RE: [PATCH] i386: Only enable small loop unrolling in backend [PR 107602]

["Liu, Hongtao" <hongtao.liu@intel.com>]

> -----Original Message-----
> From: Wang, Hongyu <hongyu.wang@intel.com>
> Sent: Saturday, November 19, 2022 2:26 PM
> To: gcc-patches@gcc.gnu.org
> Cc: richard.guenther@gmail.com; ubizjak@gmail.com; Liu, Hongtao
> <hongtao.liu@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
> 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