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* [Bug c++/105884] New: A possible optimization bug when uint64_t is used with -O2/-O3.
@ 2022-06-08 8:49 zhonghao at pku dot org.cn
2022-06-08 8:54 ` [Bug c++/105884] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: zhonghao at pku dot org.cn @ 2022-06-08 8:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105884
Bug ID: 105884
Summary: A possible optimization bug when uint64_t is used with
-O2/-O3.
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: zhonghao at pku dot org.cn
Target Milestone: ---
zapret is a tool to bypass network blocking:
https://github.com/bol-van/zapret/blob/master/docs/readme.eng.md
I notice that its programmers complain an optimization bug. This bug is
triggered when gcc optimizes uint64_t. The commit is
https://github.com/bol-van/zapret/commit/9402cd2cf0a16352a3401f7bce1a894bf131138b
Please check the problem.
^ permalink raw reply [flat|nested] 4+ messages in thread* [Bug c++/105884] A possible optimization bug when uint64_t is used with -O2/-O3. 2022-06-08 8:49 [Bug c++/105884] New: A possible optimization bug when uint64_t is used with -O2/-O3 zhonghao at pku dot org.cn @ 2022-06-08 8:54 ` pinskia at gcc dot gnu.org 2022-06-08 9:35 ` redi at gcc dot gnu.org 2022-06-08 9:41 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-06-08 8:54 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105884 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- I am 99% sure this is an aliasing issue with the code. Try -fno-strict-aliasing. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/105884] A possible optimization bug when uint64_t is used with -O2/-O3. 2022-06-08 8:49 [Bug c++/105884] New: A possible optimization bug when uint64_t is used with -O2/-O3 zhonghao at pku dot org.cn 2022-06-08 8:54 ` [Bug c++/105884] " pinskia at gcc dot gnu.org @ 2022-06-08 9:35 ` redi at gcc dot gnu.org 2022-06-08 9:41 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2022-06-08 9:35 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105884 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |INVALID Status|UNCONFIRMED |RESOLVED --- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- Definitely an aliasing bug: ((uint64_t*)result->s6_addr)[0] = ((uint64_t*)a->s6_addr)[0] & ((uint64_t*)b->s6_addr)[0]; ((uint64_t*)result->s6_addr)[1] = ((uint64_t*)a->s6_addr)[1] & ((uint64_t*)b->s6_addr)[1]; Even their "fix" to use uint32_t instead is wrong. With glibc the s6_addr array has type uint8_t[16] so there are no uint64_t (or uint32_t) objects there. With _GNU_SOURCE or _DEFAULT_SOURCE (formerly _BSD_SOURCE) defined, there is a s6_addr32 member which can be used to type-pun the s6_addr array as 32-bit values. The portable solution is to memcpy from s6_addr to uint64_t[2], perform the bitwise AND ops on the uint64_t objects, and then memcpy back to s6_addr. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/105884] A possible optimization bug when uint64_t is used with -O2/-O3. 2022-06-08 8:49 [Bug c++/105884] New: A possible optimization bug when uint64_t is used with -O2/-O3 zhonghao at pku dot org.cn 2022-06-08 8:54 ` [Bug c++/105884] " pinskia at gcc dot gnu.org 2022-06-08 9:35 ` redi at gcc dot gnu.org @ 2022-06-08 9:41 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2022-06-08 9:41 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105884 --- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- I commented upstream: https://github.com/bol-van/zapret/commit/9402cd2cf0a16352a3401f7bce1a894bf131138b#r75598628 ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-06-08 9:41 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-06-08 8:49 [Bug c++/105884] New: A possible optimization bug when uint64_t is used with -O2/-O3 zhonghao at pku dot org.cn 2022-06-08 8:54 ` [Bug c++/105884] " pinskia at gcc dot gnu.org 2022-06-08 9:35 ` redi at gcc dot gnu.org 2022-06-08 9:41 ` redi at gcc dot gnu.org
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