[cfe-users] optimize template-heavy project with duplicate code removal

[David Blaikie via cfe-users]

On Thu, Sep 24, 2015 at 4:46 PM, chen xu <chenxuz at outlook.com> wrote:

> That's very helpful. Thanks a lot. I will try them out.
>
> By the way, when linking two libraries, say, they both instantiate classes
> from the same template class (e.g. defined in a 'common' component), into
> an executable, will the linker remove the duplicate class instance?
>

The linker will remove the duplicate code, but not the duplicate debug info
(unless you use -fdebug-types-section - which will actually make your
object files a little bigger, but the executable will be smaller since the
duplicates will be removed)


>
>
> ------------------------------
> Date: Thu, 24 Sep 2015 15:29:09 -0700
>
> Subject: Re: [cfe-users] optimize template-heavy project with duplicate
> code removal
> From: dblaikie at gmail.com
> To: chenxuz at outlook.com
> CC: cfe-users at lists.llvm.org
>
>
>
> On Thu, Sep 24, 2015 at 3:12 PM, chen xu <chenxuz at outlook.com> wrote:
>
> Thanks, David.  The build type is Debug. Today I tried removing the debug
> info (-g), the size of the executable could be cut 90%, to around 100MB,
> which looks not bad. Do you know whether there is a way to separate debug
> info file from the executable file on Linux?
>
>
> Yep, -gsplit-dwarf - latest versions of GDB can cope with this debug info
>
> You can also compress the debug info: -Wa,--compress-debug-sections
>
> If you want linked debug info (rather than split debug info), consider
> enabling type units to deduplicate debug info in your final executable
> (-fdebug-types-section).
>
>
>  Mainly our code is already there, refactoring might require big effort..
> Also, does clang support -fno-implicit-templates? if yes, maybe we could
> use it to eliminate duplicate template instances to control the final size.
>
>
> Not sure, off hand, whether Clang supports that.
>
>
>
> ------------------------------
> Date: Wed, 23 Sep 2015 16:59:04 -0700
> Subject: Re: [cfe-users] optimize template-heavy project with duplicate
> code removal
> From: dblaikie at gmail.com
> To: chenxuz at outlook.com
> CC: cfe-users at lists.llvm.org
>
>
> debug or non-debug build?
>
> & no, for a full release build, measuring the final executable size,
> there's not much you can do with the compiler.
>
> you can try to factor common portions out of your templates (eg: remove
> template parameters where possible - if, for example, a member function of
> a class template doesn't need all the template parameters - pull it out
> into a standalone function template that takes fewer template parameters,
> and call it from the member one)
>
> On Wed, Sep 23, 2015 at 4:43 PM, chen xu via cfe-users <
> cfe-users at lists.llvm.org> wrote:
>
> Hi, our project heavily uses c++ template, and the resulting executable is
> almost 1.5G Bytes, which is too big to be acceptable. Adding -O2 or -Os
> does not seem helping. Is there any way (like link option, etc) to reduce
> the size?
>
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>
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