On Thu, Apr 12, 2012 at 3:16 PM, Richard Guenther <richard.guent...@gmail.com> wrote: > On Thu, Apr 12, 2012 at 1:05 PM, Igor Zamyatin <izamya...@gmail.com> wrote: >> On Wed, Apr 11, 2012 at 12:39 PM, Richard Guenther >> <richard.guent...@gmail.com> wrote: >>> On Tue, Apr 10, 2012 at 8:43 PM, Igor Zamyatin <izamya...@gmail.com> wrote: >>>> Hi All! >>>> >>>> Here is a patch that enables unroll at O2 for Atom. >>>> >>>> This gives good performance boost on EEMBC 2.0 (~+8% in Geomean for 32 >>>> bits) with quite moderate code size increase (~5% for EEMBC2.0, 32 >>>> bits). >>> >>> 5% is not moderate. Your patch does enable unrolling at -O2 but not -O3, >>> why? Why do you disable register renaming? check_imull requires a function >>> comment. >> >> Sure, enabling unroll for O3 could be the next step. >> We can't avoid code size increase with unroll - what number do you >> think will be appropriate? >> Register renaming was the reason of several degradations during tuning >> process >> Comment for check_imull was added >> >>> >>> This completely looks like a hack for EEMBC2.0, so it's definitely not ok. >> >> Why? EEMBC was measured and result provided here just because this >> benchmark considers to be very relevant for Atom > > I'd say that SPEC INT (2000 / 2006) is more relevant for Atom (SPEC FP > would be irrelevant OTOH). Similar code size for, say, Mozilla Firefox > or GCC itself would be important. > >>> -O2 is not supposed to give best benchmark results. >> >> O2 is wide-used so performance improvement could be important for users. > > But not at a 5% size cost. Please also always check the compile-time effect > which is important for -O2 as well.
What would be an acceptable number of size cost/compile-time increase for O2 and O3 on EEMBC, SPEC INT 2000 and Mozilla? Is it possible in common to put Atom-specific unroll heuristics under some option which could be mentioned in GCC docs? > > Richard. > >>> >>> Thanks, >>> Richard. >>> >>>> >>>> Tested for i386 and x86-64, ok for trunk? >> >> Updated patch attached >> >>>> >>>> Thanks, >>>> Igor >>>> >>>> ChangeLog: >>>> >>>> 2012-04-10 Yakovlev Vladimir <vladimir.b.yakov...@intel.com> >>>> >>>> * gcc/config/i386/i386.c (check_imul): New routine. >>>> (ix86_loop_unroll_adjust): New target hook. >>>> (ix86_option_override_internal): Enable unrolling on Atom at -O2. >>>> (TARGET_LOOP_UNROLL_ADJUST): New define. Thanks, Igor
