public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug middle-end/107115] New: Wrong codegen from TBAA under stores that change effective type?
@ 2022-10-01 20:00 bugdal at aerifal dot cx
  2022-10-01 23:34 ` [Bug rtl-optimization/107115] " pinskia at gcc dot gnu.org
                   ` (13 more replies)
  0 siblings, 14 replies; 15+ messages in thread
From: bugdal at aerifal dot cx @ 2022-10-01 20:00 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107115

            Bug ID: 107115
           Summary: Wrong codegen from TBAA under stores that change
                    effective type?
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugdal at aerifal dot cx
  Target Milestone: ---

Created attachment 53648
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53648&action=edit
original test case by supercat

The attached test case is from user supercat on Stack Overflow (original
source:
https://stackoverflow.com/questions/42178179/will-casting-around-sockaddr-storage-and-sockaddr-in-break-strict-aliasing/42178347?noredirect=1#comment130510083_42178347,
https://godbolt.org/z/jfv1Ge6v4) and demonstrates what appears to be wrong TBAA
optimization on an object with allocated storage whose effective type changes
under stores. It was first presented as another example of this kind of problem
alongside the example that became
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107107, but it seems likely that
the root cause is distinct.

Reportedly clang/LLVM also transforms this example wrong.

On 64-bit targets, the test program outputs 2/1 with optimization levels that
enable -fstrict-aliasing. The expected output is 2/2. Using
-fno-strict-aliasing fixes it.

^ permalink raw reply	[flat|nested] 15+ messages in thread

end of thread, other threads:[~2022-12-27 22:21 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-10-01 20:00 [Bug middle-end/107115] New: Wrong codegen from TBAA under stores that change effective type? bugdal at aerifal dot cx
2022-10-01 23:34 ` [Bug rtl-optimization/107115] " pinskia at gcc dot gnu.org
2022-10-01 23:51 ` [Bug middle-end/107115] " pinskia at gcc dot gnu.org
2022-10-06  9:44 ` rguenth at gcc dot gnu.org
2022-10-06 12:20 ` cvs-commit at gcc dot gnu.org
2022-10-06 12:24 ` rguenth at gcc dot gnu.org
2022-10-06 15:19 ` amonakov at gcc dot gnu.org
2022-10-06 15:32 ` jakub at gcc dot gnu.org
2022-10-06 15:39 ` amonakov at gcc dot gnu.org
2022-10-06 19:04 ` pinskia at gcc dot gnu.org
2022-10-07  7:41 ` rguenth at gcc dot gnu.org
2022-10-07  7:44 ` rguenth at gcc dot gnu.org
2022-10-07 13:19 ` amonakov at gcc dot gnu.org
2022-12-27 22:19 ` gabravier at gmail dot com
2022-12-27 22:21 ` gabravier at gmail dot com

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).