Optimizing repeated calls to AC_TRY_LINK

[Benoit Sigoure]

Hi list,
I have a problem with my boost.m4 macro: it's too slow.  Boost is  
being very unhelpful because it can be installed in many different  
places and the libraries can have many different names.  So what I do  
is that I create all the reasonably possible library names and then  
try to link against each of them for each usual install path (/usr/ 
local/lib, /usr/lib, /opt/local/lib, C:/Boost/lib, etc.).  Even  
though I skip all non existing paths and everything, I end up doing  
several calls to AC_TRY_LINK before I correctly guess the right  
combination of flags to use.  The macro is *much* more reliable than  
other existing macros but embarrassingly slow.  Someone suggested  
something very simple: why not compile conftest.o once and then try  
various combinations of flags to link it?  After all, it's the  
compilation step that takes time (C++, Boost, you know...).   
Unfortunately, I think this is impossible to achieve with current  
Autoconf, because all macros always endup cleaning conftest. 
$ac_objext.  I had to work around this and fiddle with Autoconf  
internals (Forgive me Lord For the wrongs I have done: http:// 
repo.or.cz/w/boost.m4.git?a=commit;h=7e5098a) and I'd like to avoid  
that.

What do you think?
  A. Autoconf can be enhanced to do this sort of thing (what should  
be the interface?  who's in charge of cleaning conftest.$ac_objext?)
  B. Seldom use-case with possibly dangerous effects: learn to live  
with it.
  C. You will burn in Hell for having profaned Autoconf's internals.
  D. The answer D.

Comments welcome.

Cheers,

--
Benoit Sigoure aka Tsuna
EPITA Research and Development Laboratory

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