From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:43459)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <Claudio.Fontana@huawei.com>) id 1UhEAL-0005kF-OO
	for qemu-devel@nongnu.org; Tue, 28 May 2013 03:18:08 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <Claudio.Fontana@huawei.com>) id 1UhEA8-0004rk-2y
	for qemu-devel@nongnu.org; Tue, 28 May 2013 03:17:53 -0400
Received: from lhrrgout.huawei.com ([194.213.3.17]:4028)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <Claudio.Fontana@huawei.com>) id 1UhEA7-0004qp-Cm
	for qemu-devel@nongnu.org; Tue, 28 May 2013 03:17:39 -0400
Message-ID: <51A459F8.5030706@huawei.com>
Date: Tue, 28 May 2013 09:17:12 +0200
From: Claudio Fontana <claudio.fontana@huawei.com>
MIME-Version: 1.0
References: <5141F36E.10004@huawei.com> <519DCEC8.8060000@huawei.com>
	<519DD0BF.4090702@huawei.com> <519E43EE.6090702@twiddle.net>
	<519F2A8F.6090903@huawei.com> <519F9D11.9020603@twiddle.net>
	<51A346EC.2080005@huawei.com> <51A3AA3A.4050406@twiddle.net>
In-Reply-To: <51A3AA3A.4050406@twiddle.net>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 2/4] tcg/aarch64: implement new TCG target
	for aarch64
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/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: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Richard Henderson <rth@twiddle.net>
Cc: Peter Maydell <peter.maydell@linaro.org>, Jani Kokkonen <Jani.Kokkonen@huawei.com>, qemu-devel@nongnu.org

On 27.05.2013 20:47, Richard Henderson wrote:
> On 2013-05-27 04:43, Claudio Fontana wrote:
>>> Hmm, true.  Although I'd been thinking more along the lines of
>>> arranging the code such that we'd use movz to set the zero.
>>
>> I think we need to keep treating zero specially if we want to keep the optimization where we don't emit needless MOVK instructions for half-words of value 0000h.
>>
>> I can however make one single function out of movi32 and movi64, it could look like this:
>>
>> if (!value) {
>>      tcg_out_movr(s, 0, rd, TCG_REG_ZXR);
>>      return;
>> }
>>
>> base = (value > 0xffffffff) ? 0xd2800000 : 0x52800000;
>>
>> while (value) {
>>      /* etc etc */
>> }
> 
> 
>     if (type == TCG_TYPE_I32) {
>         value = (uint32_t)value;
>         ext = 0;
>     } else if (value <= 0xffffffff) {
>         ext = 0;
>     } else {
>         ext = 0x80000000;
>     }

The check for type is probably unnecessary, since we don't gain anything (we still have to check something once), so I'd rather use a uint64_t parameter and then just check for value < 0xffffffff.

> 
>     base = 0x52800000;  /* MOVZ */
>     do {
>         int shift = ctz64(value) & (63 & -16);
>         int half = (value >> shift) & 0xffff;
>         tcg_out32(s, base | ext | half << 5 | rd);
>         value &= ~(0xffffUL << shift);
>         base = 0x72800000;  /* MOVK */
>     } while (value != 0);
> 
> 
> Since we go through the loop at least once, we emit the movz for zero input. No need for any extra tests.  And using ctz we can iterate fewer times.

Of course, doh. I'll make use of do..while. 

Thanks,

Claudio