> It's not necessarily right. unroll_factor will be set as 1 when
> -fno-unroll-loops, which is exactly -fno-unroll-loops means.
Not that exactly, -fno-unroll-loops previously will prevent the pass
from running, and on the current trunk the pass still runs.
Actually I think the implementation on trunk is a bit tricky since we
use a target hook without return value to execute the pass. Also the
logic !OPTION_SET_P looks quite like a workaround. IMHO this is also
not good for maintenance.
Hongtao Liu via Gcc-patches <gcc-patches@gcc.gnu.org> 于2022年11月21日周一 09:33写道：
>
> On Mon, Nov 21, 2022 at 9:01 AM Liu, Hongtao via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Wang, Hongyu <hongyu.w...@intel.com>
> > > Sent: Saturday, November 19, 2022 2:26 PM
> > > To: gcc-patches@gcc.gnu.org
> > > Cc: richard.guent...@gmail.com; ubiz...@gmail.com; Liu, Hongtao
> > > <hongtao....@intel.com>
> > > Subject: [PATCH] i386: Only enable small loop unrolling in backend [PR
> > > 107602]
> > >
> > > Hi,
> > >
> > > Followed by the discussion in pr107602, -munroll-only-small-loops Does not
> > PR107692?
> > > turns on/off -funroll-loops, and current check in
> > > pass_rtl_unroll_loops::gate
> > > would cause -funroll-loops do not take effect. Revert the change about
> It's not necessarily right. unroll_factor will be set as 1 when
> -fno-unroll-loops, which is exactly -fno-unroll-loops means.
> > > targetm.loop_unroll_adjust and apply the backend option change to strictly
> > > follow the rule that -funroll-loops takes full control of loop unrolling,
> > > and
> > > munroll-only-small-loops just change its behavior to unroll small size
> > > loops.
> > >
> > > Bootstrapped and regtested on x86-64-pc-linux-gnu.
> > >
> > > Ok for trunk?
> > >
> > > gcc/ChangeLog:
> > >
> > > PR target/107602
> > > * common/config/i386/i386-common.cc (ix86_optimization_table):
> > > Enable loop unroll O2, disable -fweb and -frename-registers
> > > by default.
> > > * config/i386/i386-options.cc
> > > (ix86_override_options_after_change):
> > > Disable small loop unroll when funroll-loops enabled, reset
> > > cunroll_grow_size when it is not explicitly enabled.
> > > (ix86_option_override_internal): Call
> > > ix86_override_options_after_change instead of calling
> > > ix86_recompute_optlev_based_flags and ix86_default_align
> > > separately.
> > > * config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
> > > factor if -munroll-only-small-loops enabled.
> > > * loop-init.cc (pass_rtl_unroll_loops::gate): Do not enable
> > > loop unrolling for -O2-speed.
> > > (pass_rtl_unroll_loops::execute): Rmove
> > > targetm.loop_unroll_adjust check.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > PR target/107602
> > > * gcc.target/i386/pr86270.c: Add -fno-unroll-loops.
> > > * gcc.target/i386/pr93002.c: Likewise.
> > > ---
> > > gcc/common/config/i386/i386-common.cc | 8 ++++++
> > > gcc/config/i386/i386-options.cc | 34 ++++++++++++++++++++++---
> > > gcc/config/i386/i386.cc | 18 ++++---------
> > > gcc/loop-init.cc | 11 +++-----
> > > gcc/testsuite/gcc.target/i386/pr86270.c | 2 +-
> > > gcc/testsuite/gcc.target/i386/pr93002.c | 2 +-
> > > 6 files changed, 49 insertions(+), 26 deletions(-)
> > >
> > > diff --git a/gcc/common/config/i386/i386-common.cc
> > > b/gcc/common/config/i386/i386-common.cc
> > > index 6ce2a588adc..660a977b68b 100644
> > > --- a/gcc/common/config/i386/i386-common.cc
> > > +++ b/gcc/common/config/i386/i386-common.cc
> > > @@ -1808,7 +1808,15 @@ static const struct default_options
> > > ix86_option_optimization_table[] =
> > > /* The STC algorithm produces the smallest code at -Os, for x86. */
> > > { OPT_LEVELS_2_PLUS, OPT_freorder_blocks_algorithm_, NULL,
> > > REORDER_BLOCKS_ALGORITHM_STC },
> > > +
> > > + /* Turn on -funroll-loops with -munroll-only-small-loops to enable
> > > small
> > > + loop unrolling at -O2. */
> > > + { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_funroll_loops, NULL, 1 },
> > > { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_munroll_only_small_loops, NULL,
> > > 1 },
> > > + /* Turns off -frename-registers and -fweb which are enabled by
> > > + funroll-loops. */
> > > + { OPT_LEVELS_ALL, OPT_frename_registers, NULL, 0 },
> > > + { OPT_LEVELS_ALL, OPT_fweb, NULL, 0 },
> > > /* Turn off -fschedule-insns by default. It tends to make the
> > > problem with not enough registers even worse. */
> > > { OPT_LEVELS_ALL, OPT_fschedule_insns, NULL, 0 }, diff --git
> > > a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc index
> > > e5c77f3a84d..bc1d36e36a8 100644
> > > --- a/gcc/config/i386/i386-options.cc
> > > +++ b/gcc/config/i386/i386-options.cc
> > > @@ -1838,8 +1838,37 @@ ix86_recompute_optlev_based_flags (struct
> > > gcc_options *opts, void ix86_override_options_after_change (void) {
> > > + /* Default align_* from the processor table. */
> > > ix86_default_align (&global_options);
> > > +
> > > ix86_recompute_optlev_based_flags (&global_options,
> > > &global_options_set);
> > > +
> > > + /* Disable unrolling small loops when there's explicit
> > > + -f{,no}unroll-loop. */
> > > + if ((OPTION_SET_P (flag_unroll_loops))
> > > + || (OPTION_SET_P (flag_unroll_all_loops)
> > > + && flag_unroll_all_loops))
> > > + {
> > > + if (!OPTION_SET_P (ix86_unroll_only_small_loops))
> > > + ix86_unroll_only_small_loops = 0;
> > > + /* Re-enable -frename-registers and -fweb if funroll-loops
> > > + enabled. */
> > > + if (!OPTION_SET_P (flag_web))
> > > + flag_web = flag_unroll_loops;
> > > + if (!OPTION_SET_P (flag_rename_registers))
> > > + flag_rename_registers = flag_unroll_loops;
> > > + /* -fcunroll-grow-size default follws -f[no]-unroll-loops. */
> > > + if (!OPTION_SET_P (flag_cunroll_grow_size))
> > > + flag_cunroll_grow_size = flag_unroll_loops
> > > + || flag_peel_loops
> > > + || optimize >= 3;
> > > + }
> > > + else
> > > + {
> > > + if (!OPTION_SET_P (flag_cunroll_grow_size))
> > > + flag_cunroll_grow_size = flag_peel_loops || optimize >= 3;
> > > + }
> > > +
> > > }
> > >
> > > /* Clear stack slot assignments remembered from previous functions.
> > > @@ -2351,7 +2380,7 @@ ix86_option_override_internal (bool main_args_p,
> > >
> > > set_ix86_tune_features (opts, ix86_tune, opts->x_ix86_dump_tunes);
> > >
> > > - ix86_recompute_optlev_based_flags (opts, opts_set);
> > > + ix86_override_options_after_change ();
> > >
> > > ix86_tune_cost = processor_cost_table[ix86_tune];
> > > /* TODO: ix86_cost should be chosen at instruction or function
> > > granuality
> > > @@ -2382,9 +2411,6 @@ ix86_option_override_internal (bool main_args_p,
> > > || TARGET_64BIT_P (opts->x_ix86_isa_flags))
> > > opts->x_ix86_regparm = REGPARM_MAX;
> > >
> > > - /* Default align_* from the processor table. */
> > > - ix86_default_align (opts);
> > > -
> > > /* Provide default for -mbranch-cost= value. */
> > > SET_OPTION_IF_UNSET (opts, opts_set, ix86_branch_cost,
> > > ix86_tune_cost->branch_cost);
> > > diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc index
> > > 292b32c5e99..10f8b4e91a5 100644
> > > --- a/gcc/config/i386/i386.cc
> > > +++ b/gcc/config/i386/i386.cc
> > > @@ -23829,20 +23829,12 @@ ix86_loop_unroll_adjust (unsigned nunroll,
> > > class loop *loop)
> > >
> > > /* Unroll small size loop when unroll factor is not explicitly
> > > specified. */
> > > - if (!(flag_unroll_loops
> > > - || flag_unroll_all_loops
> > > - || loop->unroll))
> > > + if (ix86_unroll_only_small_loops && !loop->unroll)
> > > {
> > > - nunroll = 1;
> > > -
> > > - /* Any explicit -f{no-}unroll-{all-}loops turns off
> > > - -munroll-only-small-loops. */
> > > - if (ix86_unroll_only_small_loops
> > > - && !OPTION_SET_P (flag_unroll_loops)
> > > - && loop->ninsns <= ix86_cost->small_unroll_ninsns)
> > > - nunroll = ix86_cost->small_unroll_factor;
> > > -
> > > - return nunroll;
> > > + if (loop->ninsns <= ix86_cost->small_unroll_ninsns)
> > > + return MIN (nunroll, ix86_cost->small_unroll_factor);
> > > + else
> > > + return 1;
> > > }
> > >
> > > if (!TARGET_ADJUST_UNROLL)
> > > diff --git a/gcc/loop-init.cc b/gcc/loop-init.cc index
> > > 9789efa1e11..f03c077cae1
> > > 100644
> > > --- a/gcc/loop-init.cc
> > > +++ b/gcc/loop-init.cc
> > > @@ -565,12 +565,10 @@ public:
> > > {}
> > >
> > > /* opt_pass methods: */
> > > - bool gate (function *fun) final override
> > > + bool gate (function *) final override
> > > {
> > > - return (flag_unroll_loops || flag_unroll_all_loops ||
> > > cfun->has_unroll
> > > - || (targetm.loop_unroll_adjust
> > > - && optimize >= 2
> > > - && optimize_function_for_speed_p (fun)));
> > > + return (flag_unroll_loops || flag_unroll_all_loops
> > > + || cfun->has_unroll);
> > > }
> > >
> > > unsigned int execute (function *) final override; @@ -586,8 +584,7 @@
> > > pass_rtl_unroll_loops::execute (function *fun)
> > > if (dump_file)
> > > df_dump (dump_file);
> > >
> > > - if (flag_unroll_loops
> > > - || targetm.loop_unroll_adjust)
> > > + if (flag_unroll_loops)
> > > flags |= UAP_UNROLL;
> > > if (flag_unroll_all_loops)
> > > flags |= UAP_UNROLL_ALL;
> > > diff --git a/gcc/testsuite/gcc.target/i386/pr86270.c
> > > b/gcc/testsuite/gcc.target/i386/pr86270.c
> > > index cbc9fbb0450..98b012caf23 100644
> > > --- a/gcc/testsuite/gcc.target/i386/pr86270.c
> > > +++ b/gcc/testsuite/gcc.target/i386/pr86270.c
> > > @@ -1,5 +1,5 @@
> > > /* { dg-do compile } */
> > > -/* { dg-options "-O2 -mno-unroll-only-small-loops" } */
> > > +/* { dg-options "-O2 -fno-unroll-loops" } */
> > >
> > > int *a;
> > > long len;
> > > diff --git a/gcc/testsuite/gcc.target/i386/pr93002.c
> > > b/gcc/testsuite/gcc.target/i386/pr93002.c
> > > index f75a847f75d..7e2d869e17b 100644
> > > --- a/gcc/testsuite/gcc.target/i386/pr93002.c
> > > +++ b/gcc/testsuite/gcc.target/i386/pr93002.c
> > > @@ -1,6 +1,6 @@
> > > /* PR target/93002 */
> > > /* { dg-do compile } */
> > > -/* { dg-options "-O2 -mno-unroll-only-small-loops" } */
> > > +/* { dg-options "-O2 -fno-unroll-loops" } */
> > > /* { dg-final { scan-assembler-not "cmp\[^\n\r]*-1" } } */
> > >
> > > volatile int sink;
> > > --
> > > 2.18.1
> >
>
>
> --
> BR,
> Hongtao
