Hi, has anyone had a chance to look at this?
Kind regards, Daniel On Wed, Jan 18, 2012 at 10:28 PM, Daniel Jasper <[email protected]> wrote: > Hi, > > here is a new version of the proposed change. Changes: > > 1) The warning is more conservative. Members of a class-type can now only > count as unused if a trivial default constructor and a trivial destructor > are used (as these don't have side-effects). A smarter analysis for > side-effect-free constructors and destructors can follow. This prevents > false positives on RAII-style classes. > 2) The warning gives up if a class has a template friend (specializations > of this friend could use any unused member). > 3) Only instantiations of template classes are analyzed, not the template > classes themselves (this was a major source of false positives). > 4) Testcase is include in the patch this time. > > Please let me know, what you think! > > Cheers, > Daniel > > > On Thu, Jan 12, 2012 at 7:26 PM, Daniel Jasper <[email protected]> wrote: > >> Hi Nico, >> >> comments inline. >> >> On Wed, Jan 11, 2012 at 10:49 PM, Nico Weber <[email protected]> wrote: >> >>> Hi Daniel, >>> >>> On Wed, Jan 11, 2012 at 1:11 AM, Daniel Jasper <[email protected]> >>> wrote: >>> > Hi, >>> > >>> > the attached change is designed to detect and warn about private unused >>> > members of C++ classes. It checks whether a class is fully defined in >>> the >>> > current translation unit, i.e. all methods are either defined or pure >>> > virtual and all friends are defined. Otherwise, the private member >>> could be >>> > used by a function defined in another translation unit. >>> >>> that's a cool warning! Here are a few cases where it flags false >>> positives (it finds tons of true positives too, but those are boring >>> :-) ). >>> >>> It flags |stackArray| in ICU's cmemory.h. This is declared for storage >>> and accessed through pointer aliasing, probably not much that can be >>> done about this: >>> >>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/third_party/icu/source/common/cmemory.h&exact_package=chromium&q=file:cmemory.h&l=285 >> >> >> As you said in the other email, it is the wrong code line and I think, it >> is correct to warn about the other |stackArray|. >> >> >>> >>> In flags StaticResource::instance_ in v8's utils.h: >>> >>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/v8/src/utils.h&exact_package=chromium&q=file:v8/src/utils.h&l=300 >>> This is supposed to be accessed through the class below, Access, which >>> is a friend of utils.h. Do you check if any friends use private >>> variables? >>> >> >> Yes, I check friends. This is a bug, I know why it happens (it is because >> of the dependent templates) and I will fix it. >> >> >>> In chromium itself, it flags ShadowingAtExitManager member variables. >>> This is basically a RAII class which only exists to call a protected >>> superclass constructor, and which only exists if UNIT_TESTS is >>> defined: >>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/base/at_exit.h&l=71 >>> So maybe the "constructor without arguments" heuristic could be >>> tweaked to exclude constructors that call superclass constructors with >>> arguments? >>> (Here's another RAII class whose constructor takes 0 arguments: >>> >>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/base/logging_unittest.cc&exact_package=chromium&q=logstatesaver&l=26 >>> ) >>> >> >> I have changed it to be more conservative (I will send a new patch once I >> have fixed the bug mentioned above). It now only accepts members without >> initializer or with an argument-less initializer, if the field's type has a >> trivial default constructor and a trivial destructor. Unfortunately, we now >> also miss a lot of true positives, but I guess the false positives are >> worse, especially because there is no easy way to explicitly suppress the >> warning for these cases within the standard syntax. >> >> Cheers, >> Daniel >> >> >>> >>> (This is not an exhaustive list, just the things I found after a quick >>> look.) >>> >>> Nico >>> >> >> >
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