Coverage Report

Created: 2020-03-31 06:27

/Users/buildslave/jenkins/workspace/coverage/llvm-project/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp
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//===- GCDAntipatternChecker.cpp ---------------------------------*- C++ -*-==//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines GCDAntipatternChecker which checks against a common
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// antipattern when synchronous API is emulated from asynchronous callbacks
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// using a semaphore:
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//
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//   dispatch_semaphore_t sema = dispatch_semaphore_create(0);
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//
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//   AnyCFunctionCall(^{
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//     // codeā€¦
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//     dispatch_semaphore_signal(sema);
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//   })
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//   dispatch_semaphore_wait(sema, *)
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//
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// Such code is a common performance problem, due to inability of GCD to
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// properly handle QoS when a combination of queues and semaphores is used.
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// Good code would either use asynchronous API (when available), or perform
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// the necessary action in asynchronous callback.
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//
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// Currently, the check is performed using a simple heuristical AST pattern
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// matching.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
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#include "clang/ASTMatchers/ASTMatchFinder.h"
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#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
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#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
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#include "clang/StaticAnalyzer/Core/Checker.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
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#include "llvm/Support/Debug.h"
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using namespace clang;
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using namespace ento;
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using namespace ast_matchers;
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namespace {
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// ID of a node at which the diagnostic would be emitted.
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const char *WarnAtNode = "waitcall";
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class GCDAntipatternChecker : public Checker<check::ASTCodeBody> {
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public:
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  void checkASTCodeBody(const Decl *D,
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                        AnalysisManager &AM,
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                        BugReporter &BR) const;
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};
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decltype(auto) callsName(const char *FunctionName) {
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  return callee(functionDecl(hasName(FunctionName)));
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}
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decltype(auto) equalsBoundArgDecl(int ArgIdx, const char *DeclName) {
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  return hasArgument(ArgIdx, ignoringParenCasts(declRefExpr(
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                                 to(varDecl(equalsBoundNode(DeclName))))));
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}
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decltype(auto) bindAssignmentToDecl(const char *DeclName) {
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  return hasLHS(ignoringParenImpCasts(
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                         declRefExpr(to(varDecl().bind(DeclName)))));
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}
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/// The pattern is very common in tests, and it is OK to use it there.
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/// We have to heuristics for detecting tests: method name starts with "test"
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/// (used in XCTest), and a class name contains "mock" or "test" (used in
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/// helpers which are not tests themselves, but used exclusively in tests).
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static bool isTest(const Decl *D) {
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  if (const auto* ND = dyn_cast<NamedDecl>(D)) {
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    std::string DeclName = ND->getNameAsString();
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    if (StringRef(DeclName).startswith("test"))
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      return true;
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  }
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  if (const auto *OD = dyn_cast<ObjCMethodDecl>(D)) {
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    if (const auto *CD = dyn_cast<ObjCContainerDecl>(OD->getParent())) {
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      std::string ContainerName = CD->getNameAsString();
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      StringRef CN(ContainerName);
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      if (CN.contains_lower("test") || 
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)
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        return true;
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    }
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  }
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  return false;
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}
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static auto findGCDAntiPatternWithSemaphore() -> decltype(compoundStmt()) {
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  const char *SemaphoreBinding = "semaphore_name";
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  auto SemaphoreCreateM = callExpr(allOf(
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      callsName("dispatch_semaphore_create"),
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      hasArgument(0, ignoringParenCasts(integerLiteral(equals(0))))));
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  auto SemaphoreBindingM = anyOf(
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      forEachDescendant(
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          varDecl(hasDescendant(SemaphoreCreateM)).bind(SemaphoreBinding)),
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      forEachDescendant(binaryOperator(bindAssignmentToDecl(SemaphoreBinding),
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                     hasRHS(SemaphoreCreateM))));
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  auto HasBlockArgumentM = hasAnyArgument(hasType(
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            hasCanonicalType(blockPointerType())
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            ));
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  auto ArgCallsSignalM = hasAnyArgument(stmt(hasDescendant(callExpr(
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          allOf(
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              callsName("dispatch_semaphore_signal"),
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              equalsBoundArgDecl(0, SemaphoreBinding)
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              )))));
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  auto HasBlockAndCallsSignalM = allOf(HasBlockArgumentM, ArgCallsSignalM);
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  auto HasBlockCallingSignalM =
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    forEachDescendant(
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      stmt(anyOf(
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        callExpr(HasBlockAndCallsSignalM),
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        objcMessageExpr(HasBlockAndCallsSignalM)
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           )));
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  auto SemaphoreWaitM = forEachDescendant(
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    callExpr(
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      allOf(
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        callsName("dispatch_semaphore_wait"),
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        equalsBoundArgDecl(0, SemaphoreBinding)
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      )
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    ).bind(WarnAtNode));
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  return compoundStmt(
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      SemaphoreBindingM, HasBlockCallingSignalM, SemaphoreWaitM);
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}
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static auto findGCDAntiPatternWithGroup() -> decltype(compoundStmt()) {
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  const char *GroupBinding = "group_name";
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  auto DispatchGroupCreateM = callExpr(callsName("dispatch_group_create"));
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  auto GroupBindingM = anyOf(
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      forEachDescendant(
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          varDecl(hasDescendant(DispatchGroupCreateM)).bind(GroupBinding)),
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      forEachDescendant(binaryOperator(bindAssignmentToDecl(GroupBinding),
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                     hasRHS(DispatchGroupCreateM))));
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  auto GroupEnterM = forEachDescendant(
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      stmt(callExpr(allOf(callsName("dispatch_group_enter"),
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                          equalsBoundArgDecl(0, GroupBinding)))));
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  auto HasBlockArgumentM = hasAnyArgument(hasType(
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            hasCanonicalType(blockPointerType())
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            ));
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  auto ArgCallsSignalM = hasAnyArgument(stmt(hasDescendant(callExpr(
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          allOf(
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              callsName("dispatch_group_leave"),
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              equalsBoundArgDecl(0, GroupBinding)
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              )))));
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  auto HasBlockAndCallsLeaveM = allOf(HasBlockArgumentM, ArgCallsSignalM);
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  auto AcceptsBlockM =
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    forEachDescendant(
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      stmt(anyOf(
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        callExpr(HasBlockAndCallsLeaveM),
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        objcMessageExpr(HasBlockAndCallsLeaveM)
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           )));
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  auto GroupWaitM = forEachDescendant(
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    callExpr(
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      allOf(
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        callsName("dispatch_group_wait"),
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        equalsBoundArgDecl(0, GroupBinding)
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      )
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    ).bind(WarnAtNode));
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  return compoundStmt(GroupBindingM, GroupEnterM, AcceptsBlockM, GroupWaitM);
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}
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static void emitDiagnostics(const BoundNodes &Nodes,
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                            const char* Type,
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                            BugReporter &BR,
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                            AnalysisDeclContext *ADC,
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                            const GCDAntipatternChecker *Checker) {
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  const auto *SW = Nodes.getNodeAs<CallExpr>(WarnAtNode);
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  assert(SW);
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  std::string Diagnostics;
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  llvm::raw_string_ostream OS(Diagnostics);
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  OS << "Waiting on a callback using a " << Type << " creates useless threads "
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     << "and is subject to priority inversion; consider "
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     << "using a synchronous API or changing the caller to be asynchronous";
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  BR.EmitBasicReport(
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    ADC->getDecl(),
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    Checker,
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    /*Name=*/"GCD performance anti-pattern",
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    /*BugCategory=*/"Performance",
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    OS.str(),
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    PathDiagnosticLocation::createBegin(SW, BR.getSourceManager(), ADC),
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    SW->getSourceRange());
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}
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void GCDAntipatternChecker::checkASTCodeBody(const Decl *D,
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                                             AnalysisManager &AM,
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                                             BugReporter &BR) const {
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  if (isTest(D))
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    return;
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  AnalysisDeclContext *ADC = AM.getAnalysisDeclContext(D);
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  auto SemaphoreMatcherM = findGCDAntiPatternWithSemaphore();
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  auto Matches = match(SemaphoreMatcherM, *D->getBody(), AM.getASTContext());
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  for (BoundNodes Match : Matches)
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    emitDiagnostics(Match, "semaphore", BR, ADC, this);
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  auto GroupMatcherM = findGCDAntiPatternWithGroup();
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  Matches = match(GroupMatcherM, *D->getBody(), AM.getASTContext());
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  for (BoundNodes Match : Matches)
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    emitDiagnostics(Match, "group", BR, ADC, this);
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}
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} // end of anonymous namespace
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void ento::registerGCDAntipattern(CheckerManager &Mgr) {
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  Mgr.registerChecker<GCDAntipatternChecker>();
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}
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bool ento::shouldRegisterGCDAntipattern(const CheckerManager &mgr) {
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  return true;
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}