Re: per-file compiler flags?

[Guido Draheim]

Markus Werle wrote:
> Hi!
>
> Consider the following case:
>
> File VeryImportant.C contains code that really needs some
> optimization available. But all other files could (at least during development)
> be compiled without optimization, for the sake of not drinking too much coffee
> due to long compilation times.
>
> Is there a convenient way to achieve the following behaviour:
>
> If (gcc is the compiler)
>    Add to compilation of VeryImportant.C
>    the optimizer flags: CPPFLAGS+="-O9 -finline -funroll-loops"
> else if(intel C++ is the compiler)
>   Add the optimizer flags: CPPFLAGS+="-ip -unroll"
> endif

This is a split question.
(a) per file compile flags:
   - it's an faq and later automake supports it natively by
     recognizing object_CFLAGS specification, in earlier
     versions you would write an explicit rule
     file.o : file.c
        $(COMPILE) .....
(b) special optimization flags
   - this should be adressed in an autoconf check within
     your configure.ac - push it into AC_SUBST(MYFLAGS)
     and add it to rule (a) like
          $(COMPILE) @MYFLAGS@

Supporting special compile switches for gcc vs. non-gcc compilers
has become an interesting topic in the autoconf-archive, there
are now a few of them prepackaged available.

For there were different approaches available to check for the
different styles of compilers, I'm currently testing a method
derived from the variants I've seen. Perhaps you want to take
it as a guideline for your own ac-macro - and perhaps you like
to have it added to the ac-archive as well.

http://ac-archive.sf.net/guidod/ax_cflags_warn_all.html
http://ac-archive.sf.net/guidod/ax_cflags_no_writable_strings.html

-- cheers, guido