//== PointerIterationChecker.cpp ------------------------------- -*- C++ -*--=//

//

// 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

//

//===----------------------------------------------------------------------===//

//

// This file defines PointerIterationChecker which checks for non-determinism

// caused due to iteration of unordered containers of pointer elements.

//

//===----------------------------------------------------------------------===//

#include "clang/ASTMatchers/ASTMatchFinder.h"

#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"

#include "clang/StaticAnalyzer/Core/Checker.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"

using namespace clang;

using namespace ento;

using namespace ast_matchers;

namespace {

// ID of a node at which the diagnostic would be emitted.

constexpr llvm::StringLiteral WarnAtNode = "iter";

class PointerIterationChecker : public Checker<check::ASTCodeBody> {

public:

  void checkASTCodeBody(const Decl *D,

                        AnalysisManager &AM,

                        BugReporter &BR) const;

};

static void emitDiagnostics(const BoundNodes &Match, const Decl *D,

                            BugReporter &BR, AnalysisManager &AM,

                            const PointerIterationChecker *Checker) {

  auto *ADC = AM.getAnalysisDeclContext(D);

  const auto *MarkedStmt = Match.getNodeAs<Stmt>(WarnAtNode);

  assert(MarkedStmt);

  auto Range = MarkedStmt->getSourceRange();

  auto Location = PathDiagnosticLocation::createBegin(MarkedStmt,

                                                      BR.getSourceManager(),

                                                      ADC);

  std::string Diagnostics;

  llvm::raw_string_ostream OS(Diagnostics);

  OS << "Iteration of pointer-like elements "

     << "can result in non-deterministic ordering";

  BR.EmitBasicReport(ADC->getDecl(), Checker,

                     "Iteration of pointer-like elements", "Non-determinism",

                     OS.str(), Location, Range);

}

// Assumption: Iteration of ordered containers of pointers is deterministic.

// TODO: Currently, we only check for std::unordered_set. Other unordered

// containers like std::unordered_map also need to be handled.

// TODO: Currently, we do not check what the for loop does with the iterated

// pointer values. Not all iterations may cause non-determinism. For example,

// counting or summing up the elements should not be non-deterministic.

auto matchUnorderedIterWithPointers() -> decltype(decl()) {

  auto UnorderedContainerM = declRefExpr(to(varDecl(hasType(

                               recordDecl(hasName("std::unordered_set")

                             )))));

  auto PointerTypeM = varDecl(hasType(hasCanonicalType(pointerType())));

  auto PointerIterM = stmt(cxxForRangeStmt(

                             hasLoopVariable(PointerTypeM),

                             hasRangeInit(UnorderedContainerM)

                      )).bind(WarnAtNode);

  return decl(forEachDescendant(PointerIterM));

}

void PointerIterationChecker::checkASTCodeBody(const Decl *D,

                                             AnalysisManager &AM,

                                             BugReporter &BR) const {

  auto MatcherM = matchUnorderedIterWithPointers();

  auto Matches = match(MatcherM, *D, AM.getASTContext());

  for (const auto &Match : Matches)

    emitDiagnostics(Match, D, BR, AM, this);

}

} // end of anonymous namespace

void ento::registerPointerIterationChecker(CheckerManager &Mgr) {

  Mgr.registerChecker<PointerIterationChecker>();

}

bool ento::shouldRegisterPointerIterationChecker(const CheckerManager &mgr) {

  const LangOptions &LO = mgr.getLangOpts();

  return LO.CPlusPlus;

}