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Thread-Topic: Why does this unrolled function write to the stack? 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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: 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 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: VE1PR06MB7054.eurprd06.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 648c3909-d514-4d51-73bb-08db0a05b26f X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Feb 2023 18:52:58.7507 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f85626cb-0da8-49d3-aa58-64ef678ef01a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: BC7AgSSAwTdROXkqQxcBYCxIdmUSMDgOxDttOSOw9CeI5YIsUvMTEYrbxvbcArJZCZ28tTB8OjAWPfRu6R41mA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR06MB5373 X-Spam-Level: * X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Thanks for the help investigating, both of you!=0A= =0A= > It seems to be a regression between gcc 10 and gcc 11 (discovered by=0A= > changing the compiler on godbolt.org). With gcc 11 onwards, the=0A= > compiler seems to be using the stack to combine two 4-byte elements at a= =0A= > time into a single 8-byte element. It's easy to see the effect by=0A= > changing the loop size to 2.=0A= =0A= I gave this a bisect, and it looks like the commit that caused it is this o= ne:=0A= =0A= commit 33c0f246f799b7403171e97f31276a8feddd05c9=0A= Author: Richard Biener =0A= Date: Fri Oct 30 11:26:18 2020 +0100=0A= =0A= tree-optimization/97626 - handle SCCs properly in SLP stmt analysis=0A= =0A= The details of how this ties back to the behavior we're seeing go far=0A= above my head, unfortunately.=0A= =0A= I'll go ahead and file a bug on the tracker.=0A= =0A= Thanks again,=0A= Gaelan=0A= PS Apologies for the horrendous wrapping in my previous email! I'm=0A= using webmail because my normal machine is in repair, and list etiquette=0A= totally slipped my mind.=