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Date: Tue, 17 Nov 2009 19:18:00 -0000
From: Eli Zaretskii <eliz@gnu.org>
Subject: Re: [patch 3/4] Fix hw watchpoints #2: reordered / simultaneously hit
In-reply-to: <20091117152912.GA29979@host0.dyn.jankratochvil.net>
To: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: brobecker@adacore.com, gdb-patches@sourceware.org
Reply-to: Eli Zaretskii <eliz@gnu.org>
Message-id: <83fx8dm05c.fsf@gnu.org>
References: <20091116034156.GD22701@host0.dyn.jankratochvil.net> <20091117001056.GE4557@adacore.com> <83k4xpn6hz.fsf@gnu.org> <20091117141139.GA5266@adacore.com> <20091117152912.GA29979@host0.dyn.jankratochvil.net>
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> Date: Tue, 17 Nov 2009 16:29:12 +0100
> From: Jan Kratochvil <jan.kratochvil@redhat.com>
> Cc: Eli Zaretskii <eliz@gnu.org>, gdb-patches@sourceware.org
> 
>  0000000000000000 <get>:
>     0:  0f b6 47 04             movzbl 0x4(%rdi),%eax
> +   4:  83 e0 01                and    $0x1,%eax
>         c3                      retq   
>  
>  0000000000000010 <set>:
> -  10:  c6 47 04 01             movb   $0x1,0x4(%rdi)
> +  10:  80 4f 04 01             orb    $0x1,0x4(%rdi)

This is what I remembered, at least for x86.  A single additional
instruction can hardly cause any visible slowdown, at least not with
access patterns typical for such flags.

Any other reasons not to use bitfields?