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

Adrian Bunk
2005-12-29T19:14:21Z

On Thu, Dec 29, 2005 at 10:42:41AM -0500, Jakub Jelinek wrote:
> On Thu, Dec 29, 2005 at 04:35:29PM +0100, Adrian Bunk wrote:
> > > You describe a nice utopia where only the most essential functions are
> > > inlined.. but so far that hasn't worked out all that well ;) Turning
> > > "inline" back into the hint to the compiler that the C language makes it
> > > is maybe a cop-out, but it's a sustainable approach at least.
> > >...
> >
> > But shouldn't nowadays gcc be able to know best even without an "inline"
> > hint?
>
> Only for static functions (and in -funit-at-a-time mode).

I'm assuming -funit-at-a-time mode. Currently it's disabled on i386, but
this will change in the medium-term future.

> Anything else would require full IMA over the whole kernel and we aren't
> there yet. So inline hints are useful. But most of the inline keywords
> in the kernel really should be that, hints, because e.g. while it can be

Are there (on !alpha) any places in the kernel where a function is
inline but not static, and this is wanted?

> beneficial to inline something on one arch, it may be not beneficial on
> another arch, depending on cache sizes, number of general registers
> available to the compiler, register preassure, speed of the call/ret
> pair, calling convention and many other factors.

Does gcc really need hints when the functions are static?

> Jakub

cu
Adrian

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