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From: "lin1.hu at intel dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/114700] New: Front-end optimization generates wrong code with -ftrapv. Date: Fri, 12 Apr 2024 02:22:27 +0000 [thread overview] Message-ID: <bug-114700-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114700 Bug ID: 114700 Summary: Front-end optimization generates wrong code with -ftrapv. Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: lin1.hu at intel dot com Target Milestone: --- We test GCC vs Clang with -ftrapv, and test is z = c - y - c + a + y - b; https://godbolt.org/z/EW1xTsazG We think the clang is right, the overflow judgment should be performed after each operation. But the front-end generates a - b directly, looks like there's a bug in the front-end's handling of -ftrapv. -ftrapv This option generates traps for signed overflow on addition, subtraction, multiplication operations. The options -ftrapv and -fwrapv override each other, so using -ftrapv -fwrapv on the command-line results in -fwrapv being effective. Note that only active options override, so using -ftrapv -fwrapv -fno-wrapv on the command-line results in -ftrapv being effective. We have another question, we found the front-end won't optimize z = c - y + a - c, while z = c - y - c + a will, is this for any particular reason or is it a bug?
next reply other threads:[~2024-04-12 2:22 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-12 2:22 lin1.hu at intel dot com [this message] 2024-04-12 2:34 ` [Bug middle-end/114700] " pinskia at gcc dot gnu.org 2024-04-12 2:47 ` lin1.hu at intel dot com 2024-04-12 2:47 ` lin1.hu at intel dot com 2024-04-12 3:21 ` pinskia at gcc dot gnu.org 2024-04-12 3:26 ` pinskia at gcc dot gnu.org 2024-04-12 3:35 ` pinskia at gcc dot gnu.org 2024-04-12 3:53 ` lin1.hu at intel dot com 2024-04-12 3:56 ` lin1.hu at intel dot com 2024-04-12 5:56 ` rguenth at gcc dot gnu.org 2024-04-12 6:33 ` [Bug middle-end/114700] Front-end optimization generates wrong code with -fsanitize=undefined xry111 at gcc dot gnu.org 2024-04-12 6:44 ` lin1.hu at intel dot com 2024-04-12 7:12 ` lin1.hu at intel dot com 2024-04-12 7:14 ` xry111 at gcc dot gnu.org 2024-04-12 8:51 ` lin1.hu at intel dot com 2024-04-12 10:15 ` [Bug middle-end/114700] middle-end " jakub at gcc dot gnu.org 2024-04-12 10:25 ` jakub at gcc dot gnu.org 2024-04-15 3:43 ` [Bug middle-end/114700] middle-end optimization generates causes -fsanitize=undefined not to happen in some cases lin1.hu at intel dot com 2024-04-15 6:49 ` jakub at gcc dot gnu.org 2024-04-15 7:44 ` lin1.hu at intel dot com 2024-04-17 1:50 ` lin1.hu at intel dot com
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