[Bug tree-optimization/42970] Missed unused function return value elimination

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42970

--- Comment #7 from Martin Jambor <jamborm at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #6)
> 
> Stage 1 has opened again.

And therefore I have submitted a cleaned-up version for review:

https://gcc.gnu.org/ml/gcc-patches/2019-05/msg00472.html