[Bug rtl-optimization/88233] combine fails to merge insns leaving unneeded reg copies

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88233

--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Mon Jul  8 17:35:12 2019
New Revision: 273240

URL: https://gcc.gnu.org/viewcvs?rev=273240&root=gcc&view=rev
Log:
subreg: Add -fsplit-wide-types-early (PR88233)

Currently the second lower-subreg pass is run right before RA.  This
is much too late to be very useful.  At least for targets that do not
have RTL patterns for operations on multi-register modes it is a lot
better to split patterns earlier, before combine and all related
passes.

This adds an option -fsplit-wide-types-early that does that, and
enables it by default for rs6000.


        PR rtl-optimization/88233
        * common.opt (fsplit-wide-types-early): New option.
        * common/config/rs6000/rs6000-common.c
        (rs6000_option_optimization_table): Add OPT_fsplit_wide_types_early for
        OPT_LEVELS_ALL.
        * doc/invoke.texi (Optimization Options): Add -fsplit-wide-types-early.
        * lower-subreg.c (pass_lower_subreg2::gate): Add test for
        flag_split_wide_types_early.
        (pass_data_lower_subreg3): New.
        (pass_lower_subreg3): New.
        (make_pass_lower_subreg3): New.
        * passes.def (pass_lower_subreg2): Move after the loop passes.
        (pass_lower_subreg3): New, inserted where pass_lower_subreg2 was.
        * tree-pass.h (make_pass_lower_subreg2): Move up, to its new place in
        the pass pipeline; its previous place is taken by ...
        (make_pass_lower_subreg3): ... this.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/common.opt
    trunk/gcc/common/config/rs6000/rs6000-common.c
    trunk/gcc/doc/invoke.texi
    trunk/gcc/lower-subreg.c
    trunk/gcc/passes.def
    trunk/gcc/tree-pass.h