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Tue, 25 Jul 2017 21:25:46 +0000 Received: from DB6PR0801MB2053.eurprd08.prod.outlook.com ([fe80::cd9d:80f1:82d8:5181]) by DB6PR0801MB2053.eurprd08.prod.outlook.com ([fe80::cd9d:80f1:82d8:5181%18]) with mapi id 15.01.1282.020; Tue, 25 Jul 2017 21:25:46 +0000 From: Wilco Dijkstra To: Jeff Law , GCC Patches CC: nd Subject: Re: [PATCH] Fix PR46932: Block auto increment on frame pointer Date: Tue, 25 Jul 2017 21:25:00 -0000 Message-ID: References: ,<27a1b18b-a698-f50d-f026-1dc956e3c673@redhat.com> In-Reply-To: <27a1b18b-a698-f50d-f026-1dc956e3c673@redhat.com> authentication-results: spf=none (sender IP is ) smtp.mailfrom=Wilco.Dijkstra@arm.com; x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DB6PR0801MB2055;7: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 x-ms-office365-filtering-correlation-id: e42829bf-9971-4398-e537-08d4d3a3b6c9 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(300000500095)(300135000095)(300000501095)(300135300095)(22001)(300000502095)(300135100095)(2017030254075)(48565401081)(300000503095)(300135400095)(2017052603031)(201703131423075)(201703031133081)(300000504095)(300135200095)(300000505095)(300135600095)(300000506095)(300135500095);SRVR:DB6PR0801MB2055; 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received-spf: None (protection.outlook.com: arm.com does not designate permitted sender hosts) spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-originalarrivaltime: 25 Jul 2017 21:25:46.3866 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB6PR0801MB2055 X-SW-Source: 2017-07/txt/msg01611.txt.bz2 Jeff Law wrote: > My only concern here would be cases where we don't end up eliminating FP > to SP.=A0 But I'd think it's unlikely that we'd have enough auto-inc > opportunities on the frame pointer for it to matter much anyway. What kind of case are you thinking of? Whether it is SP or FP doesn't matte= r, we cannot copy propagate the pointer: add x1, fp, 32 strb w0, [x1, -1]! =20=20=20=20 Not even if the elimination offset is zero: mov x1, fp strb w0, [x1, 31]! Basically an independent add is better than the above: strb w0, [fp, 31] add x1, fp, 31 I think the phase is still overly aggressive and there are more cases where= it=20 doesn't make sense to use auto increment. For example you will extra moves just like the 2nd case above when it's not the last use of the source. Wilco