[PATCH] D12123: [analyzer] Skip Pre/Post handlers for ObjC calls when receiver is nil.

[Devin Coughlin via cfe-commits]

dcoughlin created this revision.
dcoughlin added reviewers: zaks.anna, jordan_rose, xazax.hun.
dcoughlin added a subscriber: cfe-commits.
Herald added a subscriber: aemerson.

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 patch
changes ExprEngineObjC so that VisitObjCMessage skips calling checker
pre/post handlers when the receiver is nil 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 that handles nil receivers
in its PreObjCMessage callback to the new callback.

rdar://problem/18092611

http://reviews.llvm.org/D12123

Files:
  include/clang/StaticAnalyzer/Core/Checker.h
  include/clang/StaticAnalyzer/Core/CheckerManager.h
  lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
  lib/StaticAnalyzer/Core/CheckerManager.cpp
  lib/StaticAnalyzer/Core/ExprEngineObjC.cpp
  test/Analysis/NSContainers.m

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