Hi!
> > > (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> > > MEANING. It's a pure optimization that doesn't actually change
> > > anything else. If you don't do the optimization, absolutely nothing
> > > changes.
> >
> > And if the parser is well written the optimisation
On Sat, Mar 6, 2021 at 5:07 AM Miguel Ojeda
wrote:
>
> Concerning #pragma once: I actually would like to have a standard
> #once directive if what is a "seen file" could be defined a bit more
> precisely.
I think it would be ok if you had something like
#pragma once IDTOKEN
which would basic
On Fri, Mar 5, 2021 at 10:25 PM Linus Torvalds
wrote:
>
> And regardless of even _those_ issues, you still should do all the
> other syntactic tokenization stuff (ie all the quoting, the the
> character handling: 'a' is a valid C token, but if you see the string
> "it's" outside of a comment, that
On Fri, Mar 5, 2021 at 1:19 AM David Laight wrote:
>
> The point is that you can skip the unwanted parts of
> #if without having to parse the file at all.
> You just need to detect the line breaks.
That's not actually true AT ALL.
You still need to at the very least parse the preprocessor tokens
From: Linus Torvalds
> Sent: 04 March 2021 20:16
>
> On Thu, Mar 4, 2021 at 5:55 AM David Laight wrote:
> >
> > > (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> > > MEANING. It's a pure optimization that doesn't actually change
> > > anything else. If you don't do the op
On Thu, Mar 4, 2021 at 5:55 AM David Laight wrote:
>
> > (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> > MEANING. It's a pure optimization that doesn't actually change
> > anything else. If you don't do the optimization, absolutely nothing
> > changes.
>
> And if the par
> (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> MEANING. It's a pure optimization that doesn't actually change
> anything else. If you don't do the optimization, absolutely nothing
> changes.
And if the parser is well written the optimisation is probably
irrelevant compa
On Wed, Mar 3, 2021 at 11:46 AM Tom Tromey wrote:
>
> It's also worth noting that in GCC it is slower than include guards.
> See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58770
>
> It's just a bug, probably easy to fix. On the other hand, nobody has
> ever bothered to do so.
That bugzilla is
On Sun, Feb 28, 2021 at 10:34:46PM +0300, Alexey Dobriyan wrote:
>
> gcc does
>
> open "/" + "whatever between quotes"
> fstat
>
> so that "1.h" and "./1.h" differ
When I try the following with GCC 10.2:
$ cat header.h
#pragma once
#include "./header.h"
On Sun, Feb 28, 2021 at 11:34 AM Alexey Dobriyan wrote:
>
> >
> > End result: #pragma is fundamentally less reliable than the
> > traditional #ifdef guard. The #ifdef guard works fine even if you
> > re-read the file for whatever reason, while #pragma relies on some
> > kind of magical behavior.
On Sun, Feb 28, 2021 at 09:46:17AM -0800, Linus Torvalds wrote:
> On Sun, Feb 28, 2021 at 8:57 AM Alexey Dobriyan wrote:
> >
> > This is bulk deletion of preprocessor include guards and conversion
> > to #pragma once directive.
>
> So as mentioned earlier, I'm not 100% convinced about the advanta
On Sun, Feb 28, 2021 at 8:57 AM Alexey Dobriyan wrote:
>
> This is bulk deletion of preprocessor include guards and conversion
> to #pragma once directive.
So as mentioned earlier, I'm not 100% convinced about the advantage of
#pragma once.
But I decided to actually test it, and it turns out tha
This is bulk deletion of preprocessor include guards and conversion
to #pragma once directive.
See [PATCH 11/11] and [PATCH 12/11] for the script and rationale.
Everything else is trivial stuff.
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