text: //===- Main.cpp - Top-Level TableGen implementation -----------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // TableGen is a tool which can be used to build up a description of something,
  // then invoke one or more "tablegen backends" to emit information about the
  // description in some predefined format.  In practice, this is used by the LLVM
  // code generators to automate generation of a code generator through a
  // high-level description of the target.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/TableGen/Main.h"
  #include "TGParser.h"
  #include "llvm/ADT/StringExtras.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/FileSystem.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/ToolOutputFile.h"
  #include "llvm/TableGen/Error.h"
  #include "llvm/TableGen/Record.h"
  #include <algorithm>
  #include <cstdio>
  #include <system_error>
  using namespace llvm;
  
  static cl::opt<std::string>
  OutputFilename("o", cl::desc("Output filename"), cl::value_desc("filename"),
                 cl::init("-"));
  
  static cl::opt<std::string>
  DependFilename("d",
                 cl::desc("Dependency filename"),
                 cl::value_desc("filename"),
                 cl::init(""));
  
  static cl::opt<std::string>
  InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-"));
  
  static cl::list<std::string>
  IncludeDirs("I", cl::desc("Directory of include files"),
              cl::value_desc("directory"), cl::Prefix);
  
  static int reportError(const char *ProgName, Twine Msg) {
    errs() << ProgName << ": " << Msg;
    errs().flush();
    return 1;
  }
  
  /// \brief Create a dependency file for `-d` option.
  ///
  /// This functionality is really only for the benefit of the build system.
  /// It is similar to GCC's `-M*` family of options.
  static int createDependencyFile(const TGParser &Parser, const char *argv0) {
    if (OutputFilename == "-")
      return reportError(argv0, "the option -d must be used together with -o\n");
  
    std::error_code EC;
    ToolOutputFile DepOut(DependFilename, EC, sys::fs::F_Text);
    if (EC)
      return reportError(argv0, "error opening " + DependFilename + ":" +
                                    EC.message() + "\n");
    DepOut.os() << OutputFilename << ":";
    for (const auto &Dep : Parser.getDependencies()) {
      DepOut.os() << ' ' << Dep.first;
    }
    DepOut.os() << "\n";
    DepOut.keep();
    return 0;
  }
  
  int llvm::TableGenMain(char *argv0, TableGenMainFn *MainFn) {
    RecordKeeper Records;
  
    // Parse the input file.
    ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
        MemoryBuffer::getFileOrSTDIN(InputFilename);
    if (std::error_code EC = FileOrErr.getError())
      return reportError(argv0, "Could not open input file '" + InputFilename +
                                    "': " + EC.message() + "\n");
  
    // Tell SrcMgr about this buffer, which is what TGParser will pick up.
    SrcMgr.AddNewSourceBuffer(std::move(*FileOrErr), SMLoc());
  
    // Record the location of the include directory so that the lexer can find
    // it later.
    SrcMgr.setIncludeDirs(IncludeDirs);
  
    TGParser Parser(SrcMgr, Records);
  
    if (Parser.ParseFile())
      return 1;
  
    std::error_code EC;
    ToolOutputFile Out(OutputFilename, EC, sys::fs::F_Text);
    if (EC)
      return reportError(argv0, "error opening " + OutputFilename + ":" +
                                    EC.message() + "\n");
    if (!DependFilename.empty()) {
      if (int Ret = createDependencyFile(Parser, argv0))
        return Ret;
    }
  
    if (MainFn(Out.os(), Records))
      return 1;
  
    if (ErrorsPrinted > 0)
      return reportError(argv0, Twine(ErrorsPrinted) + " errors.\n");
  
    // Declare success.
    Out.keep();
    return 0;
  }
  