[Bug ipa/65270] [5 regression] ICF needs to match TYPE attributes on memory accesses

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65270

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #9 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Lets reopen this.  I agree with other type flags - they seem safe except for
TYPE_ATTRIBUTES of functions I will add compare of today.

> No.  But you can't compare restrict qualification by looking at a memory
> reference pair from function A and function B.  You'd have to compare
> all data dependences somehow.
>
> You could get some cases by comparing function parameter types specially
> (but global vars also have an issue, as well as decl-by-reference
> aggregate parameters).

Would it be enough to
 - require match on arguments/return value types (that should handle function
parameters as well as 
 - require match on all global variable types

> It seems to me that ICF isn't quite ready for prime time.  Let's disable
> it by default for now, ok?

I also read the discussion on IRC and discussed with Jeff.
ICF has triggered interesting issues in alias/thunks areas. For a first time we
output a lot of non-MI thunks on main targets and expand_thunk was getting
things wrong in a nasty ways.  ICF also produce a lot of aliases and excercise
symbol table code otherwise rarely used. Here I think it is valuable we fixed
those bugs that were semi-latent for years.  I believe we are approaching
steady state - at the moment we do not have any other ICF related PR open. Jeff
suggested to wait 48 hours.

This PR is a result of my code audit I did over weekend. I fully leave the
decision with you. I agree ICF is causing a lot of issues late in release and
disabling it is a safe option. On the other hand I would be happy to work to
get it fixed and working - it is quite useful optimization.