[analyzer] Skip Pre/Post handlers for ObjC calls when receiver is nil.

In Objective-C, method calls with nil receivers are essentially no-ops. They
do not fault (although the returned value may be garbage depending on the
declared return type and architecture). Programmers are aware of this
behavior and will complain about a false alarm when the analyzer
diagnoses API violations for method calls when the receiver is known to
be nil.

Rather than require each individual checker to be aware of this behavior
and suppress a warning when the receiver is nil, this commit
changes ExprEngineObjC so that VisitObjCMessage skips calling checker
pre/post handlers when the receiver is definitely nil. Instead, it adds a
new event, ObjCMessageNil, that is only called in that case.

The CallAndMessageChecker explicitly cares about this case, so I've changed it
to add a callback for ObjCMessageNil and moved the logic in PreObjCMessage
that handles nil receivers to the new callback.

rdar://problem/18092611

Differential Revision: http://reviews.llvm.org/D12123

llvm-svn: 247653

1 files changed, 39 insertions, 8 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/CheckerManager.cpp b/clang/lib/StaticAnalyzer/Core/CheckerManager.cpp
index d26a76abe8e..c464d301b6e 100644
--- a/clang/lib/StaticAnalyzer/Core/CheckerManager.cpp
+++ b/clang/lib/StaticAnalyzer/Core/CheckerManager.cpp
@@ -177,7 +177,9 @@ void CheckerManager::runCheckersForStmt(bool isPreVisit,
 namespace {
   struct CheckObjCMessageContext {
     typedef std::vector<CheckerManager::CheckObjCMessageFunc> CheckersTy;
-    bool IsPreVisit, WasInlined;
+
+    ObjCMessageVisitKind Kind;
+    bool WasInlined;
     const CheckersTy &Checkers;
     const ObjCMethodCall &Msg;
     ExprEngine &Eng;
@@ -185,14 +187,28 @@ namespace {
     CheckersTy::const_iterator checkers_begin() { return Checkers.begin(); }
     CheckersTy::const_iterator checkers_end() { return Checkers.end(); }
 
-    CheckObjCMessageContext(bool isPreVisit, const CheckersTy &checkers,
+    CheckObjCMessageContext(ObjCMessageVisitKind visitKind,
+                            const CheckersTy &checkers,
                             const ObjCMethodCall &msg, ExprEngine &eng,
                             bool wasInlined)
-      : IsPreVisit(isPreVisit), WasInlined(wasInlined), Checkers(checkers),
+      : Kind(visitKind), WasInlined(wasInlined), Checkers(checkers),
         Msg(msg), Eng(eng) { }
 
     void runChecker(CheckerManager::CheckObjCMessageFunc checkFn,
                     NodeBuilder &Bldr, ExplodedNode *Pred) {
+
+      bool IsPreVisit;
+
+      switch (Kind) {
+        case ObjCMessageVisitKind::Pre:
+          IsPreVisit = true;
+          break;
+        case ObjCMessageVisitKind::MessageNil:
+        case ObjCMessageVisitKind::Post:
+          IsPreVisit = false;
+          break;
+      }
+
       const ProgramPoint &L = Msg.getProgramPoint(IsPreVisit,checkFn.Checker);
       CheckerContext C(Bldr, Eng, Pred, L, WasInlined);
 
@@ -202,19 +218,29 @@ namespace {
 }
 
 /// \brief Run checkers for visiting obj-c messages.
-void CheckerManager::runCheckersForObjCMessage(bool isPreVisit,
+void CheckerManager::runCheckersForObjCMessage(ObjCMessageVisitKind visitKind,
                                                ExplodedNodeSet &Dst,
                                                const ExplodedNodeSet &Src,
                                                const ObjCMethodCall &msg,
                                                ExprEngine &Eng,
                                                bool WasInlined) {
-  CheckObjCMessageContext C(isPreVisit,
-                            isPreVisit ? PreObjCMessageCheckers
-                                       : PostObjCMessageCheckers,
-                            msg, Eng, WasInlined);
+  auto &checkers = getObjCMessageCheckers(visitKind);
+  CheckObjCMessageContext C(visitKind, checkers, msg, Eng, WasInlined);
   expandGraphWithCheckers(C, Dst, Src);
 }
 
+const std::vector<CheckerManager::CheckObjCMessageFunc> &
+CheckerManager::getObjCMessageCheckers(ObjCMessageVisitKind Kind) {
+  switch (Kind) {
+  case ObjCMessageVisitKind::Pre:
+    return PreObjCMessageCheckers;
+    break;
+  case ObjCMessageVisitKind::Post:
+    return PostObjCMessageCheckers;
+  case ObjCMessageVisitKind::MessageNil:
+    return ObjCMessageNilCheckers;
+  }
+}
 namespace {
   // FIXME: This has all the same signatures as CheckObjCMessageContext.
   // Is there a way we can merge the two?
@@ -616,6 +642,11 @@ void CheckerManager::_registerForPostStmt(CheckStmtFunc checkfn,
 void CheckerManager::_registerForPreObjCMessage(CheckObjCMessageFunc checkfn) {
   PreObjCMessageCheckers.push_back(checkfn);
 }
+
+void CheckerManager::_registerForObjCMessageNil(CheckObjCMessageFunc checkfn) {
+  ObjCMessageNilCheckers.push_back(checkfn);
+}
+
 void CheckerManager::_registerForPostObjCMessage(CheckObjCMessageFunc checkfn) {
   PostObjCMessageCheckers.push_back(checkfn);
 }