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

Fri Sep 25 11:09:40 PDT 2015

I see. Thank you very much, David. 

Date: Fri, 25 Sep 2015 10:51:35 -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 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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