Hi and thanks to the contributors of g++ (and the whole gcc suite) ...
what a tremendous value!
If I have to pinpoint my question, I would refer to gcc internals
documentation section 11.10.4 "Functions for C++", macro name
DECL_LINKONCE_P which is said to be "Not yet implemented".
Then the question is "Can we expect further (compile-and-link time)
efficiencies when this internal DECL_LINKONCE_P is implemented in a
later release in the 4.X series?
I assume the answer is no, as long as COMDAT support is provided in the
linker. If such is the case, the suggestion is to add e.g. "The
usefulness of DECL_LINKONCE_P appears questionable because COMDAT
support by the link process is needed anyway for avoiding object code
duplication and DECL_LINKONCE_P has no influence on this matter."
Generally, the optimization of template instantiations remains a bit
obscure for the g++ user. The performance improvement announced with gcc
4.5 seems unrelated to the COMDAT optimization of executable size. Is
this correct?
On one project, I used -fno-implicit-templates since I felt that a
static library build process would benefit from it (every anticipated
template specializations is included in the library). On another
project, I felt a need to use -frepo (I don't recall exactly why). While
trying to merge the two projects, I found that the g++ compiler (with
GNU ld) was working just fine with the default setting for template
specializations. Seems great!
(Thinking while I write now, maybe DECL_LINKONCE_P might be relevant to
distinguish compilation runs with -frepo in contexts where the link
process does not support COMDAT.)
If you follow my thinking (I'm not sure I always do when applying
advanced C++ abstraction in actual code development), I wish to have an
understanding of compile-time efficiencies when the C++ template
mechanism is heavily used. More specifically, I am afraid that
compile-time would become un-manageable as a project grows from a code
base just too heavily dependent on the STL. But the STL concepts are so
attractive!
Once upon a time there was the Borland model ... I guess g++ makes this
a thing of the past. Is this a fair assessment?
Best regards.
--
- Thierry Moreau
CONNOTECH Experts-conseils inc.
