals_lower("SEPARATOR")) {
        List.addDefinition(make_unique<MenuSeparator>());
        continue;
      }

      return getExpectedError("SEPARATOR or string", true);
    }

    // Not a separator. Read the caption.
    ASSIGN_OR_RETURN(CaptionResult, readString());

    // If MENUITEM, expect also a comma and an integer.
    uint32_t MenuResult = -1;

    if (IsMenuItem) {
      RETURN_IF_ERROR(consumeType(Kind::Comma));
      ASSIGN_OR_RETURN(IntResult, readInt());
      MenuResult = *IntResult;
    }

    ASSIGN_OR_RETURN(FlagsResult, parseFlags(MenuDefinition::OptionsStr));

    if (IsPopup) {
      // If POPUP, read submenu items recursively.
      ASSIGN_OR_RETURN(SubMenuResult, parseMenuItemsList());
      List.addDefinition(make_unique<PopupItem>(*CaptionResult, *FlagsResult,
                                                std::move(*SubMenuResult)));
      continue;
    }

    assert(IsMenuItem);
    List.addDefinition(
        make_unique<MenuItem>(*CaptionResult, MenuResult, *FlagsResult));
  }

  return std::move(List);
}

RCParser::ParseType RCParser::parseStringTableResource() {
  ASSIGN_OR_RETURN(OptStatements, parseOptionalStatements());
  RETURN_IF_ERROR(consumeType(Kind::BlockBegin));

  auto Table = make_unique<StringTableResource>(std::move(*OptStatements));

  // Read strings until we reach the end of the block.
  while (!consumeOptionalType(Kind::BlockEnd)) {
    // Each definition consists of string's ID (an integer) and a string.
    // Some examples in documentation suggest that there might be a comma in
    // between, however we strictly adhere to the single statement definition.
    ASSIGN_OR_RETURN(IDResult, readInt());
    ASSIGN_OR_RETURN(StrResult, readString());
    Table->addString(*IDResult, *StrResult);
  }

  return std::move(Table);
}

Expected<std::unique_ptr<VersionInfoBlock>>
RCParser::parseVersionInfoBlockContents(StringRef BlockName) {
  RETURN_IF_ERROR(consumeType(Kind::BlockBegin));

  auto Contents = llvm::make_unique<VersionInfoBlock>(BlockName);

  while (!isNextTokenKind(Kind::BlockEnd)) {
    ASSIGN_OR_RETURN(Stmt, parseVersionInfoStmt());
    Contents->addStmt(std::move(*Stmt));
  }

  consume(); // Consume BlockEnd.

  return std::move(Contents);
}

Expected<std::unique_ptr<VersionInfoStmt>> RCParser::parseVersionInfoStmt() {
  // Expect either BLOCK or VALUE, then a name or a key (a string).
  ASSIGN_OR_RETURN(TypeResult, readIdentifier());

  if (TypeResult->equals_lower("BLOCK")) {
    ASSIGN_OR_RETURN(NameResult, readString());
    return parseVersionInfoBlockContents(*NameResult);
  }

  if (TypeResult->equals_lower("VALUE")) {
    ASSIGN_OR_RETURN(KeyResult, readString());
    // Read a (possibly empty) list of strings and/or ints, each preceded by
    // a comma.
    std::vector<IntOrString> Values;

    while (consumeOptionalType(Kind::Comma)) {
      ASSIGN_OR_RETURN(ValueResult, readIntOrString());
      Values.push_back(*ValueResult);
    }
    return llvm::make_unique<VersionInfoValue>(*KeyResult, std::move(Values));
  }

  return getExpectedError("BLOCK or VALUE", true);
}

Expected<VersionInfoResource::VersionInfoFixed>
RCParser::parseVersionInfoFixed() {
  using RetType = VersionInfoResource::VersionInfoFixed;
  RetType Result;

  // Read until the beginning of the block.
  while (!isNextTokenKind(Kind::BlockBegin)) {
    ASSIGN_OR_RETURN(TypeResult, readIdentifier());
    auto FixedType = RetType::getFixedType(*TypeResult);

    if (!RetType::isTypeSupported(FixedType))
      return getExpectedError("fixed VERSIONINFO statement type", true);
    if (Result.IsTypePresent[FixedType])
      return getExpectedError("yet unread fixed VERSIONINFO statement type",
                              true);

    // VERSION variations take multiple integers.
    size_t NumInts = RetType::isVersionType(FixedType) ? 4 : 1;
    ASSIGN_OR_RETURN(ArgsResult, readIntsWithCommas(NumInts, NumInts));
    Result.setValue(FixedType, *ArgsResult);
  }

  return Result;
}

RCParser::ParseOptionType RCParser::parseLanguageStmt() {
  ASSIGN_OR_RETURN(Args, readIntsWithCommas(/* min = */ 2, /* max = */ 2));
  return make_unique<LanguageResource>((*Args)[0], (*Args)[1]);
}

RCParser::ParseOptionType RCParser::parseCharacteristicsStmt() {
  ASSIGN_OR_RETURN(Arg, readInt());
  return make_unique<CharacteristicsStmt>(*Arg);
}

RCParser::ParseOptionType RCParser::parseVersionStmt() {
  ASSIGN_OR_RETURN(Arg, readInt());
  return make_unique<VersionStmt>(*Arg);
}

RCParser::ParseOptionType RCParser::parseCaptionStmt() {
  ASSIGN_OR_RETURN(Arg, readString());
  return make_unique<CaptionStmt>(*Arg);
}

RCParser::ParseOptionType RCParser::parseFontStmt() {
  ASSIGN_OR_RETURN(SizeResult, readInt());
  RETURN_IF_ERROR(consumeType(Kind::Comma));
  ASSIGN_OR_RETURN(NameResult, readString());
  return make_unique<FontStmt>(*SizeResult, *NameResult);
}

RCParser::ParseOptionType RCParser::parseStyleStmt() {
  ASSIGN_OR_RETURN(Arg, readInt());
  return make_unique<StyleStmt>(*Arg);
}

Error RCParser::getExpectedError(const Twine Message, bool IsAlreadyRead) {
  return make_error<ParserError>(
      Message, IsAlreadyRead ? std::prev(CurLoc) : CurLoc, End);
}

} // namespace rc
} // namespace llvm