my-front-end.cpp

#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Host.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/DiagnosticOptions.h"
#include "clang/Basic/FileManager.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/TargetOptions.h"
#include "clang/Frontend/ASTConsumers.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Parse/Parser.h"
#include "clang/Parse/ParseAST.h"
#include <iostream>

using namespace llvm;
using namespace clang;


// option for the program
// input file
static cl::opt<std::string> FileName(cl::Positional, cl::desc("Input file"), cl::Required);

int
main(int argc, char **argv)
{
    // necessary always to parse command line
    cl::ParseCommandLineOptions(argc, argv, "My front end example\n");

    /*
    *   this class will manage entire infrastructure to handle compilation
    *   clang -cc1 commonly instantiate a specific FrontendAction, which
    *   will perform all steps here covered, but we will do all the steps
    *   by our own.
    */
    CompilerInstance CI;
    DiagnosticOptions diagnosticOptions; // code diagnostics
    CI.createDiagnostics();

    std::shared_ptr<TargetOptions>  PTO(new TargetOptions());
    PTO->Triple = sys::getDefaultTargetTriple();
    TargetInfo *PTI = TargetInfo::CreateTargetInfo(CI.getDiagnostics(), PTO);
    CI.setTarget(PTI);

    // initialization code of file manager necessary to read source files
    CI.createFileManager();
    // the source manager will be responsible for managing SourceLocation used in lexer and parser
    CI.createSourceManager(CI.getFileManager());
    // preprocessor
    CI.createPreprocessor(TU_Complete);
    CI.getPreprocessorOpts().UsePredefines = false;

    // AST Consumer to consume final AST (after parsing and semantic analysis)
    // if we wanted to generate LLVM IR, we would have to provide specific code
    // generation ASTConsumer instance (called BackendConsumer).
    // this time we just create an AST consumer that prints AST to console
    ASTConsumer *astConsumer = CreateASTPrinter(NULL,"");
    // set AST Consumer
    CI.setASTConsumer(astConsumer);
    // AST Context (used by parser) and semantics (used by semantic analysis)
    CI.createASTContext();
    CI.createSema(TU_Complete, NULL);

    const FileEntry *pFile = CI.getFileManager().getFile(FileName);
    if (!pFile)
    {
        std::cerr << "File not found: " << FileName << std::endl;
        return 1;
    }

    CI.getSourceManager().setMainFileID(
        CI.getSourceManager().createFileID(
            pFile, SourceLocation(), SrcMgr::C_User
        )
    );

    CI.getDiagnosticClient().BeginSourceFile(CI.getLangOpts(), 0);
    // peform lexical and syntactic analysis
    ParseAST(CI.getSema());
    CI.getASTContext().PrintStats();
    CI.getDiagnosticClient().EndSourceFile();
    return 0;
}