llvm dev - Jan 2011 - [LLVMdev] include/Config/config.h discrepancies between CMake and autofoo builds

Hello. I see many discrepancies in config.h file generated by CMake and
autoheader.

Most of them are following:
In autofoo-generated config:
> /* Define to 1 if you have the `<name>' function. */
> #define HAVE_<name> 1
>
but in CMake-generated:
> #undef HAVE_<name>
>
This happens because in config.h.cmake (config.h.in analog) these functions
just are not checked for.

Another difference:
autofoo sets this by default:
> #define ENABLE_PIC 1
>
while CMake not.

There are many other differencies, which bother me, so here is the question:
is it harmless and if not - should i try to fix it?
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arrowdodger <6yearold at gmail.com> writes:
> Hello. I see many discrepancies in config.h file generated by CMake and
> autoheader.
>
> Most of them are following:
> In autofoo-generated config:
>
>> /* Define to 1 if you have the `<name>' function. */
>> #define HAVE_<name> 1
>>
> but in CMake-generated:
>
>> #undef HAVE_<name>
>>
> This happens because in config.h.cmake (config.h.in analog) these functions
> just are not checked for.
Right.
> Another difference:
> autofoo sets this by default:
>
>> #define ENABLE_PIC 1
>>
> while CMake not.
>
> There are many other differencies, which bother me, so here is the
question:
> is it harmless and if not - should i try to fix it?
AFAIK a typical autoconf setup does not start from scratch. It reuses
scripts or templates taken from some other project or from autoconf
itself. This means that lots of stuff listed on config.h is not
actually used by the LLVM C++ sources. The macro ENABLE_PIC is one
example.

config.h.cmake was derived from config.h.in and not all tests were
implemented. It would be nice to test them all, just for the sake of
coherence. Or to say it with other words: patches welcome.

On Jan 4, 2011, at 7:45 AM, arrowdodger wrote:
> Hello. I see many discrepancies in config.h file generated by CMake and
autoheader.
> 
> Most of them are following:
> In autofoo-generated config:
> /* Define to 1 if you have the `<name>' function. */
> #define HAVE_<name> 1
> but in CMake-generated:
> #undef HAVE_<name>
> This happens because in config.h.cmake (config.h.in analog) these functions
just are not checked for.
> 
We may just not use those functions anymore - do you have a list of these?
> Another difference:
> autofoo sets this by default:
> #define ENABLE_PIC 1
> while CMake not.
> 
This is more concerning - maybe it's a windows specific problem that came
along?

-eric

>
> We may just not use those functions anymore - do you have a list of these?
>
Yes, i've started to make up a list of those functions, but it haven't
finished yet.

> This is more concerning - maybe it's a windows specific problem that
came
> along?
>
Not sure, i haven't look yet for CMake checking code itself. By the way,
i'm
using FreeBSD.

Or to say it with other words: patches welcome.
>
So, how should i proceed? Make CMake-generated config to be identical to
autotools one? Or cleanup both headers from unused stuff by Eric's
suggestion?
The latter seems more complex to me, since i see no other way except
grep'ing all code for #define's and remove those, which aren't used
anywhere.
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