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Re: [PATCH x86] Increase PARAM_MAX_COMPLETELY_PEELED_INSNS when branch is costly


> On Fri, Oct 10, 2014 at 5:40 PM, Evgeny Stupachenko <evstupac@gmail.com> wrote:
> > Hi,
> >
> > The patch increase PARAM_MAX_COMPLETELY_PEELED_INSNS for CPUs with
> > high branch cost.
> > Bootstrap and make check are in progress.
> > The patch boosts (up to 2,5 times improve) several benchmarks compiled
> > with "-Ofast" on Silvermont
> > Spec2000:
> > +5% gain on 173.applu
> > +1% gain on 255.vortex
> >
> > Is it ok for trunk when pass bootstrap and make check?
> 
> This is only a 20% increase - from 100 to 120.  I would instead suggest
> to explore doing this change unconditionally if it helps that much.

Agreed, I think the value of 100 was set decade ago by Zdenek and me completely
artifically. I do not recall any serious tuning of this flag.

Note that I plan to update
https://gcc.gnu.org/ml/gcc-patches/2013-11/msg02270.html to current tree so
PARAM_MAX_COMPLETELY_PEELED_INSNS will be used at gimple level rather than tree
changing its meaning somewhat.

Perhaps I could try to find time this or next week to update the patch so we do
not need to do the tuning twice.

Honza

> 
> Richard.
> 
> > Thanks,
> > Evgeny
> >
> > 2014-10-10  Evgeny Stupachenko  <evstupac@gmail.com>
> >         * config/i386/i386.c (ix86_option_override_internal): Increase
> >         PARAM_MAX_COMPLETELY_PEELED_INSNS for CPUs with high branch cost.
> >         * config/i386/i386.h (TARGET_HIGH_BRANCH_COST): New.
> >         * config/i386/x86-tune.def (X86_TUNE_HIGH_BRANCH_COST): Indicates
> >         CPUs with high branch cost.
> >
> > diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> > index 6337aa5..5ac10eb 100644
> > --- a/gcc/config/i386/i386.c
> > +++ b/gcc/config/i386/i386.c
> > @@ -4081,6 +4081,14 @@ ix86_option_override_internal (bool main_args_p,
> >                          opts->x_param_values,
> >                          opts_set->x_param_values);
> >
> > +  /* Extend full peel max insns parameter for CPUs with high branch cost.  */
> > +  if (TARGET_HIGH_BRANCH_COST)
> > +    maybe_set_param_value (PARAM_MAX_COMPLETELY_PEELED_INSNS,
> > +                          120,
> > +                          opts->x_param_values,
> > +                          opts_set->x_param_values);
> > +
> > +
> >    /* Enable sw prefetching at -O3 for CPUS that prefetching is helpful.  */
> >    if (opts->x_flag_prefetch_loop_arrays < 0
> >        && HAVE_prefetch
> > diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
> > index 2c64162..da0c57b 100644
> > --- a/gcc/config/i386/i386.h
> > +++ b/gcc/config/i386/i386.h
> > @@ -415,6 +415,7 @@ extern unsigned char ix86_tune_features[X86_TUNE_LAST];
> >  #define TARGET_INTER_UNIT_CONVERSIONS \
> >         ix86_tune_features[X86_TUNE_INTER_UNIT_CONVERSIONS]
> >  #define TARGET_FOUR_JUMP_LIMIT ix86_tune_features[X86_TUNE_FOUR_JUMP_LIMIT]
> > +#define TARGET_HIGH_BRANCH_COST
> > ix86_tune_features[X86_TUNE_HIGH_BRANCH_COST]
> >  #define TARGET_SCHEDULE                ix86_tune_features[X86_TUNE_SCHEDULE]
> >  #define TARGET_USE_BT          ix86_tune_features[X86_TUNE_USE_BT]
> >  #define TARGET_USE_INCDEC      ix86_tune_features[X86_TUNE_USE_INCDEC]
> > diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
> > index b6b210e..04d8bf8 100644
> > --- a/gcc/config/i386/x86-tune.def
> > +++ b/gcc/config/i386/x86-tune.def
> > @@ -208,6 +208,11 @@ DEF_TUNE (X86_TUNE_FOUR_JUMP_LIMIT, "four_jump_limit",
> >            m_PPRO | m_P4_NOCONA | m_BONNELL | m_SILVERMONT | m_INTEL |
> >           m_ATHLON_K8 | m_AMDFAM10)
> >
> > +/* X86_TUNE_HIGH_BRANCH_COST: Some CPUs have higher branch cost.  This could be
> > +   used to tune unroll, if-cvt, inline... heuristics.  */
> > +DEF_TUNE (X86_TUNE_HIGH_BRANCH_COST, "high_branch_cost",
> > +          m_BONNELL | m_SILVERMONT | m_INTEL)
> > +
> >  /*****************************************************************************/
> >  /* Integer instruction selection tuning                                      */
> >  /*****************************************************************************/


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