https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89561
bugsthecode at mail dot ru changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|WONTFIX |---
--- Comment #6 from bugsthecode at mail dot ru ---
(In reply to Richard Biener from comment #5)
> Note that iff GCC could easily see "what you want" and see that some
> undefined behavior rule contradicts this then from a QOI perspective GCC
> already tries
> to do what you want.
What does "QOI" mean? And no, there is no perspective where GCC tries to do
what I want, unless it's a perspective with brain damage. I'm not talking even
about "legacy" option, an "error" option is unavailable as well. Only
"generate-crap" is available, and happens more and more often.
> The difficult thing is to detect what you want (from
> inside generic analysis infrastructure).
You literally have source code to see what I want. I wrote it there. Maybe not
ideally and without bugs, but it is there.
That's definitely not what user wants:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89218
That's miscompilation by gcc. User didn't request a crash there. And gcc-7
didn't generate such crap. But it's not recognized as regression because it's
swept under the "we can generate any crap when undefined behaviour is
encountered" crap.
> For example GCC will not misoptimize
>
> int i;
>
> int main() { *(float *)&i = 0.0; return i; }
>
> even if it could (because type-based alias rules make the code undefined)
> because it sees the must-alias.
>
Are you going to fix this case to generate crap as well in next gcc release?
> That is, -fundefined-behavior=XYZ is impossible besides making all undefined
> behavior implementation-defined (there are many options to individually
> control
> such thing already, like -fwrapv for example).
Ok, there's huge amount of warning flags, but there's also -Wall and -Wextra to
enable a lot of them at once. And there is -Werror to turn all of them into
errors. Is there a global option for undefined behaviour configuration? None I
know of.
And what's so bad with changing undefined behaviour into implementation-defined
behaviour? Better than potential CVE in my book.
Why such option as -fwrapv even exists? Why not use safe defaults, and add
options like -funsafe-fast-no-wrapv which would disable such behaviour but
potentially make binary faster? -O2 used to be safe recommended optimization
level, but now it generates a lot of crap. Maybe fast crap, but still a pile of
vulnerable crashing crap.
