[Bug tree-optimization/90905] missing -Wreturn-local-addr returning a local std::string::c_str()

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90905

--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
> compiling both functions in the samne translatin unit suppresses the warning for f0.

It is quite common for extra code to change inlining decisions. You still get
the warning at -O3.

> const char *p = "def";

Did you mean to write

const char * const p = "def";

(which does warn)? Otherwise, the compiler has no way to know this is a short
string, so we end up with a function that returns either the address of a local
variable or a pointer to deleted memory (although we don't have a nice PHI like
that, even with -std=c++2a to disable extern templates, probably some
suboptimal aliasing analysis).