[Bug middle-end/42371] dead code not eliminated during folding with whole-program

["hubicka at ucw dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42371

--- Comment #15 from Jan Hubicka <hubicka at ucw dot cz> 2013-01-19 21:48:12 UTC ---
> Clearing of address-taken does not work:
> 
> two/1 (two) @0x7fafc0e29818
>   Type: function
>   Visibility: prevailing_def_ironly
>   Address is taken.
>   References:
>   Referring: main/3 (addr)
>   Availability: available
>   Function flags: analyzed body finalized
>   Called by:
>   Calls:
> 
> that is, we do not re-compute address-taken after IPA inline transform stage
> and thus do not reclaim indirectly inlined functions that we no longer need.

We can't recompute here because inlining transform happens during the final
compilation stage, so the functions are already beging output to the assembly.

IPA-prop needs to realize that indirect inlining is going to optimize out the
address operation and remove the reference.  I assume this is not too hard to
implement - we only need to record when the function parameter is used _only_
of the stuff represented by jump functions and indirect edges. I was trying
to convince Martin to implement this for a while :)

Virtual functions are ven harder than indirect calls since we need to figure
out
the vtable will become unreachable at the IPA stage.

Honza