[PATCH] Add flag to control straight-line strength reduction

[Richard Guenther]

On Tue, 17 Jul 2012, William J. Schmidt wrote:

> I overlooked adding a pass-control flag for strength reduction, added
> here.  I named it -ftree-slsr for consistency with other -ftree- flags,
> but could change it to -fgimple-slsr if you prefer that for a pass named
> gimple-ssa-...
> 
> Bootstrapped and tested on powerpc-unknown-linux-gnu with no new
> regressions.  Ok for trunk?

The switch needs documentation in doc/invoke.texi.  Other than that
it's fine to stick with -ftree-..., even that exposes details to our
users that are not necessary (RTL passes didn't have -frtl-... either).
So in the end, why not re-use -fstrength-reduce that is already available
(but stubbed out)?

Comments from other folks?

Thanks,
Richard.

> Thanks,
> Bill
> 
> 
> 2012-07-17  Bill Schmidt  <wschmidt@linux.ibm.com>
> 
> 	* opts.c (default_option): Make -ftree-slsr default at -O1 and above.
> 	* gimple-ssa-strength-reduction.c (gate_strength_reduction): Use
> 	flag_tree_slsr.
> 	* common.opt: Add -ftree-slsr with flag_tree_slsr.
> 
> 
> Index: gcc/opts.c
> ===================================================================
> --- gcc/opts.c	(revision 189574)
> +++ gcc/opts.c	(working copy)
> @@ -452,6 +452,7 @@ static const struct default_options default_option
>      { OPT_LEVELS_1_PLUS, OPT_ftree_ch, NULL, 1 },
>      { OPT_LEVELS_1_PLUS, OPT_fcombine_stack_adjustments, NULL, 1 },
>      { OPT_LEVELS_1_PLUS, OPT_fcompare_elim, NULL, 1 },
> +    { OPT_LEVELS_1_PLUS, OPT_ftree_slsr, NULL, 1 },
>  
>      /* -O2 optimizations.  */
>      { OPT_LEVELS_2_PLUS, OPT_finline_small_functions, NULL, 1 },
> Index: gcc/gimple-ssa-strength-reduction.c
> ===================================================================
> --- gcc/gimple-ssa-strength-reduction.c	(revision 189574)
> +++ gcc/gimple-ssa-strength-reduction.c	(working copy)
> @@ -1501,7 +1501,7 @@ execute_strength_reduction (void)
>  static bool
>  gate_strength_reduction (void)
>  {
> -  return optimize > 0;
> +  return flag_tree_slsr;
>  }
>  
>  struct gimple_opt_pass pass_strength_reduction =
> Index: gcc/common.opt
> ===================================================================
> --- gcc/common.opt	(revision 189574)
> +++ gcc/common.opt	(working copy)
> @@ -2080,6 +2080,10 @@ ftree-sink
>  Common Report Var(flag_tree_sink) Optimization
>  Enable SSA code sinking on trees
>  
> +ftree-slsr
> +Common Report Var(flag_tree_slsr) Optimization
> +Perform straight-line strength reduction
> +
>  ftree-sra
>  Common Report Var(flag_tree_sra) Optimization
>  Perform scalar replacement of aggregates
> 
> 
> 

-- 
Richard Guenther <rguenther@suse.de>
SUSE / SUSE Labs
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