revng-revng/lib/Decompiler/CDecompilerPass.cpp

//
// Copyright rev.ng Srls. See LICENSE.md for details.
//

#include <system_error>

#include "llvm/ADT/SmallString.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/IRReader/IRReader.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"

#include "clang/Tooling/CommonOptionsParser.h"
#include "clang/Tooling/Tooling.h"

#include "revng/Support/IRHelpers.h"

#include "revng-c/Decompiler/CDecompilerPass.h"
#include "revng-c/Decompiler/DLALayouts.h"
#include "revng-c/DecompilerResourceFinder/ResourceFinder.h"
#include "revng-c/PHIASAPAssignmentInfo/PHIASAPAssignmentInfo.h"
#include "revng-c/RestructureCFGPass/ASTTree.h"
#include "revng-c/RestructureCFGPass/RestructureCFG.h"
#include "revng-c/TargetFunctionOption/TargetFunctionOption.h"

#include "CDecompilerAction.h"

using namespace llvm;
using namespace clang;
using namespace clang::tooling;

using PHIIncomingMap = SmallMap<llvm::PHINode *, unsigned, 4>;
using BBPHIMap = SmallMap<llvm::BasicBlock *, PHIIncomingMap, 4>;
using DuplicationMap = std::map<const llvm::BasicBlock *, size_t>;

static cl::OptionCategory RevNgCategory("revng options");

using llvm::cl::NumOccurrencesFlag;

// Prefix for the decompiled output filename.
static cl::opt<std::string> DecompiledDir("decompiled-dir",
                                          cl::desc("decompiled code dir"),
                                          cl::value_desc("decompiled-dir"),
                                          cl::cat(RevNgCategory),
                                          NumOccurrencesFlag::Optional);

// Prefix for the short circuit metrics dir.
static cl::opt<std::string> OutputPath("short-circuit-metrics-output-dir",
                                       cl::desc("Short circuit metrics dir"),
                                       cl::value_desc("short-circuit-dir"),
                                       cl::cat(RevNgCategory),
                                       NumOccurrencesFlag::Optional);

char CDecompilerPass::ID = 0;

using Register = RegisterPass<CDecompilerPass>;
static Register X("decompilation", "Decompilation Pass", false, false);

CDecompilerPass::CDecompilerPass(std::unique_ptr<llvm::raw_ostream> Out) :
  llvm::FunctionPass(ID), Out(std::move(Out)) {
}

CDecompilerPass::CDecompilerPass() : CDecompilerPass(nullptr) {
}

bool CDecompilerPass::runOnFunction(llvm::Function &F) {

  ShortCircuitCounter = 0;
  TrivialShortCircuitCounter = 0;

  if (not F.getMetadata("revng.func.entry"))
    return false;

  // If the `-single-decompilation` option was passed from command line, skip
  // decompilation for all the functions that are not the selected one.
  if (not TargetFunction.empty())
    if (not F.getName().equals(TargetFunction.c_str()))
      return false;

  // If the -decompiled-dir flag was passed, the decompiled function needs to be
  // written to file, in the specified directory.
  // We initialize Out with a proper file descriptor to make it happen.
  if (not DecompiledDir.empty()) {

    // We only support the -decompiled-dir flag when the pass is
    // default-constructed. If it's not, Out already contains a raw_ostream that
    // should be used to emit the decompiled C code, so using the
    // -decompiled-dir flag would overwrite it, with surprising results.
    // For now we don't need it. If we ever happen to need it, we will figure
    // out what's the best thing to do depending on the real scenario.
    revng_assert(not Out);

    if (auto Error = llvm::sys::fs::create_directories(DecompiledDir))
      revng_abort(Error.message().c_str());

    std::string FileName = DecompiledDir + '/' + F.getName().data() + ".c";
    std::error_code Error;
    auto WriteOnlyFlag = llvm::sys::fs::FileAccess::FA_Write;
    Out = std::make_unique<llvm::raw_fd_ostream>(FileName,
                                                 Error,
                                                 WriteOnlyFlag);
    if (Error) {
      Out.reset();
      revng_abort(Error.message().c_str());
    }
  }

  // If the --short-circuit-metrics-output-dir=dir argument was passed from
  // command line, we need to print the statistics for the short circuit metrics
  // into a file with the function name, inside the directory 'dir'.

  std::unique_ptr<llvm::raw_fd_ostream> StatsFileStream;
  if (auto NumOutPaths = OutputPath.getNumOccurrences()) {
    revng_assert(NumOutPaths < 2);

    if (auto Error = llvm::sys::fs::create_directories(OutputPath))
      revng_abort(Error.message().c_str());

    std::string FileName = OutputPath + '/' + F.getName().data();
    std::error_code Error;
    auto WriteOnlyFlag = llvm::sys::fs::FileAccess::FA_Write;
    StatsFileStream = std::make_unique<llvm::raw_fd_ostream>(FileName,
                                                             Error,
                                                             WriteOnlyFlag);

    if (Error) {
      StatsFileStream.reset();
      revng_abort(Error.message().c_str());
    }
  }

  // This is a hack to prevent clashes between LLVM's `opt` arguments and
  // clangTooling's CommonOptionParser arguments.
  // At this point opt's arguments have already been parsed, so there should
  // be no problem in clearing the map and let clangTooling reinitialize it
  // with its own stuff.
  cl::getRegisteredOptions().clear();

  // Construct the path of the include (hack copied from revng-lift). Even if
  // the include path is unique for now, we have anyway set up the search in
  // multiple paths.
  static std::string RevNgCIncludeFile;
  auto &FileFinder = revng::c::ResourceFinder;
  auto OptionalRevNgIncludeFile = FileFinder.findFile("share/revngc/"
                                                      "revng-c-include.c");
  revng_assert(OptionalRevNgIncludeFile.has_value());
  RevNgCIncludeFile = OptionalRevNgIncludeFile.value();

  // Here we build the artificial command line for clang tooling
  static std::array<const char *, 5> ArgV = {
    "revng-c",  RevNgCIncludeFile.data(),
    "--", // separator between tool arguments and clang arguments
    "-xc", // tell clang to compile C language
    "-std=c11", // tell clang to compile C11
  };
  static int ArgC = ArgV.size();
  static CommonOptionsParser OptionParser(ArgC, ArgV.data(), RevNgCategory);
  ClangTool RevNg = ClangTool(OptionParser.getCompilations(),
                              OptionParser.getSourcePathList());

  // Get the Abstract Syntax Tree of the restructured code.
  auto &RestructureCFGAnalysis = getAnalysis<RestructureCFG>();
  ASTTree &GHAST = RestructureCFGAnalysis.getAST();

  // Get information about which instructions are marked to be serialized.
  const auto &Mark = getAnalysis<MarkForSerializationPass>().getMap();

  // Get information about serialization of PHI nodes.
  auto &PHIASAPAssignments = getAnalysis<PHIASAPAssignmentInfo>();
  BBPHIMap PHIMap = PHIASAPAssignments.extractBBToPHIIncomingMap();

  // Get the results of the Data Layout Analysis, if present.
  // If DLA has been executed, we also need to get the ScalarEvolution, because
  // we will use it in decompilation to transform pointer arithmetics into
  // access to structs' fields.
  // Eventually, when we will integrate revng's Model, the DLA results will not
  // be necessary anymore. We'll only need to check if the Model contains type
  // information.
  auto *DLA = getAnalysisIfAvailable<DLAPass>();
  const dla::ValueLayoutMap *LayoutMap = nullptr;
  llvm::ScalarEvolution *SE = nullptr;
  if (DLA) {
    LayoutMap = DLA->getLayoutMap();
    SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
  }

  CDecompilerAction
    Decompilation(F, GHAST, PHIMap, LayoutMap, SE, Mark, std::move(Out));

  using FactoryUniquePtr = std::unique_ptr<FrontendActionFactory>;
  FactoryUniquePtr Factory = newFrontendActionFactory(&Decompilation);
  RevNg.run(Factory.get());

  // Serialize the collected metrics in the statistics file if necessary
  if (StatsFileStream) {
    *StatsFileStream << "function,short-circuit,trivial-short-circuit\n"
                     << F.getName().data() << "," << ShortCircuitCounter << ","
                     << TrivialShortCircuitCounter << "\n";
  }

  return true;
}