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From: Adonis Ling <adonis0147@gmail.com>
To: Alexander Monakov <amonakov@ispras.ru>
Cc: gcc-help@gcc.gnu.org
Subject: Re: Why does different types of array subscript used to iterate affect auto vectorization
Date: Tue, 28 Jun 2022 23:47:16 +0800	[thread overview]
Message-ID: <CAG5qfXjCHGV1RraJDXCHmwqJhZQ82iL3Qmwpf-Aj8xbF=M2mDw@mail.gmail.com> (raw)
In-Reply-To: <3b44a272-447c-28d7-678d-5968df7ec248@ispras.ru>

On Tue, Jun 28, 2022 at 11:38 PM Alexander Monakov <amonakov@ispras.ru>
wrote:

> On Tue, 28 Jun 2022, Adonis Ling via Gcc-help wrote:
>
> > > Here the main problem is '*array' and 'nread' have the same type, so
> they
> > > might overlap. Ideally the compiler would recognize that that cannot
> happen
> > > because it would make 'array[nread++] = i' undefined due to unsequenced
> > > modifications, but GCC is not sufficiently smart (yet). The secondary
> issue
> > > is the same as below:
> > >
> >
> > I got your point.
> >
> > After that, I tried to add __restrict__ to nread as the following shows
> and
> > GCC still doesn't optimize it.
>
> As I said, there's a secondary issue even if you add 'restrict'.
>
> Alexander
>

For the secondary issue, could I explain that Clang chooses to ignore it?

-- 
Best regards,
Adonis

  reply	other threads:[~2022-06-28 15:47 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-27  2:47 Adonis Ling
2022-06-28 13:06 ` Alexander Monakov
2022-06-28 15:23   ` Adonis Ling
2022-06-28 15:38     ` Alexander Monakov
2022-06-28 15:47       ` Adonis Ling [this message]
2022-06-28 15:56         ` Alexander Monakov
2022-06-28 16:00           ` Adonis Ling

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