Re: don't let libtool infer the tag (was: sysroot support in libtool)

[Mike Frysinger]

On Sunday 13 April 2008, Ralf Wildenhues wrote:
> * Ralf Wildenhues wrote on Sun, Apr 13, 2008 at 10:26:11PM CEST:
> > * Richard Purdie wrote on Sun, Apr 13, 2008 at 08:53:10PM CEST:
> > > tag.patch - The tag errors were breaking things for no good reason so
> > > we turned the error into a warning
> >
> > Well, don't come crying for bad performance to us if you do things like
> > this.  Letting libtool infer the tag is rather expensive, at least
> > relatively, for 2.2.2 on modern systems where there are few other forks
> > needed.
>
> I guess I should substantiate this claim.  Taking a libtool script of
> current CVS HEAD, plus one approved but not applied patch, configuring
> it for CC=gcc, where gcc is a symlink to gcc-4.3.  Then, adding your
> patch (so that libtool doesn't error out on the following); then running
>   ./libtool --mode=compile gcc-4.3 -c a.c
>
> 100 times on an empty file a.c takes:
> 4.24user 1.60system 0:05.91elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+2400outputs (0major+745403minor)pagefaults 0swaps
>
> whereas doing the same with a tag given:
>   ./libtool --tag=CC --mode=compile gcc-4.3 -c a.c
>
> takes:
> 1.99user 0.82system 0:02.87elapsed 97%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+2400outputs (0major+316064minor)pagefaults 0swaps
>
> Of course, this is an extreme case, as the source file is empty, and the
> libtool script generated by the Libtool package supports several tags
> (it will try them all).
>
> So don't do this, please.  Supply --tag=CC if your compiler name doesn't
> match.

i doubt people will care at this point, but ive done a bit of work in Gentoo 
to make the tag inferring "better".  ive done this as there are still a few 
packages out there that insist on using libtool found in $PATH.  we've been 
killing them off over time, but we still havent gotten them all, so this 
painful patch lives on.
http://sources.gentoo.org/sys-devel/libtool/files/1.5.6/libtool-1.5-filter-host-tags.patch
-mike

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