Re: No need for object file removal before compilation

[Ralf Wildenhues]

* Ralf Wildenhues wrote on Sat, Apr 12, 2008 at 08:56:24AM CEST:
> OK for the updated one?  It makes for 5% faster
>   libtool --mode=compile gcc -c a.c

I should be more precise: the above holds for an empty file a.c,
measured using a script that calls the above 50 times, pre and post
patch.

I should also note that this patch introduces an inevitable race
(of course all dealing with the "no -c -o" case):

After we grabbed the lockfile, but before we install the trap to remove
it, if the user interrupts libtool in between, we have a leftover
lockfile.  The next compile will barf out, but the error message will
point the user towards the lockfile.

This is benign, and IMNSHO unavoidable.

Cheers,
Ralf

> 2008-04-12  Ralf Wildenhues  <address@hidden>
> 
>       * libltdl/config/ltmain.m4sh (func_mode_compile): Avoid
>       redundant removal of old output files before compilation.
>       Do not remove $obj until we have successfully grabbed the
>       lockfile (in case the compiler doesn't grok `-c -o'), because
>       it might be identical to $output_obj.
>       At the end of the function, before we remove the lockfile,
>       update $removelist so that if the trap hits after the lockfile
>       has been removed, we do not accidentally remove $output_obj that
>       does not belong to us.
>       (func_write_libtool_object): Use $MV instead of mv.