[Bug c/82100] gcc does not warn about code that is unreachable due to conflicting conditions [subset of reviving -Wunreachable-code]

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82100

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The FEs don't do static analysis that could detect this and it's incredibly
hard to do this during optimization given we'd have to track all instances of
code
(think of inlining, jump threading duplicating blocks, unrolling, etc.).

It might be possible to funnel this kind of warning into one of the very
early passes (but even those see inlines).