From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=57362 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1ONwWA-000362-UB
	for qemu-devel@nongnu.org; Sun, 13 Jun 2010 19:23:08 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <rth7680@gmail.com>) id 1ONwT8-0004RY-Sj
	for qemu-devel@nongnu.org; Sun, 13 Jun 2010 19:19:59 -0400
Received: from mail-pw0-f45.google.com ([209.85.160.45]:54622)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <rth7680@gmail.com>) id 1ONwT8-0004RJ-Gg
	for qemu-devel@nongnu.org; Sun, 13 Jun 2010 19:19:58 -0400
Received: by pwj8 with SMTP id 8so2455428pwj.4
	for <qemu-devel@nongnu.org>; Sun, 13 Jun 2010 16:19:57 -0700 (PDT)
Sender: Richard Henderson <rth7680@gmail.com>
Message-ID: <4C156785.8060900@twiddle.net>
Date: Sun, 13 Jun 2010 16:19:33 -0700
From: Richard Henderson <rth@twiddle.net>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH 16/35] tcg-s390: Re-implement tcg_out_movi.
References: <1275678883-7082-1-git-send-email-rth@twiddle.net>
	<1275678883-7082-17-git-send-email-rth@twiddle.net>
	<20100612120443.GM3008@ohm.aurel32.net>
In-Reply-To: <20100612120443.GM3008@ohm.aurel32.net>
Content-Type: text/plain; charset=ISO-8859-15
Content-Transfer-Encoding: 7bit
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, agraf@suse.de

On 06/12/2010 05:04 AM, Aurelien Jarno wrote:
>> +    for (i = 0; i < 4; i++) {
>> +        tcg_target_long mask = 0xffffull << i*16;
>> +        if ((uval & mask) != 0 && (uval & ~mask) == 0) {
> 
> Wouldn't it be simpler to use (uval & mask) == uval ?

Doh.

>> +    /* Try for PC-relative address load.  */
>> +    if ((sval & 1) == 0) {
>> +        intptr_t off = (sval - (intptr_t)s->code_ptr) >> 1;
>> +        if (off == (int32_t)off) {
>> +            tcg_out_insn(s, RIL, LARL, ret, off);
>> +            return;
>> +        }
>> +    }
> 
> Is this part used in practice? There was such a trick on the ARM
> backend, but it was actually never used.

Yes.  The difference here is we have a +- 4GB displacement.

This is primarily used when the extended-immediate facility is not present;
we can generate all even 32-bit constants from LARL, given the placement of
the code_gen_buffer.


r~