[Bug c++/79658] [-Wuninitialized] referencing uninitialized field of POD struct should warn

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79658

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
For your testcase foo () is quickly optimized to nothing given ef is unused. 
For -O0 we only warn before inlining.