> Ugh, that's all quite ugly and unmaintainable, no?
Agreed, I have the same feeling.
> I'm quite sure that if this works it's not by intention. Doesn't this
> also disable
> register renaming and web when the user explicitely specifies -funroll-loops?
>
> Doesn't this change -funroll-loops behavior everywhere, only unrolling small
> loops?
The ugly part ensures that -funroll-loops would not be affected at all
by -munroll-only-small-loops.
>
> I'd like to see a -munroll-only-small-loops addition that doesn't have any
> such
> effects. Note RTL unrolling could also
> conditionally enabled on a new -funroll-small-loops which wouldn't enable
> register renaming or web.
Did you mean something like
index b9e07973dd6..b707d4afb84 100644
--- a/gcc/loop-init.cc
+++ b/gcc/loop-init.cc
@@ -567,7 +567,8 @@ public:
/* opt_pass methods: */
bool gate (function *) final override
{
- return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll);
+ return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll
+ || flag_unroll_only_small_loops);
}
then the backend can turn it on by default in O2?
I don't know if there is a way to turn on middle-end pass by
target-specific flags.
Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> 于2022年10月28日周五 15:33写道：
>
> On Wed, Oct 26, 2022 at 7:53 AM Hongyu Wang <hongyu.w...@intel.com> wrote:
> >
> > Hi,
> >
> > Inspired by rs6000 and s390 port changes, this patch
> > enables loop unrolling for small size loop at O2 by default.
> > The default behavior is to unroll loop with unknown trip-count and
> > less than 4 insns by 1 time.
> >
> > This improves 548.exchange2 by 3.5% on icelake and 6% on zen3 with
> > 1.2% codesize increment. For other benchmarks the variants are minor
> > and overall codesize increased by 0.2%.
> >
> > The kernel image size increased by 0.06%, and no impact on eembc.
> >
> > Bootstrapped & regrtested on x86_64-pc-linux-gnu.
> >
> > Ok for trunk?
> >
> > gcc/ChangeLog:
> >
> > * common/config/i386/i386-common.cc (ix86_optimization_table):
> > Enable loop unroll and small loop unroll at O2 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.
> > * config/i386/i386.opt: Add -munroll-only-small-loops,
> > -param=x86-small-unroll-ninsns= for loop insn limit,
> > -param=x86-small-unroll-factor= for unroll factor.
> > * doc/invoke.texi: Document -munroll-only-small-loops,
> > x86-small-unroll-ninsns and x86-small-unroll-factor.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
> > * gcc.target/i386/pr93002.c: Likewise.
> > ---
> > gcc/common/config/i386/i386-common.cc | 6 ++++
> > gcc/config/i386/i386-options.cc | 40 ++++++++++++++++++++++---
> > gcc/config/i386/i386.cc | 13 ++++++++
> > gcc/config/i386/i386.opt | 13 ++++++++
> > gcc/doc/invoke.texi | 14 +++++++++
> > gcc/testsuite/gcc.target/i386/pr86270.c | 2 +-
> > gcc/testsuite/gcc.target/i386/pr93002.c | 2 +-
> > 7 files changed, 84 insertions(+), 6 deletions(-)
> >
> > diff --git a/gcc/common/config/i386/i386-common.cc
> > b/gcc/common/config/i386/i386-common.cc
> > index d6a68dc9b1d..0e580b39d14 100644
> > --- a/gcc/common/config/i386/i386-common.cc
> > +++ b/gcc/common/config/i386/i386-common.cc
> > @@ -1686,6 +1686,12 @@ 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 },
> > + { 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 },
>
> I'm quite sure that if this works it's not by intention. Doesn't this
> also disable
> register renaming and web when the user explicitely specifies -funroll-loops?
>
> Doesn't this change -funroll-loops behavior everywhere, only unrolling small
> loops?
>
> I'd like to see a -munroll-only-small-loops addition that doesn't have any
> such
> effects. Note RTL unrolling could also
> conditionally enabled on a new -funroll-small-loops which wouldn't enable
> register renaming or web.
>
> > /* 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 acb2291e70f..6ea347c32e1 100644
> > --- a/gcc/config/i386/i386-options.cc
> > +++ b/gcc/config/i386/i386-options.cc
> > @@ -1819,8 +1819,43 @@ 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;
> > + 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;
> > + /* Disables loop unrolling if -mno-unroll-only-small-loops is
> > + explicitly set and -funroll-loops is not enabled. */
> > + if (OPTION_SET_P (ix86_unroll_only_small_loops)
> > + && !ix86_unroll_only_small_loops
> > + && !(OPTION_SET_P (flag_unroll_loops)
> > + || OPTION_SET_P (flag_unroll_all_loops)))
> > + flag_unroll_loops = flag_unroll_all_loops = 0;
> > + }
>
> Ugh, that's all quite ugly and unmaintainable, no?
>
> > +
> > }
> >
> > /* Clear stack slot assignments remembered from previous functions.
> > @@ -2332,7 +2367,7 @@ 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
> > @@ -2363,9 +2398,6 @@ 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 480db35f6cd..75829a5d0f4 100644
> > --- a/gcc/config/i386/i386.cc
> > +++ b/gcc/config/i386/i386.cc
> > @@ -23820,6 +23820,19 @@ ix86_loop_unroll_adjust (unsigned nunroll, class
> > loop *loop)
> > unsigned i;
> > unsigned mem_count = 0;
> >
> > + /* Unroll small size loop when unroll factor is not explicitly
> > + specified. */
> > + if (ix86_unroll_only_small_loops && !loop->unroll)
> > + {
> > + int small_unroll = 0;
> > + if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)
> > + small_unroll = MIN ((unsigned) ix86_small_unroll_factor,
> > + nunroll);
> > + else
> > + small_unroll = 1;
> > + return small_unroll;
> > + }
> > +
> > if (!TARGET_ADJUST_UNROLL)
> > return nunroll;
> >
> > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > index 0dbaacb57ed..a724c73c0c4 100644
> > --- a/gcc/config/i386/i386.opt
> > +++ b/gcc/config/i386/i386.opt
> > @@ -1214,3 +1214,16 @@ Do not use GOT to access external symbols.
> > -param=x86-stlf-window-ninsns=
> > Target Joined UInteger Var(x86_stlf_window_ninsns) Init(64) Param
> > Instructions number above which STFL stall penalty can be compensated.
> > +
> > +munroll-only-small-loops
> > +Target Var(ix86_unroll_only_small_loops) Init(0) Save
> > +Enable conservative small loop unrolling.
> > +
> > +-param=x86-small-unroll-ninsns=
> > +Target Joined UInteger Var(ix86_small_unroll_ninsns) Init(4) Param
> > +Insturctions number limit for loop to be unrolled under
> > +-munroll-only-small-loops.
> > +
> > +-param=x86-small-unroll-factor=
> > +Target Joined UInteger Var(ix86_small_unroll_factor) Init(2) Param
> > +Unroll factor for -munroll-only-small-loops.
> > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> > index cd4d3c1d72c..b6fa79eccc3 100644
> > --- a/gcc/doc/invoke.texi
> > +++ b/gcc/doc/invoke.texi
> > @@ -15779,6 +15779,14 @@ The following choices of @var{name} are available
> > on i386 and x86_64 targets:
> > @item x86-stlf-window-ninsns
> > Instructions number above which STFL stall penalty can be compensated.
> >
> > +@item x86-small-unroll-ninsns
> > +If -munroll-only-small-loops is enabled, only unroll loops with instruction
> > +count less than this parameter. The default value is 4.
> > +
> > +@item x86-small-unroll-factor
> > +If -munroll-only-small-loops is enabled, reset the unroll factor with this
> > +value. The default value is 2 which means the loop will be unrolled once.
> > +
> > @end table
> >
> > @end table
> > @@ -25186,6 +25194,12 @@ environments where no dynamic link is performed,
> > like firmwares, OS
> > kernels, executables linked with @option{-static} or @option{-static-pie}.
> > @option{-mdirect-extern-access} is not compatible with @option{-fPIC} or
> > @option{-fpic}.
> > +
> > +@item -munroll-only-small-loops
> > +@itemx -mno-unroll-only-small-loops
> > +@opindex munroll-only-small-loops
> > +Controls conservative small loop unrolling. It is default enbaled by
> > +O2, and unrolls loop with less than 4 insns by 1 time.
> > @end table
> >
> > @node M32C Options
> > diff --git a/gcc/testsuite/gcc.target/i386/pr86270.c
> > b/gcc/testsuite/gcc.target/i386/pr86270.c
> > index 81841ef5bd7..cbc9fbb0450 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" } */
> > +/* { dg-options "-O2 -mno-unroll-only-small-loops" } */
> >
> > int *a;
> > long len;
> > diff --git a/gcc/testsuite/gcc.target/i386/pr93002.c
> > b/gcc/testsuite/gcc.target/i386/pr93002.c
> > index 0248fcc00a5..f75a847f75d 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" } */
> > +/* { dg-options "-O2 -mno-unroll-only-small-loops" } */
> > /* { dg-final { scan-assembler-not "cmp\[^\n\r]*-1" } } */
> >
> > volatile int sink;
> > --
> > 2.18.1
> >
