[Bug c++/36274] New: Please improve usage of template libs.

[Bug c++/36274] New: Please improve usage of template libs.

[bursig at gmail dot com]

Currently when we want use template libs approach (and not instance template in
all *.o files where it is included) we have to use -fno-implicit-templates
flag. The problem is that this flag change total g++ behavior and "nuke" all
templates which is problematic when we want store only own templates in own
libs.

Please consider "port" Sun CC functionality which allow fetching templates from
external library (*.a/*.so/*.o) during compilation phase via "-instlib" flag.
This flag request on compiler to not emit code for instantiated implicitly
(i.e. by use) templates found in directed libs (-inslib=libXXX.a) and leave
resolving of those code to linker. All libs/objects files added in -instlib=xxx
flag have to be link with target. 

Such functionality will nice improve build time of project which heavily use
templates from external libs (like on Sun CC) and not force us to totally
change project like for -fno-implicit-templates flag.

*.o files (example pch.o):
 - compiler should fetch global and local symbols list.

*.a files:
 - compiler should fetch global and local symbols list.

*.so
 - compiler should fetch global symbols list.


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           Summary: Please improve usage of template libs.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bursig at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

[Bug c++/36274] Please improve usage of template libs.

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2008-05-20 12:42 -------
-frepo is/was supposed to deal with this


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

[Bug c++/36274] Please improve usage of template libs.

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2008-05-20 13:10 -------
Also you might want want to look into the GCC extension (to C++98/C++03) called
extern template whch does the same thing.  Note it is being added to C++0x
already.

-- Pinski


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

[Bug c++/36274] Please improve usage of template libs.

[bursig at gmail dot com]

------- Comment #3 from bursig at gmail dot com  2008-05-20 16:07 -------
(In reply to comment #1)
> -frepo is/was supposed to deal with this
> 
As I know -frepo simple force -fno-implicit-templates which rip all template
instantion from all objects and produce additional special files which are
needed for new/additional pre-link compiler call which inject missing
implementation. I'm not expert here but I suppose that gcc will simple build it
even some of those symbols will be available during link.

Sun propose simpler methodology... compiler know during build phase (via
-instlib) what (and what not) templates instance will be available during link
and simple don't emit code for it. There is no special pre-link phase, no
special files only normal linking (and unknown symbols when you don't and
proper -llibs flags).

As I know Sun CC per-default add stl implementation library via -instlib which
reduce build time of know/"prebuild in lib" stl templates instantions.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

[Bug c++/36274] Please improve usage of template libs.

[bursig at gmail dot com]

------- Comment #4 from bursig at gmail dot com  2008-05-20 16:21 -------
(In reply to comment #2)
> Also you might want want to look into the GCC extension (to C++98/C++03) called
> extern template whch does the same thing.  Note it is being added to C++0x
> already.
> 
> -- Pinski
> 
Yes I know about it and I use it but in large project many libs come form
another teams or another vendors who simple are not interested in such build
time optimizations.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

[Bug c++/36274] Please improve usage of template libs.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think C++ modules will fix this.

[Bug c++/36274] Please improve usage of template libs.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36274

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think it should be closed as WONTFIX, we're not going to implement the
proposal.