[Bug tree-optimization/25290] PHI-OPT could be rewritten so that is uses match

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25290

--- Comment #22 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Without load/store handling, here are the following optimizations that either
can move to match.pd already or need some extra work to do it:

* value_replacement: need to handle !single_non_singleton_phi_for_edges case
and more than one feeder statement (2 max according to the current definition)
* cond_removal_in_popcount_clz_ctz_pattern: need 2 feeder statements and
builtin call handling for feeder statements


* two_value_replacement: recored as PR 100958, it can move already
* abs_replacement: needs PROP_gimple_lswitch so we don't change if statements
early enough
** I think majority of the abs handling is already in match.pd.
* minmax_replacement: has some handling of comparisions which might not be in
the match.pd patterns already.  needs PROP_gimple_lswitch also.
** The handling of:
         if (a <= u)
           b = MAX (a, d);
         x = PHI <b, u>
   needs to moved too.


For the ones which cannot move
* factor_out_conditional_conversion: will never move, though it needs
improvement and moved already (PR 56223 and PR 13563)
* spaceship_replacement: cannot move to match.pd depends on use afterwards
which is not hard to deal with in a match pattern.