Re: [patch 00/2] improve .text size on gcc 4.0 and newer compilers

Linus Torvalds
2005-12-28T21:02:38Z

On Wed, 28 Dec 2005, Arjan van de Ven wrote:
>
> yup that's why the patch only does it for gcc4, in which the inlining
> heuristics finally got rewritten to something that seems to resemble
> sanity...

Is that actually true of all gcc4 versions? I seem to remember gcc-4.0
being a real stinker.

> > Also, the inlining patch apparently makes code larger in some cases,
> > so it's not even a unconditional win.
>
> .... as long as you give the inlining algorithm enough information.
> -fno-unit-at-a-time prevents gcc from having the information, and the
> decisions it makes are then less optimal...
>
> (unit-at-a-time allows gcc to look at the entire .c file, eg things like
> number of callers etc etc, disabling that tells gcc to do the .c file as
> single pass top-to-bottom only)

I'd still prefer to see numbers with -funit-at-a-time only. I think it's
an independent knob, and I'd be much less worried about that, because we
do know that unit-at-a-time has been enabled on x86-64 for a long time
("forever"). So that's less of a change, I feel.

Linus