[Analyzer] Assume that string-like const globals are non-nil.

Differential Revision: https://reviews.llvm.org/D38764

llvm-svn: 315488

2 files changed, 135 insertions, 0 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt b/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt
index 32520e74073..bf9d3610d5e 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt
+++ b/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt
@@ -57,6 +57,7 @@ add_clang_library(clangStaticAnalyzerCheckers
   NSErrorChecker.cpp
   NoReturnFunctionChecker.cpp
   NonNullParamChecker.cpp
+  NonnullStringConstantsChecker.cpp
   NullabilityChecker.cpp
   NumberObjectConversionChecker.cpp
   ObjCAtSyncChecker.cpp
diff --git a/clang/lib/StaticAnalyzer/Checkers/NonnullStringConstantsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/NonnullStringConstantsChecker.cpp
new file mode 100644
index 00000000000..47b33045416
--- /dev/null
+++ b/clang/lib/StaticAnalyzer/Checkers/NonnullStringConstantsChecker.cpp
@@ -0,0 +1,134 @@
+//==- NonnullStringConstantsChecker.cpp ---------------------------*- C++ -*--//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This checker adds an assumption that constant string-like globals are
+//  non-null, as otherwise they generally do not convey any useful information.
+//  The assumption is useful, as many framework use such global const strings,
+//  and the analyzer might not be able to infer the global value if the
+//  definition is in a separate translation unit.
+//  The following types (and their typedef aliases) are considered string-like:
+//   - `char* const`
+//   - `const CFStringRef` from CoreFoundation
+//   - `NSString* const` from Foundation
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+
+class NonnullStringConstantsChecker : public Checker<check::Location> {
+  mutable IdentifierInfo *NSStringII = nullptr;
+  mutable IdentifierInfo *CFStringRefII = nullptr;
+
+public:
+  NonnullStringConstantsChecker() {}
+
+  void checkLocation(SVal l, bool isLoad, const Stmt *S,
+                     CheckerContext &C) const;
+
+private:
+  void initIdentifierInfo(ASTContext &Ctx) const;
+
+  bool isGlobalConstString(SVal V) const;
+
+  bool isStringlike(QualType Ty) const;
+};
+
+} // namespace
+
+/// Lazily initialize cache for required identifier informations.
+void NonnullStringConstantsChecker::initIdentifierInfo(ASTContext &Ctx) const {
+  if (NSStringII)
+    return;
+
+  NSStringII = &Ctx.Idents.get("NSString");
+  CFStringRefII = &Ctx.Idents.get("CFStringRef");
+}
+
+/// Add an assumption that const string-like globals are non-null.
+void NonnullStringConstantsChecker::checkLocation(SVal location, bool isLoad,
+                                                 const Stmt *S,
+                                                 CheckerContext &C) const {
+  initIdentifierInfo(C.getASTContext());
+  if (!isLoad || !location.isValid())
+    return;
+
+  ProgramStateRef State = C.getState();
+  SVal V = State->getSVal(location.castAs<Loc>());
+
+  if (isGlobalConstString(location)) {
+    Optional<DefinedOrUnknownSVal> Constr = V.getAs<DefinedOrUnknownSVal>();
+
+    if (Constr) {
+
+      // Assume that the variable is non-null.
+      ProgramStateRef OutputState = State->assume(*Constr, true);
+      C.addTransition(OutputState);
+    }
+  }
+}
+
+/// \param V loaded lvalue.
+/// \return whether {@code val} is a string-like const global.
+bool NonnullStringConstantsChecker::isGlobalConstString(SVal V) const {
+  Optional<loc::MemRegionVal> RegionVal = V.getAs<loc::MemRegionVal>();
+  if (!RegionVal)
+    return false;
+  auto *Region = dyn_cast<VarRegion>(RegionVal->getAsRegion());
+  if (!Region)
+    return false;
+  const VarDecl *Decl = Region->getDecl();
+
+  if (!Decl->hasGlobalStorage())
+    return false;
+
+  QualType Ty = Decl->getType();
+  bool HasConst = Ty.isConstQualified();
+  if (isStringlike(Ty) && HasConst)
+    return true;
+
+  // Look through the typedefs.
+  while (auto *T = dyn_cast<TypedefType>(Ty)) {
+    Ty = T->getDecl()->getUnderlyingType();
+
+    // It is sufficient for any intermediate typedef
+    // to be classified const.
+    HasConst = HasConst || Ty.isConstQualified();
+    if (isStringlike(Ty) && HasConst)
+      return true;
+  }
+  return false;
+}
+
+/// \return whether {@code type} is a string-like type.
+bool NonnullStringConstantsChecker::isStringlike(QualType Ty) const {
+
+  if (Ty->isPointerType() && Ty->getPointeeType()->isCharType())
+    return true;
+
+  if (auto *T = dyn_cast<ObjCObjectPointerType>(Ty)) {
+    return T->getInterfaceDecl()->getIdentifier() == NSStringII;
+  } else if (auto *T = dyn_cast<TypedefType>(Ty)) {
+    return T->getDecl()->getIdentifier() == CFStringRefII;
+  }
+  return false;
+}
+
+void ento::registerNonnullStringConstantsChecker(CheckerManager &Mgr) {
+  Mgr.registerChecker<NonnullStringConstantsChecker>();
+}