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Lu" Cc: Haochen Jiang , wwwhhhyyy , binutils@sourceware.org References: <20221014091248.4920-1-haochen.jiang@intel.com> <20221014091248.4920-2-haochen.jiang@intel.com> <863655db-f202-477f-c638-00773c25886c@suse.com> <6d3a01b1-2576-f329-0a36-486526c0b03b@suse.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR3P281CA0143.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:95::6) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AS8PR04MB9112:EE_ X-MS-Office365-Filtering-Correlation-Id: 31dfcd24-cfca-4b23-e1cb-08dab1974ff3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:VE1PR04MB6560.eurprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(366004)(136003)(346002)(39860400002)(376002)(396003)(451199015)(36756003)(31686004)(31696002)(86362001)(5660300002)(2906002)(38100700002)(2616005)(186003)(54906003)(6486002)(83380400001)(6506007)(53546011)(316002)(26005)(6916009)(66946007)(478600001)(66556008)(8936002)(66476007)(4326008)(41300700001)(6512007)(8676002)(45980500001)(43740500002);DIR:OUT;SFP:1101; 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Lu wrote: > On Mon, Oct 17, 2022 at 10:33 PM Jan Beulich wrote: >> >> On 18.10.2022 00:23, H.J. Lu wrote: >>> On Sat, Oct 15, 2022 at 11:39 PM Jan Beulich wrote: >>>> >>>> On 14.10.2022 20:10, H.J. Lu wrote: >>>>> On Fri, Oct 14, 2022 at 2:52 AM Jan Beulich wrote: >>>>>> >>>>>> On 14.10.2022 11:12, Haochen Jiang wrote: >>>>>>> From: wwwhhhyyy >>>>>>> >>>>>>> x86: Support Intel AVX-IFMA >>>>>>> >>>>>>> Intel AVX IFMA instructions are marked with CpuVEX_PREFIX, which is >>>>>>> cleared by default. Without {vex} pseudo prefix, Intel IFMA instructions >>>>>>> are encoded with EVEX prefix. {vex} pseudo prefix will turn on VEX >>>>>>> encoding for Intel IFMA instructions. >>>>>> >>>>>> I firmly object to the proliferation of this mis-feature. As expressed >>>>>> before for AVX-VNNI, as long as the user has disabled AVX512 (or >>>>>> respective sub-features thereof), there should be no need to use {vex} in >>>>>> the source code. There's also no reason at all to make the disassembler >>>>>> print {vex} prefixes - we don't do so for any other insns (apart from >>>>>> AVX-VNNI) where an ambiguity exists between their VEX and EVEX encodings >>>>>> (when none of the EVEX-specific features is used). >>>>> >>>>> The {vex} prefix is used with AVX-IFMA instructions so that IFMA instructions >>>>> without a prefix, which are generated by compilers or handwritten, will be >>>>> always encoded with EVEX. >>>> >>>> So again: Why is this necessary when a programmer disabled AVX512? I fully >>>> agree we need to pick the EVEX encoding by default if available, but I see >>>> no reason whatsoever to insist on a {vex} prefix when the EVEX variant is >>>> unavailable anyway. As you said back at the time for AVX-VNNI - this was a >>>> design decision taken at Intel. Which is fine for a draft implementation. >>>> But decisions for an open source project should be taken in the open, and >>>> opinions of others should not simply be put off. >>>> >>> >>> We can discuss how to initialize i.vec_encoding. But it is orthogonal to >>> this patch. >> >> One can view it as orthogonal, yes, but if we change the model then doing >> so before more code and testcases need changing is imo preferable. >> > > We can skip the pseudo VEX prefix check when AVX512F is disabled. Let me see if I can pull ahead the patch I have (right now it's at the end of the 3rd series I have pending, when the 1st one continues to be debated), so the new cases in this series could then come on top. > There should be no testcase changes. Well - existing tests ought it continue to work, yes, but the prefix-less forms then also will want testing. Jan