1 files changed, 166 insertions, 0 deletions
diff --git a/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp
new file mode 100644
index 00000000000..51a3fc19386
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+++ b/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp
@@ -0,0 +1,166 @@
+//===- GCDAntipatternChecker.cpp ---------------------------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines GCDAntipatternChecker which checks against a common
+// antipattern when synchronous API is emulated from asynchronous callbacks
+// using a semaphore:
+//
+//   dispatch_semaphore_t sema = dispatch_semaphore_create(0);
+//
+//   AnyCFunctionCall(^{
+//     // code…
+//     dispatch_semaphore_signal(sema);
+//   })
+//   dispatch_semaphore_wait(sema, *)
+//
+// Such code is a common performance problem, due to inability of GCD to
+// properly handle QoS when a combination of queues and semaphores is used.
+// Good code would either use asynchronous API (when available), or perform
+// the necessary action in asynchronous callback.
+//
+// Currently, the check is performed using a simple heuristical AST pattern
+// matching.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
+#include "llvm/Support/Debug.h"
+
+using namespace clang;
+using namespace ento;
+using namespace ast_matchers;
+
+namespace {
+
+const char *WarningBinding = "semaphore_wait";
+
+class GCDAntipatternChecker : public Checker<check::ASTCodeBody> {
+public:
+  void checkASTCodeBody(const Decl *D,
+                        AnalysisManager &AM,
+                        BugReporter &BR) const;
+};
+
+class Callback : public MatchFinder::MatchCallback {
+  BugReporter &BR;
+  const GCDAntipatternChecker *C;
+  AnalysisDeclContext *ADC;
+
+public:
+  Callback(BugReporter &BR,
+           AnalysisDeclContext *ADC,
+           const GCDAntipatternChecker *C) : BR(BR), C(C), ADC(ADC) {}
+
+  virtual void run(const MatchFinder::MatchResult &Result) override;
+};
+
+auto callsName(const char *FunctionName)
+    -> decltype(callee(functionDecl())) {
+  return callee(functionDecl(hasName(FunctionName)));
+}
+
+auto equalsBoundArgDecl(int ArgIdx, const char *DeclName)
+    -> decltype(hasArgument(0, expr())) {
+  return hasArgument(ArgIdx, ignoringParenCasts(declRefExpr(
+                                 to(varDecl(equalsBoundNode(DeclName))))));
+}
+
+auto bindAssignmentToDecl(const char *DeclName) -> decltype(hasLHS(expr())) {
+  return hasLHS(ignoringParenImpCasts(
+                         declRefExpr(to(varDecl().bind(DeclName)))));
+}
+
+void GCDAntipatternChecker::checkASTCodeBody(const Decl *D,
+                                               AnalysisManager &AM,
+                                               BugReporter &BR) const {
+
+  // The pattern is very common in tests, and it is OK to use it there.
+  if (const auto* ND = dyn_cast<NamedDecl>(D)) {
+    std::string DeclName = ND->getNameAsString();
+    if (StringRef(DeclName).startswith("test"))
+      return;
+  }
+  if (const auto *OD = dyn_cast<ObjCMethodDecl>(D)) {
+    if (const auto *CD = dyn_cast<ObjCContainerDecl>(OD->getParent())) {
+      std::string ContainerName = CD->getNameAsString();
+      StringRef CN(ContainerName);
+      if (CN.contains_lower("test") || CN.contains_lower("mock"))
+        return;
+    }
+  }
+
+  const char *SemaphoreBinding = "semaphore_name";
+  auto SemaphoreCreateM = callExpr(callsName("dispatch_semaphore_create"));
+
+  auto SemaphoreBindingM = anyOf(
+      forEachDescendant(
+          varDecl(hasDescendant(SemaphoreCreateM)).bind(SemaphoreBinding)),
+      forEachDescendant(binaryOperator(bindAssignmentToDecl(SemaphoreBinding),
+                     hasRHS(SemaphoreCreateM))));
+
+  auto SemaphoreWaitM = forEachDescendant(
+    callExpr(
+      allOf(
+        callsName("dispatch_semaphore_wait"),
+        equalsBoundArgDecl(0, SemaphoreBinding)
+      )
+    ).bind(WarningBinding));
+
+  auto HasBlockArgumentM = hasAnyArgument(hasType(
+            hasCanonicalType(blockPointerType())
+            ));
+
+  auto ArgCallsSignalM = hasArgument(0, hasDescendant(callExpr(
+          allOf(
+              callsName("dispatch_semaphore_signal"),
+              equalsBoundArgDecl(0, SemaphoreBinding)
+              ))));
+
+  auto HasBlockAndCallsSignalM = allOf(HasBlockArgumentM, ArgCallsSignalM);
+
+  auto AcceptsBlockM =
+    forEachDescendant(
+      stmt(anyOf(
+        callExpr(HasBlockAndCallsSignalM),
+        objcMessageExpr(HasBlockAndCallsSignalM)
+           )));
+
+  auto FinalM = compoundStmt(SemaphoreBindingM, SemaphoreWaitM, AcceptsBlockM);
+
+  MatchFinder F;
+  Callback CB(BR, AM.getAnalysisDeclContext(D), this);
+
+  F.addMatcher(FinalM, &CB);
+  F.match(*D->getBody(), AM.getASTContext());
+}
+
+void Callback::run(const MatchFinder::MatchResult &Result) {
+  const auto *SW = Result.Nodes.getNodeAs<CallExpr>(WarningBinding);
+  assert(SW);
+  BR.EmitBasicReport(
+      ADC->getDecl(), C,
+      /*Name=*/"Semaphore performance anti-pattern",
+      /*Category=*/"Performance",
+      "Waiting on a semaphore with Grand Central Dispatch creates useless "
+      "threads and is subject to priority inversion; consider "
+      "using a synchronous API or changing the caller to be asynchronous",
+      PathDiagnosticLocation::createBegin(SW, BR.getSourceManager(), ADC),
+      SW->getSourceRange());
+}
+
+}
+
+void ento::registerGCDAntipattern(CheckerManager &Mgr) {
+  Mgr.registerChecker<GCDAntipatternChecker>();
+}