Re: [PATCH] tree-ssa-loop-ivopts : Add live analysis in regs used in decision making

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

On Wed, Nov 8, 2023 at 4:00 PM Ajit Agarwal <aagarwa1@linux.ibm.com> wrote:
>
> tree-ssa-loop-ivopts : Add live analysis in regs used in decision making.
>
> Add live anaysis in regs used calculation in decision making of
> selecting ivopts candidates.
>
> 2023-11-08  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>
>
> gcc/ChangeLog:
>
>         * tree-ssa-loop-ivopts.cc (get_regs_used): New function.
>         (determine_set_costs): Call to get_regs_used to use live
>         analysis.
> ---
>  gcc/tree-ssa-loop-ivopts.cc | 73 +++++++++++++++++++++++++++++++++++--
>  1 file changed, 70 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
> index c3336603778..e02fe7d434b 100644
> --- a/gcc/tree-ssa-loop-ivopts.cc
> +++ b/gcc/tree-ssa-loop-ivopts.cc
> @@ -6160,6 +6160,68 @@ ivopts_estimate_reg_pressure (struct ivopts_data *data, unsigned n_invs,
>    return cost + n_cands;
>  }
>
> +/* Return regs used based on live-in and liveout of given ssa variables.  */

Please explain how the following code relates to anything like "live
analysis" and
where it uses live-in and live-out.  And what "live-in/out of a given
SSA variable"
should be.

Also explain why you are doing this at all.  The patch doesn't come
with a testcase
or with any other hint that motivated you.

Richard.

> +static unsigned
> +get_regs_used (tree ssa_name)
> +{
> +  unsigned regs_used = 0;
> +  gimple *stmt;
> +  use_operand_p use;
> +  basic_block def_bb = NULL;
> +  imm_use_iterator imm_iter;
> +
> +  stmt = SSA_NAME_DEF_STMT (ssa_name);
> +  if (stmt)
> +    {
> +      def_bb = gimple_bb (stmt);
> +      /* Mark defs in liveout bitmap temporarily.  */
> +      if (def_bb)
> +       regs_used++;
> +    }
> +  else
> +    def_bb = ENTRY_BLOCK_PTR_FOR_FN (cfun);
> +
> +  /* An undefined local variable does not need to be very alive.  */
> +  if (virtual_operand_p (ssa_name)
> +      || ssa_undefined_value_p (ssa_name, false))
> +    return 0;
> +
> +  /* Visit each use of SSA_NAME and if it isn't in the same block as the def,
> +     add it to the list of live on entry blocks.  */
> +  FOR_EACH_IMM_USE_FAST (use, imm_iter, ssa_name)
> +    {
> +      gimple *use_stmt = USE_STMT (use);
> +      basic_block add_block = NULL;
> +
> +      if (gimple_code (use_stmt) == GIMPLE_PHI)
> +       {
> +         /* Uses in PHI's are considered to be live at exit of the SRC block
> +            as this is where a copy would be inserted.  Check to see if it is
> +            defined in that block, or whether its live on entry.  */
> +         int index = PHI_ARG_INDEX_FROM_USE (use);
> +         edge e = gimple_phi_arg_edge (as_a <gphi *> (use_stmt), index);
> +         if (e->src != def_bb)
> +           add_block = e->src;
> +       }
> +      else if (is_gimple_debug (use_stmt))
> +       continue;
> +      else
> +       {
> +         /* If its not defined in this block, its live on entry.  */
> +         basic_block use_bb = gimple_bb (use_stmt);
> +         if (use_bb != def_bb)
> +           add_block = use_bb;
> +       }
> +
> +      /* If there was a live on entry use, increment register used.  */
> +      if (add_block)
> +       {
> +         regs_used++;
> +       }
> +    }
> +  return regs_used;
> +}
> +
>  /* For each size of the induction variable set determine the penalty.  */
>
>  static void
> @@ -6200,15 +6262,20 @@ determine_set_costs (struct ivopts_data *data)
>        n++;
>      }
>
> +  unsigned max = 0;
>    EXECUTE_IF_SET_IN_BITMAP (data->relevant, 0, j, bi)
>      {
>        struct version_info *info = ver_info (data, j);
> -
>        if (info->inv_id && info->has_nonlin_use)
> -       n++;
> +       {
> +         tree ssa_name = ssa_name (j);
> +         n = get_regs_used (ssa_name);
> +         if (n >= max)
> +           max = n;
> +       }
>      }
>
> -  data->regs_used = n;
> +  data->regs_used = max;
>    if (dump_file && (dump_flags & TDF_DETAILS))
>      fprintf (dump_file, "  regs_used %d\n", n);
>
> --
> 2.39.3
>
>