[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, 10 insertions, 0 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp b/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp
index 86955c4fcb0..37b84480f89 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp
@@ -38,6 +38,7 @@ class CheckerDocumentation : public Checker< check::PreStmt<ReturnStmt>,
                                        check::PostStmt<DeclStmt>,
                                        check::PreObjCMessage,
                                        check::PostObjCMessage,
+                                       check::ObjCMessageNil,
                                        check::PreCall,
                                        check::PostCall,
                                        check::BranchCondition,
@@ -95,6 +96,15 @@ public:
   /// check::PostObjCMessage
   void checkPostObjCMessage(const ObjCMethodCall &M, CheckerContext &C) const {}
 
+  /// \brief Visit an Objective-C message whose receiver is nil.
+  ///
+  /// This will be called when the analyzer core processes a method call whose
+  /// receiver is definitely nil. In this case, check{Pre/Post}ObjCMessage and
+  /// check{Pre/Post}Call will not be called.
+  ///
+  /// check::ObjCMessageNil
+  void checkObjCMessageNil(const ObjCMethodCall &M, CheckerContext &C) const {}
+
   /// \brief Pre-visit an abstract "call" event.
   ///
   /// This is used for checkers that want to check arguments or attributed