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From: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/110237] gcc.dg/torture/pr58955-2.c is miscompiled by RTL scheduling after reload Date: Mon, 26 Jun 2023 08:54:15 +0000 [thread overview] Message-ID: <bug-110237-4-sKR0uRspZJ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-110237-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110237 --- Comment #16 from Alexander Monakov <amonakov at gcc dot gnu.org> --- (In reply to rguenther@suse.de from comment #14) > vectors of T and scalar T interoperate TBAA wise. What we disambiguate is > > int a[2]; > > int foo(int *p) > { > a[0] = 1; > *(v4si *)p = {0,0,0,0}; > return a[0]; > } > > because the V4SI vector store is too large for the a[] object. That > doesn't even use TBAA (it works with -fno-strict-aliasing just fine). Thank you for the example. If we do the same for vector loads, that's a footgun for users who use vector loads to access small objects: // alignment to 16 is ensured externally extern int a[2]; int foo() { a[0] = 1; __v4si v = (__attribute__((may_alias)) __v4si *) &a; // mask out extra elements in v and continue ... } This is a benign data race on data that follows 'a' in the address space, but otherwise should be a valid and useful technique. > If the v4si store is masked we cannot do this anymore, but the IL > we seed the alias oracle with doesn't know the store is partial. > The only way to "fix" it is to take away all of the information from it. But that won't fix the trapping issue? I think we need a distinct RTX for memory accesses where hardware does fault suppression for masked-out elements.
next prev parent reply other threads:[~2023-06-26 8:54 UTC|newest] Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-06-13 13:50 [Bug rtl-optimization/110237] New: " rguenth at gcc dot gnu.org 2023-06-14 11:02 ` [Bug rtl-optimization/110237] " amonakov at gcc dot gnu.org 2023-06-14 12:09 ` rguenth at gcc dot gnu.org 2023-06-20 9:52 ` rguenth at gcc dot gnu.org 2023-06-20 11:35 ` crazylht at gmail dot com 2023-06-20 12:20 ` rguenther at suse dot de 2023-06-20 16:05 ` crazylht at gmail dot com 2023-06-21 5:48 ` crazylht at gmail dot com 2023-06-21 7:33 ` rguenth at gcc dot gnu.org 2023-06-25 4:06 ` crazylht at gmail dot com 2023-06-26 7:41 ` rguenther at suse dot de 2023-06-26 7:58 ` amonakov at gcc dot gnu.org 2023-06-26 8:07 ` rguenther at suse dot de 2023-06-26 8:22 ` amonakov at gcc dot gnu.org 2023-06-26 8:35 ` rguenther at suse dot de 2023-06-26 8:44 ` crazylht at gmail dot com 2023-06-26 8:54 ` amonakov at gcc dot gnu.org [this message] 2023-06-26 11:14 ` rguenther at suse dot de 2023-06-26 18:19 ` amonakov at gcc dot gnu.org 2023-06-27 6:53 ` rguenther at suse dot de 2023-06-27 7:30 ` cvs-commit at gcc dot gnu.org 2023-06-27 9:50 ` amonakov at gcc dot gnu.org 2023-06-27 10:03 ` rguenther at suse dot de 2023-06-29 1:27 ` cvs-commit at gcc dot gnu.org 2023-06-29 1:28 ` cvs-commit at gcc dot gnu.org 2023-06-29 1:29 ` cvs-commit at gcc dot gnu.org 2023-11-27 12:39 ` rdapp at gcc dot gnu.org 2023-11-29 12:26 ` cvs-commit at gcc dot gnu.org 2023-11-29 12:27 ` rguenth at gcc dot gnu.org
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