Re: [PATCH] subreg: Add -fsplit-wide-types-early (PR88233)

[Richard Biener <richard.guenther@gmail.com>]

On Sun, Jul 7, 2019 at 7:12 PM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> 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.

Do you by chance have a (target specific) testcase you can add?

The docs should mention that the new option doesn't have any effect
unless -fsplit-wide-types is enabled.

Otherwise OK.
Richard.

>
> 2019-07-07  Segher Boessenkool  <segher@kernel.crashing.org>
>
>         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.
>
> ---
>  gcc/common.opt                           |  4 +++
>  gcc/common/config/rs6000/rs6000-common.c |  2 ++
>  gcc/doc/invoke.texi                      |  8 +++++-
>  gcc/lower-subreg.c                       | 46 +++++++++++++++++++++++++++++++-
>  gcc/passes.def                           |  3 ++-
>  gcc/tree-pass.h                          |  3 ++-
>  6 files changed, 62 insertions(+), 4 deletions(-)
>
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 41514df..b998b25 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -2430,6 +2430,10 @@ fsplit-wide-types
>  Common Report Var(flag_split_wide_types) Optimization
>  Split wide types into independent registers.
>
> +fsplit-wide-types-early
> +Common Report Var(flag_split_wide_types_early) Optimization
> +Split wide types into independent registers earlier.
> +
>  fssa-backprop
>  Common Report Var(flag_ssa_backprop) Init(1) Optimization
>  Enable backward propagation of use properties at the SSA level.
> diff --git a/gcc/common/config/rs6000/rs6000-common.c b/gcc/common/config/rs6000/rs6000-common.c
> index 9857b54..4b0c205 100644
> --- a/gcc/common/config/rs6000/rs6000-common.c
> +++ b/gcc/common/config/rs6000/rs6000-common.c
> @@ -31,6 +31,8 @@
>  /* Implement TARGET_OPTION_OPTIMIZATION_TABLE.  */
>  static const struct default_options rs6000_option_optimization_table[] =
>    {
> +    /* Split multi-word types early.  */
> +    { OPT_LEVELS_ALL, OPT_fsplit_wide_types_early, NULL, 1 },
>      /* Enable -fsched-pressure for first pass instruction scheduling.  */
>      { OPT_LEVELS_1_PLUS, OPT_fsched_pressure, NULL, 1 },
>      { OPT_LEVELS_NONE, 0, NULL, 0 }
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 73d16b5..6349d4c 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -467,7 +467,7 @@ Objective-C and Objective-C++ Dialects}.
>  -fsignaling-nans @gol
>  -fsingle-precision-constant  -fsplit-ivs-in-unroller  -fsplit-loops@gol
>  -fsplit-paths @gol
> --fsplit-wide-types  -fssa-backprop  -fssa-phiopt @gol
> +-fsplit-wide-types  -fsplit-wide-types-early  -fssa-backprop  -fssa-phiopt @gol
>  -fstdarg-opt  -fstore-merging  -fstrict-aliasing @gol
>  -fthread-jumps  -ftracer  -ftree-bit-ccp @gol
>  -ftree-builtin-call-dce  -ftree-ccp  -ftree-ch @gol
> @@ -8731,6 +8731,12 @@ but may make debugging more difficult.
>  Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
>  @option{-Os}.
>
> +@item -fsplit-wide-types-early
> +@opindex fsplit-wide-types-early
> +Fully split wide types early, instead of very late.
> +
> +This is the default on some targets.
> +
>  @item -fcse-follow-jumps
>  @opindex fcse-follow-jumps
>  In common subexpression elimination (CSE), scan through jump instructions
> diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c
> index 4f68a73..e1418e5 100644
> --- a/gcc/lower-subreg.c
> +++ b/gcc/lower-subreg.c
> @@ -1801,7 +1801,8 @@ public:
>    {}
>
>    /* opt_pass methods: */
> -  virtual bool gate (function *) { return flag_split_wide_types != 0; }
> +  virtual bool gate (function *) { return flag_split_wide_types
> +                                         && flag_split_wide_types_early; }
>    virtual unsigned int execute (function *)
>      {
>        decompose_multiword_subregs (true);
> @@ -1817,3 +1818,46 @@ make_pass_lower_subreg2 (gcc::context *ctxt)
>  {
>    return new pass_lower_subreg2 (ctxt);
>  }
> +
> +/* Implement third lower subreg pass.  */
> +
> +namespace {
> +
> +const pass_data pass_data_lower_subreg3 =
> +{
> +  RTL_PASS, /* type */
> +  "subreg3", /* name */
> +  OPTGROUP_NONE, /* optinfo_flags */
> +  TV_LOWER_SUBREG, /* tv_id */
> +  0, /* properties_required */
> +  0, /* properties_provided */
> +  0, /* properties_destroyed */
> +  0, /* todo_flags_start */
> +  TODO_df_finish, /* todo_flags_finish */
> +};
> +
> +class pass_lower_subreg3 : public rtl_opt_pass
> +{
> +public:
> +  pass_lower_subreg3 (gcc::context *ctxt)
> +    : rtl_opt_pass (pass_data_lower_subreg3, ctxt)
> +  {}
> +
> +  /* opt_pass methods: */
> +  virtual bool gate (function *) { return flag_split_wide_types
> +                                         && !flag_split_wide_types_early; }
> +  virtual unsigned int execute (function *)
> +    {
> +      decompose_multiword_subregs (true);
> +      return 0;
> +    }
> +
> +}; // class pass_lower_subreg3
> +
> +} // anon namespace
> +
> +rtl_opt_pass *
> +make_pass_lower_subreg3 (gcc::context *ctxt)
> +{
> +  return new pass_lower_subreg3 (ctxt);
> +}
> diff --git a/gcc/passes.def b/gcc/passes.def
> index 9a5b0cd..1a7fd14 100644
> --- a/gcc/passes.def
> +++ b/gcc/passes.def
> @@ -427,6 +427,7 @@ along with GCC; see the file COPYING3.  If not see
>           NEXT_PASS (pass_rtl_doloop);
>           NEXT_PASS (pass_rtl_loop_done);
>        POP_INSERT_PASSES ()
> +      NEXT_PASS (pass_lower_subreg2);
>        NEXT_PASS (pass_web);
>        NEXT_PASS (pass_rtl_cprop);
>        NEXT_PASS (pass_cse2);
> @@ -440,7 +441,7 @@ along with GCC; see the file COPYING3.  If not see
>        NEXT_PASS (pass_partition_blocks);
>        NEXT_PASS (pass_outof_cfg_layout_mode);
>        NEXT_PASS (pass_split_all_insns);
> -      NEXT_PASS (pass_lower_subreg2);
> +      NEXT_PASS (pass_lower_subreg3);
>        NEXT_PASS (pass_df_initialize_no_opt);
>        NEXT_PASS (pass_stack_ptr_mod);
>        NEXT_PASS (pass_mode_switching);
> diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
> index b27dbdd..7b83293 100644
> --- a/gcc/tree-pass.h
> +++ b/gcc/tree-pass.h
> @@ -552,6 +552,7 @@ extern rtl_opt_pass *make_pass_rtl_unroll_loops (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_rtl_doloop (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_rtl_loop_done (gcc::context *ctxt);
>
> +extern rtl_opt_pass *make_pass_lower_subreg2 (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_web (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_cse2 (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_df_initialize_opt (gcc::context *ctxt);
> @@ -567,7 +568,7 @@ extern rtl_opt_pass *make_pass_partition_blocks (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_match_asm_constraints (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_split_all_insns (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_fast_rtl_byte_dce (gcc::context *ctxt);
> -extern rtl_opt_pass *make_pass_lower_subreg2 (gcc::context *ctxt);
> +extern rtl_opt_pass *make_pass_lower_subreg3 (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_mode_switching (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_sms (gcc::context *ctxt);
>  extern rtl_opt_pass *make_pass_sched (gcc::context *ctxt);
> --
> 1.8.3.1
>