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Re: [AArch64][PR65139] use clobber with match_scratch for aarch64_lshr_sisd_or_int_<mode>3
- From: Richard Earnshaw <Richard dot Earnshaw at foss dot arm dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Kugan <kugan dot vivekanandarajah at linaro dot org>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>, James Greenhalgh <James dot Greenhalgh at arm dot com>, Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>
- Date: Sat, 18 Apr 2015 18:21:56 +0100
- Subject: Re: [AArch64][PR65139] use clobber with match_scratch for aarch64_lshr_sisd_or_int_<mode>3
- Authentication-results: sourceware.org; auth=none
- References: <552D897C dot 2040207 at linaro dot org> <552E571C dot 3000306 at foss dot arm dot com> <20150415123202 dot GW1725 at tucnak dot redhat dot com> <552EE5CC dot 9040703 at linaro dot org> <20150415223248 dot GZ1725 at tucnak dot redhat dot com> <552EED9F dot 3060901 at linaro dot org> <55326514 dot 8080008 at foss dot arm dot com> <20150418151309 dot GY1725 at tucnak dot redhat dot com>
On 18/04/15 16:13, Jakub Jelinek wrote:
> On Sat, Apr 18, 2015 at 03:07:16PM +0100, Richard Earnshaw wrote:
>> You need to ensure that your scratch register cannot overlap op1, since
>> the scratch is written before op1 is read.
>
> - (clobber (match_scratch:QI 3 "=X,w,X"))]
> + (clobber (match_scratch:QI 3 "=X,&w,X"))]
>
> incremental diff should ensure that, right?
>
> Jakub
>
Sorry, where in the patch is that hunk?
I see just:
+ (clobber (match_scratch:QI 3 "=X,w,X"))]
And why would early clobbering the scratch be notably better than the
original?
R.