Re: [boost] [inspect] exceptions (FW: [Boost-users] no exceptions)

Subject: Re: [boost] [inspect] exceptions (FW: [Boost-users] no exceptions)
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-03-28 06:58:05

Brian Wood wrote:
> Robert Kawulak:
> > You can eliminate the try/catch from the code. For example,
> instead of:
> >
> >       try {
> >         // do sth dangerous using cmpRead
> >       } catch(...) {
> >         cmpRead = 0;
> >         throw;
> >       }
> >
> > write:
> >
> >       auto tmp = cmpRead;
> >       cmpRead = 0;
> >       // do sth dangerous using tmp
> >       cmpRead = tmp;
>
>
> Thanks for that.  I tried it.  The implementation is available
> here -- http://webEbenezer.net/misc/rcb.hh .  It's one line shorter
> than the version with the try/catch, but it adds 3 minor statements
> to the non-error path.  On Fedora 14 with g++ 4.5.1 one of my
> executables increased in size by over 500 bytes when using
> the version without a try/catch.   On Windows 7 with MSVC++ 10
> there wasn't any size difference in the executable.  I find the
> try/catch version easier to understand though.

The size growth seems odd on the face of it, given that the variant code is pretty trivial (saving and restoring an int32_t).  Have you looked into the assembly to find the difference?  I can't imagine how an exception handler plus rethrow would take 500 bytes less than the alternative code (three unconditional writes of 32 bits each!).  (Well, I guess one possibility could be that the extra 32b value (tmp) alters register usage and so leads to more instructions to shuffle things to and from main memory.)

Does the size growth buy performance?

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer                     using std::disclaimer;
Dev Tools & Components
Susquehanna International Group, LLP  http://www.sig.com

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