[V2] Enable small loop unrolling for O2

  Hi, this is the updated patch of
https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604345.html,
which uses targetm.loop_unroll_adjust as gate to enable small loop unroll.

This patch does not change rs6000/s390 since I don't have machine to 
test them, but I suppose the default behavior is the same since they
enable flag_unroll_loops at O2.

Bootstrapped & regrtested on x86_64-pc-linux-gnu.

Ok for trunk?

---------- Patch content --------

Modern processors has multiple way instruction decoders
For x86, icelake/zen3 has 5 uops, so for small loop with <= 4
instructions (usually has 3 uops with a cmp/jmp pair that can be
macro-fused), the decoder would have 2 uops bubble for each iteration
and the pipeline could not be fully utilized.

Therefore, this patch enables loop unrolling for small size loop at O2
to fullfill the decoder as much as possible. It turns on rtl loop
unrolling when targetm.loop_unroll_adjust exists and O2 plus speed only.
In x86 backend the default behavior is to unroll small loops with less
than 4 insns by 1 time.

This improves 548.exchange2 by 9% on icelake and 7.4% on zen3 with
0.9% 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.

gcc/ChangeLog:

	* common/config/i386/i386-common.cc (ix86_optimization_table):
	Enable small loop unroll at O2 by default.
	* config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
	factor if -munroll-only-small-loops enabled and -funroll-loops/
	-funroll-all-loops are disabled.
	* 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.
	* loop-init.cc (pass_rtl_unroll_loops::gate): Enable rtl
	loop unrolling for -O2-speed and above if target hook
	loop_unroll_adjust exists.

gcc/testsuite/ChangeLog:

	* gcc.dg/guality/loop-1.c: Add additional option
	  -mno-unroll-only-small-loops.
	* gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
	* gcc.target/i386/pr93002.c: Likewise.
---
 gcc/common/config/i386/i386-common.cc   |  1 +
 gcc/config/i386/i386.cc                 | 18 ++++++++++++++++++
 gcc/config/i386/i386.opt                | 13 +++++++++++++
 gcc/doc/invoke.texi                     | 16 ++++++++++++++++
 gcc/loop-init.cc                        | 10 +++++++---
 gcc/testsuite/gcc.dg/guality/loop-1.c   |  2 ++
 gcc/testsuite/gcc.target/i386/pr86270.c |  2 +-
 gcc/testsuite/gcc.target/i386/pr93002.c |  2 +-
 8 files changed, 59 insertions(+), 5 deletions(-)
  

On Wed, Nov 2, 2022 at 4:37 AM Hongyu Wang <hongyu.wang@intel.com> wrote:
>
> Hi, this is the updated patch of
> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604345.html,
> which uses targetm.loop_unroll_adjust as gate to enable small loop unroll.
>
> This patch does not change rs6000/s390 since I don't have machine to
> test them, but I suppose the default behavior is the same since they
> enable flag_unroll_loops at O2.
>
> Bootstrapped & regrtested on x86_64-pc-linux-gnu.
>
> Ok for trunk?
>
> ---------- Patch content --------
>
> Modern processors has multiple way instruction decoders
> For x86, icelake/zen3 has 5 uops, so for small loop with <= 4
> instructions (usually has 3 uops with a cmp/jmp pair that can be
> macro-fused), the decoder would have 2 uops bubble for each iteration
> and the pipeline could not be fully utilized.
>
> Therefore, this patch enables loop unrolling for small size loop at O2
> to fullfill the decoder as much as possible. It turns on rtl loop
> unrolling when targetm.loop_unroll_adjust exists and O2 plus speed only.
> In x86 backend the default behavior is to unroll small loops with less
> than 4 insns by 1 time.
>
> This improves 548.exchange2 by 9% on icelake and 7.4% on zen3 with
> 0.9% 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.
>
> gcc/ChangeLog:
>
>         * common/config/i386/i386-common.cc (ix86_optimization_table):
>         Enable small loop unroll at O2 by default.
>         * config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
>         factor if -munroll-only-small-loops enabled and -funroll-loops/
>         -funroll-all-loops are disabled.
>         * 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.
>         * loop-init.cc (pass_rtl_unroll_loops::gate): Enable rtl
>         loop unrolling for -O2-speed and above if target hook
>         loop_unroll_adjust exists.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/guality/loop-1.c: Add additional option
>           -mno-unroll-only-small-loops.
>         * gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
>         * gcc.target/i386/pr93002.c: Likewise.
> ---
>  gcc/common/config/i386/i386-common.cc   |  1 +
>  gcc/config/i386/i386.cc                 | 18 ++++++++++++++++++
>  gcc/config/i386/i386.opt                | 13 +++++++++++++
>  gcc/doc/invoke.texi                     | 16 ++++++++++++++++
>  gcc/loop-init.cc                        | 10 +++++++---
>  gcc/testsuite/gcc.dg/guality/loop-1.c   |  2 ++
>  gcc/testsuite/gcc.target/i386/pr86270.c |  2 +-
>  gcc/testsuite/gcc.target/i386/pr93002.c |  2 +-
>  8 files changed, 59 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/common/config/i386/i386-common.cc b/gcc/common/config/i386/i386-common.cc
> index f66bdd5a2af..c6891486078 100644
> --- a/gcc/common/config/i386/i386-common.cc
> +++ b/gcc/common/config/i386/i386-common.cc
> @@ -1724,6 +1724,7 @@ 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_munroll_only_small_loops, NULL, 1 },
>      /* 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.cc b/gcc/config/i386/i386.cc
> index c0f37149ed0..0f94a3b609e 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -23827,6 +23827,24 @@ 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 (!(flag_unroll_loops
> +       || flag_unroll_all_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))
> +       if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)

either add braces or combine the two if's

Otherwise the middle-end changes look OK.  The target maintainers need to decide
whether the two --params should be core tunings instead - I would assume that
given your rationale the decode and issue widths of the core plays an important
role here.  That might also suggest a single parameter instead and unrolling
(factor * issue_width) / loop->ninsns times instead of a static unroll_factor?

Thanks,
Richard.

> +         nunroll = (unsigned) ix86_small_unroll_factor;
> +
> +      return nunroll;
> +    }
> +
>    if (!TARGET_ADJUST_UNROLL)
>       return nunroll;
>
> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> index 53d534f6392..6da9c8d670d 100644
> --- a/gcc/config/i386/i386.opt
> +++ b/gcc/config/i386/i386.opt
> @@ -1224,3 +1224,16 @@ mavxvnniint8
>  Target Mask(ISA2_AVXVNNIINT8) Var(ix86_isa_flags2) Save
>  Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2 and
>  AVXVNNIINT8 built-in functions and code generation.
> +
> +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 550aec87809..487218bd0ce 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -15821,6 +15821,14 @@ 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
> @@ -25232,6 +25240,14 @@ 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. Explicit
> +-f[no-]unroll-[all-]loops would disable this flag to avoid any
> +unintended unrolling behavior that user does not want.
>  @end table
>
>  @node M32C Options
> diff --git a/gcc/loop-init.cc b/gcc/loop-init.cc
> index b9e07973dd6..9789efa1e11 100644
> --- a/gcc/loop-init.cc
> +++ b/gcc/loop-init.cc
> @@ -565,9 +565,12 @@ public:
>    {}
>
>    /* opt_pass methods: */
> -  bool gate (function *) final override
> +  bool gate (function *fun) final override
>      {
> -      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll);
> +      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll
> +             || (targetm.loop_unroll_adjust
> +                 && optimize >= 2
> +                 && optimize_function_for_speed_p (fun)));
>      }
>
>    unsigned int execute (function *) final override;
> @@ -583,7 +586,8 @@ pass_rtl_unroll_loops::execute (function *fun)
>        if (dump_file)
>         df_dump (dump_file);
>
> -      if (flag_unroll_loops)
> +      if (flag_unroll_loops
> +         || targetm.loop_unroll_adjust)
>         flags |= UAP_UNROLL;
>        if (flag_unroll_all_loops)
>         flags |= UAP_UNROLL_ALL;
> diff --git a/gcc/testsuite/gcc.dg/guality/loop-1.c b/gcc/testsuite/gcc.dg/guality/loop-1.c
> index 1b1f6d32271..a32ea445a3f 100644
> --- a/gcc/testsuite/gcc.dg/guality/loop-1.c
> +++ b/gcc/testsuite/gcc.dg/guality/loop-1.c
> @@ -1,5 +1,7 @@
>  /* { dg-do run } */
>  /* { dg-options "-fno-tree-scev-cprop -fno-tree-vectorize -g" } */
> +/* { dg-additional-options "-mno-unroll-only-small-loops" { target ia32 } } */
> +
>
>  #include "../nop.h"
>
> 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
>
  

On Mon, Nov 7, 2022 at 10:25 PM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Wed, Nov 2, 2022 at 4:37 AM Hongyu Wang <hongyu.wang@intel.com> wrote:
> >
> > Hi, this is the updated patch of
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604345.html,
> > which uses targetm.loop_unroll_adjust as gate to enable small loop unroll.
> >
> > This patch does not change rs6000/s390 since I don't have machine to
> > test them, but I suppose the default behavior is the same since they
> > enable flag_unroll_loops at O2.
> >
> > Bootstrapped & regrtested on x86_64-pc-linux-gnu.
> >
> > Ok for trunk?
> >
> > ---------- Patch content --------
> >
> > Modern processors has multiple way instruction decoders
> > For x86, icelake/zen3 has 5 uops, so for small loop with <= 4
> > instructions (usually has 3 uops with a cmp/jmp pair that can be
> > macro-fused), the decoder would have 2 uops bubble for each iteration
> > and the pipeline could not be fully utilized.
> >
> > Therefore, this patch enables loop unrolling for small size loop at O2
> > to fullfill the decoder as much as possible. It turns on rtl loop
> > unrolling when targetm.loop_unroll_adjust exists and O2 plus speed only.
> > In x86 backend the default behavior is to unroll small loops with less
> > than 4 insns by 1 time.
> >
> > This improves 548.exchange2 by 9% on icelake and 7.4% on zen3 with
> > 0.9% 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.
> >
> > gcc/ChangeLog:
> >
> >         * common/config/i386/i386-common.cc (ix86_optimization_table):
> >         Enable small loop unroll at O2 by default.
> >         * config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
> >         factor if -munroll-only-small-loops enabled and -funroll-loops/
> >         -funroll-all-loops are disabled.
> >         * 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.
> >         * loop-init.cc (pass_rtl_unroll_loops::gate): Enable rtl
> >         loop unrolling for -O2-speed and above if target hook
> >         loop_unroll_adjust exists.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.dg/guality/loop-1.c: Add additional option
> >           -mno-unroll-only-small-loops.
> >         * gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
> >         * gcc.target/i386/pr93002.c: Likewise.
> > ---
> >  gcc/common/config/i386/i386-common.cc   |  1 +
> >  gcc/config/i386/i386.cc                 | 18 ++++++++++++++++++
> >  gcc/config/i386/i386.opt                | 13 +++++++++++++
> >  gcc/doc/invoke.texi                     | 16 ++++++++++++++++
> >  gcc/loop-init.cc                        | 10 +++++++---
> >  gcc/testsuite/gcc.dg/guality/loop-1.c   |  2 ++
> >  gcc/testsuite/gcc.target/i386/pr86270.c |  2 +-
> >  gcc/testsuite/gcc.target/i386/pr93002.c |  2 +-
> >  8 files changed, 59 insertions(+), 5 deletions(-)
> >
> > diff --git a/gcc/common/config/i386/i386-common.cc b/gcc/common/config/i386/i386-common.cc
> > index f66bdd5a2af..c6891486078 100644
> > --- a/gcc/common/config/i386/i386-common.cc
> > +++ b/gcc/common/config/i386/i386-common.cc
> > @@ -1724,6 +1724,7 @@ 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_munroll_only_small_loops, NULL, 1 },
> >      /* 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.cc b/gcc/config/i386/i386.cc
> > index c0f37149ed0..0f94a3b609e 100644
> > --- a/gcc/config/i386/i386.cc
> > +++ b/gcc/config/i386/i386.cc
> > @@ -23827,6 +23827,24 @@ 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 (!(flag_unroll_loops
> > +       || flag_unroll_all_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))
> > +       if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)
>
> either add braces or combine the two if's
>
> Otherwise the middle-end changes look OK.  The target maintainers need to decide
> whether the two --params should be core tunings instead - I would assume that
> given your rationale the decode and issue widths of the core plays an important
> role here.  That might also suggest a single parameter instead and unrolling
> (factor * issue_width) / loop->ninsns times instead of a static unroll_factor?
Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
for codesize.
Make it exact as issue_rate and using factor * issue_width /
loop->ninsns may increase code size too much.
So I prefer to add those 2 parameters to the cost table for core
tunings instead of 1.
>
> Thanks,
> Richard.
>
> > +         nunroll = (unsigned) ix86_small_unroll_factor;
> > +
> > +      return nunroll;
> > +    }
> > +
> >    if (!TARGET_ADJUST_UNROLL)
> >       return nunroll;
> >
> > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > index 53d534f6392..6da9c8d670d 100644
> > --- a/gcc/config/i386/i386.opt
> > +++ b/gcc/config/i386/i386.opt
> > @@ -1224,3 +1224,16 @@ mavxvnniint8
> >  Target Mask(ISA2_AVXVNNIINT8) Var(ix86_isa_flags2) Save
> >  Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2 and
> >  AVXVNNIINT8 built-in functions and code generation.
> > +
> > +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 550aec87809..487218bd0ce 100644
> > --- a/gcc/doc/invoke.texi
> > +++ b/gcc/doc/invoke.texi
> > @@ -15821,6 +15821,14 @@ 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
> > @@ -25232,6 +25240,14 @@ 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. Explicit
> > +-f[no-]unroll-[all-]loops would disable this flag to avoid any
> > +unintended unrolling behavior that user does not want.
> >  @end table
> >
> >  @node M32C Options
> > diff --git a/gcc/loop-init.cc b/gcc/loop-init.cc
> > index b9e07973dd6..9789efa1e11 100644
> > --- a/gcc/loop-init.cc
> > +++ b/gcc/loop-init.cc
> > @@ -565,9 +565,12 @@ public:
> >    {}
> >
> >    /* opt_pass methods: */
> > -  bool gate (function *) final override
> > +  bool gate (function *fun) final override
> >      {
> > -      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll);
> > +      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll
> > +             || (targetm.loop_unroll_adjust
> > +                 && optimize >= 2
> > +                 && optimize_function_for_speed_p (fun)));
> >      }
> >
> >    unsigned int execute (function *) final override;
> > @@ -583,7 +586,8 @@ pass_rtl_unroll_loops::execute (function *fun)
> >        if (dump_file)
> >         df_dump (dump_file);
> >
> > -      if (flag_unroll_loops)
> > +      if (flag_unroll_loops
> > +         || targetm.loop_unroll_adjust)
> >         flags |= UAP_UNROLL;
> >        if (flag_unroll_all_loops)
> >         flags |= UAP_UNROLL_ALL;
> > diff --git a/gcc/testsuite/gcc.dg/guality/loop-1.c b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > index 1b1f6d32271..a32ea445a3f 100644
> > --- a/gcc/testsuite/gcc.dg/guality/loop-1.c
> > +++ b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > @@ -1,5 +1,7 @@
> >  /* { dg-do run } */
> >  /* { dg-options "-fno-tree-scev-cprop -fno-tree-vectorize -g" } */
> > +/* { dg-additional-options "-mno-unroll-only-small-loops" { target ia32 } } */
> > +
> >
> >  #include "../nop.h"
> >
> > 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
> >
  

> Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
> for codesize.
> Make it exact as issue_rate and using factor * issue_width /
> loop->ninsns may increase code size too much.
> So I prefer to add those 2 parameters to the cost table for core
> tunings instead of 1.

Yes, here is the updated patch that changes the cost table.

Bootstrapped & regrtested on x86_64-pc-linux-gnu.

Ok for trunk?

Hongtao Liu via Gcc-patches <gcc-patches@gcc.gnu.org> 于2022年11月8日周二 11:05写道：
>
> On Mon, Nov 7, 2022 at 10:25 PM Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Wed, Nov 2, 2022 at 4:37 AM Hongyu Wang <hongyu.wang@intel.com> wrote:
> > >
> > > Hi, this is the updated patch of
> > > https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604345.html,
> > > which uses targetm.loop_unroll_adjust as gate to enable small loop unroll.
> > >
> > > This patch does not change rs6000/s390 since I don't have machine to
> > > test them, but I suppose the default behavior is the same since they
> > > enable flag_unroll_loops at O2.
> > >
> > > Bootstrapped & regrtested on x86_64-pc-linux-gnu.
> > >
> > > Ok for trunk?
> > >
> > > ---------- Patch content --------
> > >
> > > Modern processors has multiple way instruction decoders
> > > For x86, icelake/zen3 has 5 uops, so for small loop with <= 4
> > > instructions (usually has 3 uops with a cmp/jmp pair that can be
> > > macro-fused), the decoder would have 2 uops bubble for each iteration
> > > and the pipeline could not be fully utilized.
> > >
> > > Therefore, this patch enables loop unrolling for small size loop at O2
> > > to fullfill the decoder as much as possible. It turns on rtl loop
> > > unrolling when targetm.loop_unroll_adjust exists and O2 plus speed only.
> > > In x86 backend the default behavior is to unroll small loops with less
> > > than 4 insns by 1 time.
> > >
> > > This improves 548.exchange2 by 9% on icelake and 7.4% on zen3 with
> > > 0.9% 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.
> > >
> > > gcc/ChangeLog:
> > >
> > >         * common/config/i386/i386-common.cc (ix86_optimization_table):
> > >         Enable small loop unroll at O2 by default.
> > >         * config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
> > >         factor if -munroll-only-small-loops enabled and -funroll-loops/
> > >         -funroll-all-loops are disabled.
> > >         * 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.
> > >         * loop-init.cc (pass_rtl_unroll_loops::gate): Enable rtl
> > >         loop unrolling for -O2-speed and above if target hook
> > >         loop_unroll_adjust exists.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > >         * gcc.dg/guality/loop-1.c: Add additional option
> > >           -mno-unroll-only-small-loops.
> > >         * gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
> > >         * gcc.target/i386/pr93002.c: Likewise.
> > > ---
> > >  gcc/common/config/i386/i386-common.cc   |  1 +
> > >  gcc/config/i386/i386.cc                 | 18 ++++++++++++++++++
> > >  gcc/config/i386/i386.opt                | 13 +++++++++++++
> > >  gcc/doc/invoke.texi                     | 16 ++++++++++++++++
> > >  gcc/loop-init.cc                        | 10 +++++++---
> > >  gcc/testsuite/gcc.dg/guality/loop-1.c   |  2 ++
> > >  gcc/testsuite/gcc.target/i386/pr86270.c |  2 +-
> > >  gcc/testsuite/gcc.target/i386/pr93002.c |  2 +-
> > >  8 files changed, 59 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/gcc/common/config/i386/i386-common.cc b/gcc/common/config/i386/i386-common.cc
> > > index f66bdd5a2af..c6891486078 100644
> > > --- a/gcc/common/config/i386/i386-common.cc
> > > +++ b/gcc/common/config/i386/i386-common.cc
> > > @@ -1724,6 +1724,7 @@ 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_munroll_only_small_loops, NULL, 1 },
> > >      /* 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.cc b/gcc/config/i386/i386.cc
> > > index c0f37149ed0..0f94a3b609e 100644
> > > --- a/gcc/config/i386/i386.cc
> > > +++ b/gcc/config/i386/i386.cc
> > > @@ -23827,6 +23827,24 @@ 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 (!(flag_unroll_loops
> > > +       || flag_unroll_all_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))
> > > +       if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)
> >
> > either add braces or combine the two if's
> >
> > Otherwise the middle-end changes look OK.  The target maintainers need to decide
> > whether the two --params should be core tunings instead - I would assume that
> > given your rationale the decode and issue widths of the core plays an important
> > role here.  That might also suggest a single parameter instead and unrolling
> > (factor * issue_width) / loop->ninsns times instead of a static unroll_factor?
> Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
> for codesize.
> Make it exact as issue_rate and using factor * issue_width /
> loop->ninsns may increase code size too much.
> So I prefer to add those 2 parameters to the cost table for core
> tunings instead of 1.
> >
> > Thanks,
> > Richard.
> >
> > > +         nunroll = (unsigned) ix86_small_unroll_factor;
> > > +
> > > +      return nunroll;
> > > +    }
> > > +
> > >    if (!TARGET_ADJUST_UNROLL)
> > >       return nunroll;
> > >
> > > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > > index 53d534f6392..6da9c8d670d 100644
> > > --- a/gcc/config/i386/i386.opt
> > > +++ b/gcc/config/i386/i386.opt
> > > @@ -1224,3 +1224,16 @@ mavxvnniint8
> > >  Target Mask(ISA2_AVXVNNIINT8) Var(ix86_isa_flags2) Save
> > >  Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2 and
> > >  AVXVNNIINT8 built-in functions and code generation.
> > > +
> > > +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 550aec87809..487218bd0ce 100644
> > > --- a/gcc/doc/invoke.texi
> > > +++ b/gcc/doc/invoke.texi
> > > @@ -15821,6 +15821,14 @@ 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
> > > @@ -25232,6 +25240,14 @@ 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. Explicit
> > > +-f[no-]unroll-[all-]loops would disable this flag to avoid any
> > > +unintended unrolling behavior that user does not want.
> > >  @end table
> > >
> > >  @node M32C Options
> > > diff --git a/gcc/loop-init.cc b/gcc/loop-init.cc
> > > index b9e07973dd6..9789efa1e11 100644
> > > --- a/gcc/loop-init.cc
> > > +++ b/gcc/loop-init.cc
> > > @@ -565,9 +565,12 @@ public:
> > >    {}
> > >
> > >    /* opt_pass methods: */
> > > -  bool gate (function *) final override
> > > +  bool gate (function *fun) final override
> > >      {
> > > -      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll);
> > > +      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll
> > > +             || (targetm.loop_unroll_adjust
> > > +                 && optimize >= 2
> > > +                 && optimize_function_for_speed_p (fun)));
> > >      }
> > >
> > >    unsigned int execute (function *) final override;
> > > @@ -583,7 +586,8 @@ pass_rtl_unroll_loops::execute (function *fun)
> > >        if (dump_file)
> > >         df_dump (dump_file);
> > >
> > > -      if (flag_unroll_loops)
> > > +      if (flag_unroll_loops
> > > +         || targetm.loop_unroll_adjust)
> > >         flags |= UAP_UNROLL;
> > >        if (flag_unroll_all_loops)
> > >         flags |= UAP_UNROLL_ALL;
> > > diff --git a/gcc/testsuite/gcc.dg/guality/loop-1.c b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > index 1b1f6d32271..a32ea445a3f 100644
> > > --- a/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > +++ b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > @@ -1,5 +1,7 @@
> > >  /* { dg-do run } */
> > >  /* { dg-options "-fno-tree-scev-cprop -fno-tree-vectorize -g" } */
> > > +/* { dg-additional-options "-mno-unroll-only-small-loops" { target ia32 } } */
> > > +
> > >
> > >  #include "../nop.h"
> > >
> > > 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
> > >
>
>
>
> --
> BR,
> Hongtao
  

On Wed, Nov 9, 2022 at 9:29 AM Hongyu Wang <wwwhhhyyy333@gmail.com> wrote:
>
> > Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
> > for codesize.
> > Make it exact as issue_rate and using factor * issue_width /
> > loop->ninsns may increase code size too much.
> > So I prefer to add those 2 parameters to the cost table for core
> > tunings instead of 1.
>
> Yes, here is the updated patch that changes the cost table.
>
> Bootstrapped & regrtested on x86_64-pc-linux-gnu.
>
> Ok for trunk?
Ok, Note GCC documents have been ported to sphinx, so you need to
adjust changes in invoke.texi to new sphinx files.
>
> Hongtao Liu via Gcc-patches <gcc-patches@gcc.gnu.org> 于2022年11月8日周二 11:05写道：
> >
> > On Mon, Nov 7, 2022 at 10:25 PM Richard Biener via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > On Wed, Nov 2, 2022 at 4:37 AM Hongyu Wang <hongyu.wang@intel.com> wrote:
> > > >
> > > > Hi, this is the updated patch of
> > > > https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604345.html,
> > > > which uses targetm.loop_unroll_adjust as gate to enable small loop unroll.
> > > >
> > > > This patch does not change rs6000/s390 since I don't have machine to
> > > > test them, but I suppose the default behavior is the same since they
> > > > enable flag_unroll_loops at O2.
> > > >
> > > > Bootstrapped & regrtested on x86_64-pc-linux-gnu.
> > > >
> > > > Ok for trunk?
> > > >
> > > > ---------- Patch content --------
> > > >
> > > > Modern processors has multiple way instruction decoders
> > > > For x86, icelake/zen3 has 5 uops, so for small loop with <= 4
> > > > instructions (usually has 3 uops with a cmp/jmp pair that can be
> > > > macro-fused), the decoder would have 2 uops bubble for each iteration
> > > > and the pipeline could not be fully utilized.
> > > >
> > > > Therefore, this patch enables loop unrolling for small size loop at O2
> > > > to fullfill the decoder as much as possible. It turns on rtl loop
> > > > unrolling when targetm.loop_unroll_adjust exists and O2 plus speed only.
> > > > In x86 backend the default behavior is to unroll small loops with less
> > > > than 4 insns by 1 time.
> > > >
> > > > This improves 548.exchange2 by 9% on icelake and 7.4% on zen3 with
> > > > 0.9% 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.
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > >         * common/config/i386/i386-common.cc (ix86_optimization_table):
> > > >         Enable small loop unroll at O2 by default.
> > > >         * config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
> > > >         factor if -munroll-only-small-loops enabled and -funroll-loops/
> > > >         -funroll-all-loops are disabled.
> > > >         * 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.
> > > >         * loop-init.cc (pass_rtl_unroll_loops::gate): Enable rtl
> > > >         loop unrolling for -O2-speed and above if target hook
> > > >         loop_unroll_adjust exists.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > >         * gcc.dg/guality/loop-1.c: Add additional option
> > > >           -mno-unroll-only-small-loops.
> > > >         * gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
> > > >         * gcc.target/i386/pr93002.c: Likewise.
> > > > ---
> > > >  gcc/common/config/i386/i386-common.cc   |  1 +
> > > >  gcc/config/i386/i386.cc                 | 18 ++++++++++++++++++
> > > >  gcc/config/i386/i386.opt                | 13 +++++++++++++
> > > >  gcc/doc/invoke.texi                     | 16 ++++++++++++++++
> > > >  gcc/loop-init.cc                        | 10 +++++++---
> > > >  gcc/testsuite/gcc.dg/guality/loop-1.c   |  2 ++
> > > >  gcc/testsuite/gcc.target/i386/pr86270.c |  2 +-
> > > >  gcc/testsuite/gcc.target/i386/pr93002.c |  2 +-
> > > >  8 files changed, 59 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/gcc/common/config/i386/i386-common.cc b/gcc/common/config/i386/i386-common.cc
> > > > index f66bdd5a2af..c6891486078 100644
> > > > --- a/gcc/common/config/i386/i386-common.cc
> > > > +++ b/gcc/common/config/i386/i386-common.cc
> > > > @@ -1724,6 +1724,7 @@ 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_munroll_only_small_loops, NULL, 1 },
> > > >      /* 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.cc b/gcc/config/i386/i386.cc
> > > > index c0f37149ed0..0f94a3b609e 100644
> > > > --- a/gcc/config/i386/i386.cc
> > > > +++ b/gcc/config/i386/i386.cc
> > > > @@ -23827,6 +23827,24 @@ 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 (!(flag_unroll_loops
> > > > +       || flag_unroll_all_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))
> > > > +       if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)
> > >
> > > either add braces or combine the two if's
> > >
> > > Otherwise the middle-end changes look OK.  The target maintainers need to decide
> > > whether the two --params should be core tunings instead - I would assume that
> > > given your rationale the decode and issue widths of the core plays an important
> > > role here.  That might also suggest a single parameter instead and unrolling
> > > (factor * issue_width) / loop->ninsns times instead of a static unroll_factor?
> > Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
> > for codesize.
> > Make it exact as issue_rate and using factor * issue_width /
> > loop->ninsns may increase code size too much.
> > So I prefer to add those 2 parameters to the cost table for core
> > tunings instead of 1.
> > >
> > > Thanks,
> > > Richard.
> > >
> > > > +         nunroll = (unsigned) ix86_small_unroll_factor;
> > > > +
> > > > +      return nunroll;
> > > > +    }
> > > > +
> > > >    if (!TARGET_ADJUST_UNROLL)
> > > >       return nunroll;
> > > >
> > > > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > > > index 53d534f6392..6da9c8d670d 100644
> > > > --- a/gcc/config/i386/i386.opt
> > > > +++ b/gcc/config/i386/i386.opt
> > > > @@ -1224,3 +1224,16 @@ mavxvnniint8
> > > >  Target Mask(ISA2_AVXVNNIINT8) Var(ix86_isa_flags2) Save
> > > >  Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2 and
> > > >  AVXVNNIINT8 built-in functions and code generation.
> > > > +
> > > > +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 550aec87809..487218bd0ce 100644
> > > > --- a/gcc/doc/invoke.texi
> > > > +++ b/gcc/doc/invoke.texi
> > > > @@ -15821,6 +15821,14 @@ 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
> > > > @@ -25232,6 +25240,14 @@ 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. Explicit
> > > > +-f[no-]unroll-[all-]loops would disable this flag to avoid any
> > > > +unintended unrolling behavior that user does not want.
> > > >  @end table
> > > >
> > > >  @node M32C Options
> > > > diff --git a/gcc/loop-init.cc b/gcc/loop-init.cc
> > > > index b9e07973dd6..9789efa1e11 100644
> > > > --- a/gcc/loop-init.cc
> > > > +++ b/gcc/loop-init.cc
> > > > @@ -565,9 +565,12 @@ public:
> > > >    {}
> > > >
> > > >    /* opt_pass methods: */
> > > > -  bool gate (function *) final override
> > > > +  bool gate (function *fun) final override
> > > >      {
> > > > -      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll);
> > > > +      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll
> > > > +             || (targetm.loop_unroll_adjust
> > > > +                 && optimize >= 2
> > > > +                 && optimize_function_for_speed_p (fun)));
> > > >      }
> > > >
> > > >    unsigned int execute (function *) final override;
> > > > @@ -583,7 +586,8 @@ pass_rtl_unroll_loops::execute (function *fun)
> > > >        if (dump_file)
> > > >         df_dump (dump_file);
> > > >
> > > > -      if (flag_unroll_loops)
> > > > +      if (flag_unroll_loops
> > > > +         || targetm.loop_unroll_adjust)
> > > >         flags |= UAP_UNROLL;
> > > >        if (flag_unroll_all_loops)
> > > >         flags |= UAP_UNROLL_ALL;
> > > > diff --git a/gcc/testsuite/gcc.dg/guality/loop-1.c b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > > index 1b1f6d32271..a32ea445a3f 100644
> > > > --- a/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > > +++ b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > > @@ -1,5 +1,7 @@
> > > >  /* { dg-do run } */
> > > >  /* { dg-options "-fno-tree-scev-cprop -fno-tree-vectorize -g" } */
> > > > +/* { dg-additional-options "-mno-unroll-only-small-loops" { target ia32 } } */
> > > > +
> > > >
> > > >  #include "../nop.h"
> > > >
> > > > 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
> > > >
> >
> >
> >
> > --
> > BR,
> > Hongtao
  

> Ok, Note GCC documents have been ported to sphinx, so you need to
> adjust changes in invoke.texi to new sphinx files.

Yes, this is the patch I'm going to check-in. Thanks.

Hongtao Liu <crazylht@gmail.com> 于2022年11月14日周一 09:35写道：
>
> On Wed, Nov 9, 2022 at 9:29 AM Hongyu Wang <wwwhhhyyy333@gmail.com> wrote:
> >
> > > Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
> > > for codesize.
> > > Make it exact as issue_rate and using factor * issue_width /
> > > loop->ninsns may increase code size too much.
> > > So I prefer to add those 2 parameters to the cost table for core
> > > tunings instead of 1.
> >
> > Yes, here is the updated patch that changes the cost table.
> >
> > Bootstrapped & regrtested on x86_64-pc-linux-gnu.
> >
> > Ok for trunk?
> Ok, Note GCC documents have been ported to sphinx, so you need to
> adjust changes in invoke.texi to new sphinx files.
> >
> > Hongtao Liu via Gcc-patches <gcc-patches@gcc.gnu.org> 于2022年11月8日周二 11:05写道：
> > >
> > > On Mon, Nov 7, 2022 at 10:25 PM Richard Biener via Gcc-patches
> > > <gcc-patches@gcc.gnu.org> wrote:
> > > >
> > > > On Wed, Nov 2, 2022 at 4:37 AM Hongyu Wang <hongyu.wang@intel.com> wrote:
> > > > >
> > > > > Hi, this is the updated patch of
> > > > > https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604345.html,
> > > > > which uses targetm.loop_unroll_adjust as gate to enable small loop unroll.
> > > > >
> > > > > This patch does not change rs6000/s390 since I don't have machine to
> > > > > test them, but I suppose the default behavior is the same since they
> > > > > enable flag_unroll_loops at O2.
> > > > >
> > > > > Bootstrapped & regrtested on x86_64-pc-linux-gnu.
> > > > >
> > > > > Ok for trunk?
> > > > >
> > > > > ---------- Patch content --------
> > > > >
> > > > > Modern processors has multiple way instruction decoders
> > > > > For x86, icelake/zen3 has 5 uops, so for small loop with <= 4
> > > > > instructions (usually has 3 uops with a cmp/jmp pair that can be
> > > > > macro-fused), the decoder would have 2 uops bubble for each iteration
> > > > > and the pipeline could not be fully utilized.
> > > > >
> > > > > Therefore, this patch enables loop unrolling for small size loop at O2
> > > > > to fullfill the decoder as much as possible. It turns on rtl loop
> > > > > unrolling when targetm.loop_unroll_adjust exists and O2 plus speed only.
> > > > > In x86 backend the default behavior is to unroll small loops with less
> > > > > than 4 insns by 1 time.
> > > > >
> > > > > This improves 548.exchange2 by 9% on icelake and 7.4% on zen3 with
> > > > > 0.9% 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.
> > > > >
> > > > > gcc/ChangeLog:
> > > > >
> > > > >         * common/config/i386/i386-common.cc (ix86_optimization_table):
> > > > >         Enable small loop unroll at O2 by default.
> > > > >         * config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
> > > > >         factor if -munroll-only-small-loops enabled and -funroll-loops/
> > > > >         -funroll-all-loops are disabled.
> > > > >         * 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.
> > > > >         * loop-init.cc (pass_rtl_unroll_loops::gate): Enable rtl
> > > > >         loop unrolling for -O2-speed and above if target hook
> > > > >         loop_unroll_adjust exists.
> > > > >
> > > > > gcc/testsuite/ChangeLog:
> > > > >
> > > > >         * gcc.dg/guality/loop-1.c: Add additional option
> > > > >           -mno-unroll-only-small-loops.
> > > > >         * gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
> > > > >         * gcc.target/i386/pr93002.c: Likewise.
> > > > > ---
> > > > >  gcc/common/config/i386/i386-common.cc   |  1 +
> > > > >  gcc/config/i386/i386.cc                 | 18 ++++++++++++++++++
> > > > >  gcc/config/i386/i386.opt                | 13 +++++++++++++
> > > > >  gcc/doc/invoke.texi                     | 16 ++++++++++++++++
> > > > >  gcc/loop-init.cc                        | 10 +++++++---
> > > > >  gcc/testsuite/gcc.dg/guality/loop-1.c   |  2 ++
> > > > >  gcc/testsuite/gcc.target/i386/pr86270.c |  2 +-
> > > > >  gcc/testsuite/gcc.target/i386/pr93002.c |  2 +-
> > > > >  8 files changed, 59 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/gcc/common/config/i386/i386-common.cc b/gcc/common/config/i386/i386-common.cc
> > > > > index f66bdd5a2af..c6891486078 100644
> > > > > --- a/gcc/common/config/i386/i386-common.cc
> > > > > +++ b/gcc/common/config/i386/i386-common.cc
> > > > > @@ -1724,6 +1724,7 @@ 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_munroll_only_small_loops, NULL, 1 },
> > > > >      /* 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.cc b/gcc/config/i386/i386.cc
> > > > > index c0f37149ed0..0f94a3b609e 100644
> > > > > --- a/gcc/config/i386/i386.cc
> > > > > +++ b/gcc/config/i386/i386.cc
> > > > > @@ -23827,6 +23827,24 @@ 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 (!(flag_unroll_loops
> > > > > +       || flag_unroll_all_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))
> > > > > +       if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)
> > > >
> > > > either add braces or combine the two if's
> > > >
> > > > Otherwise the middle-end changes look OK.  The target maintainers need to decide
> > > > whether the two --params should be core tunings instead - I would assume that
> > > > given your rationale the decode and issue widths of the core plays an important
> > > > role here.  That might also suggest a single parameter instead and unrolling
> > > > (factor * issue_width) / loop->ninsns times instead of a static unroll_factor?
> > > Although ix86_small_unroll_insns is coming from issue_rate, it's tuned
> > > for codesize.
> > > Make it exact as issue_rate and using factor * issue_width /
> > > loop->ninsns may increase code size too much.
> > > So I prefer to add those 2 parameters to the cost table for core
> > > tunings instead of 1.
> > > >
> > > > Thanks,
> > > > Richard.
> > > >
> > > > > +         nunroll = (unsigned) ix86_small_unroll_factor;
> > > > > +
> > > > > +      return nunroll;
> > > > > +    }
> > > > > +
> > > > >    if (!TARGET_ADJUST_UNROLL)
> > > > >       return nunroll;
> > > > >
> > > > > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > > > > index 53d534f6392..6da9c8d670d 100644
> > > > > --- a/gcc/config/i386/i386.opt
> > > > > +++ b/gcc/config/i386/i386.opt
> > > > > @@ -1224,3 +1224,16 @@ mavxvnniint8
> > > > >  Target Mask(ISA2_AVXVNNIINT8) Var(ix86_isa_flags2) Save
> > > > >  Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2 and
> > > > >  AVXVNNIINT8 built-in functions and code generation.
> > > > > +
> > > > > +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 550aec87809..487218bd0ce 100644
> > > > > --- a/gcc/doc/invoke.texi
> > > > > +++ b/gcc/doc/invoke.texi
> > > > > @@ -15821,6 +15821,14 @@ 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
> > > > > @@ -25232,6 +25240,14 @@ 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. Explicit
> > > > > +-f[no-]unroll-[all-]loops would disable this flag to avoid any
> > > > > +unintended unrolling behavior that user does not want.
> > > > >  @end table
> > > > >
> > > > >  @node M32C Options
> > > > > diff --git a/gcc/loop-init.cc b/gcc/loop-init.cc
> > > > > index b9e07973dd6..9789efa1e11 100644
> > > > > --- a/gcc/loop-init.cc
> > > > > +++ b/gcc/loop-init.cc
> > > > > @@ -565,9 +565,12 @@ public:
> > > > >    {}
> > > > >
> > > > >    /* opt_pass methods: */
> > > > > -  bool gate (function *) final override
> > > > > +  bool gate (function *fun) final override
> > > > >      {
> > > > > -      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll);
> > > > > +      return (flag_unroll_loops || flag_unroll_all_loops || cfun->has_unroll
> > > > > +             || (targetm.loop_unroll_adjust
> > > > > +                 && optimize >= 2
> > > > > +                 && optimize_function_for_speed_p (fun)));
> > > > >      }
> > > > >
> > > > >    unsigned int execute (function *) final override;
> > > > > @@ -583,7 +586,8 @@ pass_rtl_unroll_loops::execute (function *fun)
> > > > >        if (dump_file)
> > > > >         df_dump (dump_file);
> > > > >
> > > > > -      if (flag_unroll_loops)
> > > > > +      if (flag_unroll_loops
> > > > > +         || targetm.loop_unroll_adjust)
> > > > >         flags |= UAP_UNROLL;
> > > > >        if (flag_unroll_all_loops)
> > > > >         flags |= UAP_UNROLL_ALL;
> > > > > diff --git a/gcc/testsuite/gcc.dg/guality/loop-1.c b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > > > index 1b1f6d32271..a32ea445a3f 100644
> > > > > --- a/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > > > +++ b/gcc/testsuite/gcc.dg/guality/loop-1.c
> > > > > @@ -1,5 +1,7 @@
> > > > >  /* { dg-do run } */
> > > > >  /* { dg-options "-fno-tree-scev-cprop -fno-tree-vectorize -g" } */
> > > > > +/* { dg-additional-options "-mno-unroll-only-small-loops" { target ia32 } } */
> > > > > +
> > > > >
> > > > >  #include "../nop.h"
> > > > >
> > > > > 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
> > > > >
> > >
> > >
> > >
> > > --
> > > BR,
> > > Hongtao
>
>
>
> --
> BR,
> Hongtao