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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/108140] tzcnt gives different result in debug vs release Date: Fri, 16 Dec 2022 08:28:18 +0000 [thread overview] Message-ID: <bug-108140-4-YCgpBDSiNe@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-108140-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108140 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jakub at gcc dot gnu.org --- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> --- If you call __builtin_ctzll with argument 0, it is undefined behavior, you can't make any assumptions, regardless what instructions you assume will be used or are actually used. If you write your code as x ? __builtin_ctzll (x) : 64 or similar, GCC if it uses an instruction that guarantees that result for 0 might actually fold it back into just that instruction unconditionally.
next prev parent reply other threads:[~2022-12-16 8:28 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-12-16 8:18 [Bug c/108140] New: " levo.delellis at gmail dot com 2022-12-16 8:28 ` jakub at gcc dot gnu.org [this message] 2022-12-16 8:29 ` [Bug c/108140] " jakub at gcc dot gnu.org 2022-12-16 8:45 ` levo.delellis at gmail dot com 2022-12-16 9:35 ` [Bug middle-end/108140] ICE expanding __rbit amonakov at gcc dot gnu.org 2022-12-16 11:55 ` ktkachov at gcc dot gnu.org 2022-12-19 11:19 ` [Bug target/108140] " cvs-commit at gcc dot gnu.org 2023-01-10 10:26 ` cvs-commit at gcc dot gnu.org 2023-05-08 12:26 ` rguenth at gcc dot gnu.org 2023-05-09 9:04 ` ktkachov at gcc dot gnu.org
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