From: Uros Bizjak <ubizjak@gmail.com>
To: Alexander Monakov <amonakov@ispras.ru>
Cc: Richard Biener <richard.guenther@gmail.com>,
Jakub Jelinek <jakub@redhat.com>,
GCC Development <gcc@gcc.gnu.org>, X86 ML <x86@kernel.org>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: typeof and operands in named address spaces
Date: Thu, 5 Nov 2020 12:03:10 +0100 [thread overview]
Message-ID: <CAFULd4Z_+o-zb8jbuNKsDJ9ab7xzPsfSo5y8XgYi6=+soht5tQ@mail.gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.20.13.2011051224220.9902@monopod.intra.ispras.ru>
On Thu, Nov 5, 2020 at 10:36 AM Alexander Monakov <amonakov@ispras.ru> wrote:
>
> On Thu, 5 Nov 2020, Uros Bizjak via Gcc wrote:
>
> > > Looks like writing
> > >
> > > typeof((typeof(_var))0) tmp__;
> > >
> > > makes it work. Assumes there's a literal zero for the type of course.
> >
> > This is very limiting assumption, which already breaks for the following test:
>
> To elaborate Richard's idea, you need a way to decay lvalue to rvalue inside
> the typeof to strip the address space; if you need the macro to work for
> more types than just scalar types, the following expression may be useful:
>
> typeof(0?(_var):(_var))
Great, this works well for various operand types.
> (though there's a bug: +(_var) should also suffice for scalar types, but
> somehow GCC keeps the address space on the resulting rvalue)
>
> But I wonder if you actually need this at all:
The posted example is a bit naive, because assignment and basic
operations can be implemented directly, e.g.:
__seg_fs int x;
void
test (void)
{
x &= 1;
}
compiles to:
andl $1, %fs:x(%rip)
without any macro usage at all. However, several operations, such as
xadd and cmpxchg are implemented using assembly templates (see e.g.
arch/x86/include/asm/percpu.h), where local instances are needed.
Uros.
next prev parent reply other threads:[~2020-11-05 11:03 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-04 18:31 Uros Bizjak
2020-11-05 7:26 ` Richard Biener
2020-11-05 8:56 ` Uros Bizjak
2020-11-05 9:36 ` Alexander Monakov
2020-11-05 10:33 ` Uros Bizjak
2020-11-05 11:38 ` Alexander Monakov
2020-11-05 12:00 ` Uros Bizjak
2020-11-05 12:14 ` Alexander Monakov
2020-11-05 12:24 ` Richard Biener
2020-11-05 12:32 ` Uros Bizjak
2020-11-05 12:35 ` Uros Bizjak
2020-11-05 13:22 ` Alexander Monakov
2020-11-05 13:39 ` Alexander Monakov
2020-11-05 13:46 ` Uros Bizjak
2020-11-05 12:26 ` Uros Bizjak
2020-11-05 15:27 ` Andy Lutomirski
2020-11-05 11:03 ` Uros Bizjak [this message]
2020-11-05 9:45 ` Richard Biener
2020-11-05 9:51 ` Jakub Jelinek
2020-11-09 12:47 ` Peter Zijlstra
2020-11-09 19:38 ` Segher Boessenkool
2020-11-09 19:50 ` Nick Desaulniers
2020-11-10 7:57 ` Peter Zijlstra
2020-11-10 18:42 ` Nick Desaulniers
2020-11-10 20:11 ` Peter Zijlstra
2020-11-12 0:40 ` Segher Boessenkool
2020-11-12 0:47 ` Segher Boessenkool
2020-11-10 7:52 ` Peter Zijlstra
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