[clang][analyzer] Split NullDereferenceChecker into a modeling and checker part.

The checker currently reports beneath the null dereference dereferences
of undefined value and of label addresses. If we want to add more kinds
of invalid dereferences (or split the existing functionality) it is more
useful to make it separate checkers.
To make this possible the existing checker is split into a
DereferenceModeling part and a NullDereference checker that actually
only switches on the check of null dereference. This is similar
architecture as in MallocChecker and CStringChecker.

The change is almost NFC but a new (modeling) checker is added.
If the NullDereference checker is turned off the found invalid
dereferences will still stop the analysis without emitted warning
(this is different compared to the old behavior).

Author: balazske

clang/include/clang/StaticAnalyzer/Checkers/Checkers.td

@@ -206,7 +206,12 @@ def CallAndMessageChecker : Checker<"CallAndMessage">,
   Documentation<HasDocumentation>,
   Dependencies<[CallAndMessageModeling]>;
 
-def DereferenceChecker : Checker<"NullDereference">,
+def DereferenceModeling : Checker<"DereferenceModeling">,
+  HelpText<"General support for dereference related checkers">,
+  Documentation<HasDocumentation>,
+  Hidden;
+
+def NullDereferenceChecker : Checker<"NullDereference">,
   HelpText<"Check for dereferences of null pointers">,
   CheckerOptions<[
     CmdLineOption<Boolean,
@@ -215,7 +220,8 @@ def DereferenceChecker : Checker<"NullDereference">,
                   "true",
                   Released>
   ]>,
-  Documentation<HasDocumentation>;
+  Documentation<HasDocumentation>,
+  Dependencies<[DereferenceModeling]>;
 
 def NonNullParamChecker : Checker<"NonNullParamChecker">,
   HelpText<"Check for null pointers passed as arguments to a function whose "

clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp

@@ -33,12 +33,6 @@ class DereferenceChecker
                       EventDispatcher<ImplicitNullDerefEvent> > {
   enum DerefKind { NullPointer, UndefinedPointerValue, AddressOfLabel };
 
-  BugType BT_Null{this, "Dereference of null pointer", categories::LogicError};
-  BugType BT_Undef{this, "Dereference of undefined pointer value",
-                   categories::LogicError};
-  BugType BT_Label{this, "Dereference of the address of a label",
-                   categories::LogicError};
-
   void reportBug(DerefKind K, ProgramStateRef State, const Stmt *S,
                  CheckerContext &C) const;
 
@@ -56,6 +50,12 @@ class DereferenceChecker
                              bool loadedFrom = false);
 
   bool SuppressAddressSpaces = false;
+
+  bool CheckNullDereference = false;
+
+  std::unique_ptr<BugType> BT_Null;
+  std::unique_ptr<BugType> BT_Undef;
+  std::unique_ptr<BugType> BT_Label;
 };
 } // end anonymous namespace
 
@@ -155,22 +155,27 @@ static bool isDeclRefExprToReference(const Expr *E) {
 
 void DereferenceChecker::reportBug(DerefKind K, ProgramStateRef State,
                                    const Stmt *S, CheckerContext &C) const {
+  if (!CheckNullDereference) {
+    C.addSink();
+    return;
+  }
+
   const BugType *BT = nullptr;
   llvm::StringRef DerefStr1;
   llvm::StringRef DerefStr2;
   switch (K) {
   case DerefKind::NullPointer:
-    BT = &BT_Null;
+    BT = BT_Null.get();
     DerefStr1 = " results in a null pointer dereference";
     DerefStr2 = " results in a dereference of a null pointer";
     break;
   case DerefKind::UndefinedPointerValue:
-    BT = &BT_Undef;
+    BT = BT_Undef.get();
     DerefStr1 = " results in an undefined pointer dereference";
     DerefStr2 = " results in a dereference of an undefined pointer value";
     break;
   case DerefKind::AddressOfLabel:
-    BT = &BT_Label;
+    BT = BT_Label.get();
     DerefStr1 = " results in an undefined pointer dereference";
     DerefStr2 = " results in a dereference of an address of a label";
     break;
@@ -351,12 +356,24 @@ void DereferenceChecker::checkBind(SVal L, SVal V, const Stmt *S,
   C.addTransition(State, this);
 }
 
-void ento::registerDereferenceChecker(CheckerManager &mgr) {
-  auto *Chk = mgr.registerChecker<DereferenceChecker>();
-  Chk->SuppressAddressSpaces = mgr.getAnalyzerOptions().getCheckerBooleanOption(
-      mgr.getCurrentCheckerName(), "SuppressAddressSpaces");
+void ento::registerDereferenceModeling(CheckerManager &Mgr) {
+  Mgr.registerChecker<DereferenceChecker>();
+}
+
+bool ento::shouldRegisterDereferenceModeling(const CheckerManager &Mgr) {
+  return true;
+}
+
+void ento::registerNullDereferenceChecker(CheckerManager &Mgr) {
+  auto *Chk = Mgr.getChecker<DereferenceChecker>();
+  Chk->CheckNullDereference = true;
+  Chk->SuppressAddressSpaces = Mgr.getAnalyzerOptions().getCheckerBooleanOption(
+      Mgr.getCurrentCheckerName(), "SuppressAddressSpaces");
+  Chk->BT_Null.reset(new BugType(Mgr.getCurrentCheckerName(), "Dereference of null pointer", categories::LogicError));
+  Chk->BT_Undef.reset(new BugType(Mgr.getCurrentCheckerName(), "Dereference of undefined pointer value", categories::LogicError));
+  Chk->BT_Label.reset(new BugType(Mgr.getCurrentCheckerName(), "Dereference of the address of a label", categories::LogicError));
 }
 
-bool ento::shouldRegisterDereferenceChecker(const CheckerManager &mgr) {
+bool ento::shouldRegisterNullDereferenceChecker(const CheckerManager &Mgr) {
   return true;
 }

clang/test/Analysis/analyzer-enabled-checkers.c

@@ -14,6 +14,7 @@
 // CHECK-NEXT: core.BitwiseShift
 // CHECK-NEXT: core.CallAndMessageModeling
 // CHECK-NEXT: core.CallAndMessage
+// CHECK-NEXT: core.DereferenceModeling
 // CHECK-NEXT: core.DivideZero
 // CHECK-NEXT: core.DynamicTypePropagation
 // CHECK-NEXT: core.NonNullParamChecker

clang/test/Analysis/std-c-library-functions-arg-enabled-checkers.c

@@ -22,6 +22,7 @@
 // CHECK-NEXT: core.BitwiseShift
 // CHECK-NEXT: core.CallAndMessageModeling
 // CHECK-NEXT: core.CallAndMessage
+// CHECK-NEXT: core.DereferenceModeling
 // CHECK-NEXT: core.DivideZero
 // CHECK-NEXT: core.DynamicTypePropagation
 // CHECK-NEXT: core.NonNullParamChecker