On Mon, Sep 06, 2021 at 11:18:47AM +0200, Richard Biener wrote:
> On Mon, Sep 6, 2021 at 10:47 AM liuhongt via Gcc-patches
> <[email protected]> wrote:
> >
> > Hi:
> > As discussed in [1], most of (currently unopposed) targets want
> > auto-vectorization at O2, and IMHO now would be a good time to enable O2
> > vectorization for GCC trunk, so it would leave enough time to expose
> > related issues and fix them.
> >
> > Bootstrapped and regtested on x86_64-linux-gnu{-m32,}
> > Ok for trunk?
>
> It changes the cost model used when the user specifices
> -O2 -ftree-vectorize which used 'cheap' before but now sticks to
> 'very-cheap'. I guess adjusting the cost model in process_options
> might be possible when any(?) of the vectorizer flags were set
> explicitly?
process_options would mean it affects only the command line and not
__attribute__((optimize ("O2", "ftree-vectorize")))
etc.
So, shouldn't it be instead done in default_options_optimization, somewhere
among the
if (openacc_mode)
SET_OPTION_IF_UNSET (opts, opts_set, flag_ipa_pta, true);
/* Track fields in field-sensitive alias analysis. */
if (opt2)
SET_OPTION_IF_UNSET (opts, opts_set, param_max_fields_for_field_sensitive,
100);
if (opts->x_optimize_size)
/* We want to crossjump as much as possible. */
SET_OPTION_IF_UNSET (opts, opts_set, param_min_crossjump_insns, 1);
/* Restrict the amount of work combine does at -Og while retaining
most of its useful transforms. */
if (opts->x_optimize_debug)
SET_OPTION_IF_UNSET (opts, opts_set, param_max_combine_insns, 2);
in there?
Like:
/* Use -fvect-cost-model=cheap instead of -fvect-cost-mode=very-cheap
by default with explicit -ftree-{loop,slp}-vectorize. */
if (opts->x_optimize == 2
&& (opts_set->x_ftree_loop_vectorize
|| opts_set->x_ftree_slp_vectorize))
SET_OPTION_IF_UNSET (opts, opts_set, fvect_cost_model_,
VECT_COST_MODEL_CHEAP);
Though, unsure if that will work with -O2 -ftree-vectorize which is an
option without flag with EnabledBy on the other two options.
Also, is:
+ { OPT_LEVELS_2_PLUS, OPT_ftree_loop_vectorize, NULL, 1 },
+ { OPT_LEVELS_2_PLUS, OPT_ftree_slp_vectorize, NULL, 1 },
what we really want, isn't that instead:
+ { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_ftree_loop_vectorize, NULL, 1 },
+ { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_ftree_slp_vectorize, NULL, 1 },
? I mean, for -Os vectorization even in very-cheap model I'd think it
usually enlarges code size, and for -Og it is seriously harmful for
debugging experience, especially when DWARF <= 5 doesn't have anything that
would help debugging vectorized loops.
Jakub
