On Tue, Nov 12, 2013 at 9:56 PM, Richard Smith <[email protected]>wrote:
> On Tue, Nov 12, 2013 at 9:44 PM, Richard Trieu <[email protected]> wrote: > >> Timing details: >> >> 21.03s for Clang >> 21.27s for Patched Clang with warning >> >> This is a difference of .24s or less than 1.5% slowdown. >> >> Times are averaged over 20 runs. Input is the same pre-processed file. >> Both Clang binaries were built from the same revision. -fsyntax-only was >> also used. >> > > What's your test case? > Portion of Clang driver code. > Is this some randomly-chosen file or is it selected to be the worst case > for this warning somehow? > Randomly chosen. > A 1.5% slowdown on average seems like far too much for this. Was this in a > setup where the CFG was being built regardless (for instance, with > -Wuninitialized enabled)? > I used the standard Clang invocation. I am not sure if that constructs the CFG. Turning -Wuninitialized on and off produces similar timing differences to this warning. > > >> On Fri, Nov 8, 2013 at 10:47 PM, Sean Silva <[email protected]> wrote: >> >>> >>> >>> >>> On Fri, Nov 8, 2013 at 8:52 PM, Chandler Carruth >>> <[email protected]>wrote: >>> >>>> Random thoughts... >>>> >>>> On Fri, Nov 8, 2013 at 3:20 PM, Sean Silva <[email protected]> wrote: >>>> >>>>> At a higher level, is this really needed as a compiler warning? I >>>>> mean, it's nice and all to detect these things statically, but is this >>>>> really something that needs to be happening on every build? >>>> >>>> >>>> Note that if this is a significant compile time issue, that's relevant. >>>> Everything else is assuming that it isn't. =] >>>> >>>> Could we just do this in the static analyzer? In practice, I can't >>>>> imagine any of these being hard to debug "while developing", since they >>>>> will always result in a stack overflow the second they are called (and >>>>> then >>>>> you just look at the core file (or the debugger that your IDE attached) to >>>>> see which function it was) >>>> >>>> >>>> Your description alone is the evidence for why developers should have a >>>> warning. ;] First off, stack overflows are notoriously annoying to debug. >>>> Core files are often missing. Running under the debugger is yet another >>>> step to do. I would much rather the compiler just tell me about it. >>>> >>> >>> Absolutely; a static warning is always preferable. All my comments were >>> in light of a perception that this was maybe not cheap enough to justify >>> running at every compile (of course, need to wait for Richard to respond >>> with some real measurements of the compile time impact). >>> >>> -- Sean Silva >>> >>> >>>> >>>> Almost all of our warnings "aren't needed" because they could be tested >>>> and debugged. That doesn't remove their value. >>>> >>>> >>>>> So essentially it seems like this is finding bugs in code that has no >>>>> test coverage and has never been executed in practice; that kind of >>>>> "cleaning out crusty unused parts of the codebase" seems like it would be >>>>> better left to the static analyzer. >>>> >>>> >>>> No, it's shortening the cycle time for developers that hit this bug. >>>> >>>> It also is cleaning out bugs in crufty code, which is always nice. Very >>>> few people will run the static analyzer over all of their crufty code >>>> because if they aren't changing it and it is working in production, they >>>> aren't going to want to sift through the false positives of "maybe that's a >>>> bug". Static analyzers run much more over code under active development. >>>> >>>> And fundamentally, we *routinely* do all of the static analysis that is >>>> sufficiently inexpensive and has sufficiently rare false positives at >>>> compile time. So I think we should focus on those two criteria, the latter >>>> one being the most interesting here. >>>> >>>> _______________________________________________ >>>> cfe-commits mailing list >>>> [email protected] >>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >>>> >>>> >>> >>> _______________________________________________ >>> cfe-commits mailing list >>> [email protected] >>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >>> >>> >> >> _______________________________________________ >> cfe-commits mailing list >> [email protected] >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >> >> >
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