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Date:   Wed, 10 Oct 2018 12:29:03 +0200 (CEST)
From:   Richard Biener <rguenther@suse.de>
To:     Segher Boessenkool <segher@kernel.crashing.org>
cc:     Ingo Molnar <mingo@kernel.org>, Michael Matz <matz@suse.de>,
        Borislav Petkov <bp@alien8.de>, gcc@gcc.gnu.org,
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        Sam Ravnborg <sam@ravnborg.org>,
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: PROPOSAL: Extend inline asm syntax with size spec
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On Wed, 10 Oct 2018, Segher Boessenkool wrote:

> On Wed, Oct 10, 2018 at 09:22:40AM +0200, Ingo Molnar wrote:
> > * Richard Biener <rguenther@suse.de> wrote:
> > > 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?
> > 
> > So this basically passes '0 size' to the inliner, which should be better
> > than passing in the explicit size, as we'd inevitably get it wrong
> > in cases.
> 
> The code immediately after this makes it size 1, even for things like
> asm(""), I suppose this works better for the inliner.  But that's a detail
> (and it might change); the description says "consider this asm as minimum
> length and cost for inlining decisions", which works for either 0 or 1.

It was made 1 as otherwise the inliner happily explodes on

void foo () { asm(""); foo(); }

> > I also like 'size 0' for the reason that we tend to write assembly code
> > and mark it 'inline' if we really think it matters to performance,
> > so making it more likely to be inlined when used within another inline
> > function is a plus as well.
> 
> You can think of it as meaning "we want this asm inlined always", and then
> whether that actually happens depends on if the function around it is
> inlined or not.

Richard.