Re: PROPOSAL: Extend inline asm syntax with size spec

Segher Boessenkool
2018-10-10T07:55:28Z

On Wed, Oct 10, 2018 at 09:12:48AM +0200, Richard Biener wrote:
> On Tue, 9 Oct 2018, Segher Boessenkool wrote:
> > On Mon, Oct 08, 2018 at 11:07:46AM +0200, Richard Biener wrote:
> > > On Mon, 8 Oct 2018, Segher Boessenkool wrote:
> > > > On Sun, Oct 07, 2018 at 03:53:26PM +0000, Michael Matz wrote:
> > > > > On Sun, 7 Oct 2018, Segher Boessenkool wrote:
> > > > > > On Sun, Oct 07, 2018 at 11:18:06AM +0200, Borislav Petkov wrote:
> > > > > > > Now, Richard suggested doing something like:
> > > > > > >
> > > > > > > 1) inline asm ("...")
> > > > > >
> > > > > > What would the semantics of this be?
> > > > >
> > > > > The size of the inline asm wouldn't be counted towards the inliner size
> > > > > limits (or be counted as "1").
> > > >
> > > > That sounds like a good option.
> > >
> > > Yes, I also like it for simplicity. It also avoids the requirement
> > > of translating the number (in bytes?) given by the user to
> > > "number of GIMPLE instructions" as needed by the inliner.
> >
> > This patch implements this, for C only so far. And the syntax is
> > "asm inline", which is more in line with other syntax.
> >
> > How does this look?
>
> Looks good. A few nits - you need to document this in extend.texi, the

Yup.

> tree flag use needs documenting in tree-core.h,

Ah yes.

> and we need a testcase
> (I'd suggest one that shows we inline a function with "large" asm inline
> () even at -Os).

I have one. Oh, and I probably should do a comment at the one line of
code that isn't just bookkeeping ;-)

> Oh, and I don't think we want C and C++ to diverge - so you need to
> cook up C++ support as well.

Right, that's why I said "C only so far".

> Can kernel folks give this a second and third thought please so we
> don't implement sth that in the end won't satisfy you guys?

Or actually try it out and see if it has the desired effect! Nothing
beats field trials.

I'll do the C++ thing today hopefully, and send things to gcc-patches@.

Segher