[Bug middle-end/110292] undefined value due to strict aliasing without warning

["xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110292

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #6 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Yann Droneaud from comment #5)
> Hi,
> 
> Thanks a lot for the quick analysis of my issue.
> 
> (In reply to Andrew Pinski from comment #4)
> > Note -Wstrict-aliasing=1 actually does warn:
> 
> OK, and -Wall enables -Wstrict-aliasing which defaults to
> -Wstrict-aliasing=3,
> I'm sorry I haven't tried to use lower values ...

The problem is -Wstrict-aliasing=1 may produce many false positives, as it's
documented.

> https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstrict-
> aliasing
> 
> (In reply to Andrew Pinski from comment #2)
> > aliasing violations are known not to be warned about nor have a runtime
> > sanitizer either.
> 
> Is there any other tool that would reliably detect such issues ?

Such issues are obviously impossible to be detected reliably at compile time
(because doing so will need to solve the halting problem).  At runtime LLVM
guys are developing a type sanitizer:
https://discourse.llvm.org/t/reviving-typesanitizer-a-sanitizer-to-catch-type-based-aliasing-violations