Re: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1
On Fri, 14 Apr 2023 at 13:02, Kyrylo Tkachov wrote: > Hi Philipp, > > From: Philipp Tomsich > Sent: Friday, April 14, 2023 11:26 AM > To: Kyrylo Tkachov > Cc: gcc-patches@gcc.gnu.org; Di Zhao > Subject: Re: [PATCH] aarch64: disable LDP via tuning structure for > -mcpu=ampere1 > > > > On Fri, 14 Apr 2023 at 11:31, Philipp Tomsich philipp.toms...@vrull.eu> wrote: > Kyrylo, > > On Fri, 14 Apr 2023 at 11:21, Kyrylo Tkachov kyrylo.tkac...@arm.com> wrote: > > > > Hi Philipp, > > > > > -Original Message- > > > From: Philipp Tomsich <mailto:philipp.toms...@vrull.eu> > > > Sent: Friday, April 14, 2023 12:22 AM > > > To: mailto:gcc-patches@gcc.gnu.org > > > Cc: Kyrylo Tkachov <mailto:kyrylo.tkac...@arm.com>; Philipp Tomsich > > > <mailto:philipp.toms...@vrull.eu>; Di Zhao di.z...@amperecomputing.com> > > > Subject: [PATCH] aarch64: disable LDP via tuning structure for - > > > mcpu=ampere1 > > > > > > AmpereOne (-mcpu=ampere1) breaks LDP instructions into two uops. > > > Given the chance that this causes instructions to slip into the next > > > decoding cycle and the additional overheads when handling > > > cacheline-crossing LDP instructions, we disable the generation of LDP > > > isntructions through the tuning structure from instruction combining > > > (such as in peephole2). > > > > > > Given the code-density benefits in builtins and prologue/epilogue > > > expansion, we allow LDPs there. > > > > LDPs are indeed quite an important part of the ISA for code density and > there are, in principle, second-order benefits from using them, like > keeping the instruction cache footprint low (which can be important for > large workloads). > > Did you gather some benchmarks showing a benefit of disabling them in > this manner? > > >This has been benchmark-driven, but I need to follow up separately (as > >I the final numbers are with the folks that have access to the > >benchmark machines).. > > >Here are the numbers for the submitted change for AmpereOne: > > 503.bwaves_r.-0.88% > > 507.cactuBSSN_r0.35% > > 508.namd_r 3.09% > > 510.parest_r -2.99% > > 511.povray_r5.54% > > 519.lbm_r 15.83% > > 521.wrf_r 0.56% > > 526.blender_r 2.47% > > 527.cam4_r 0.70% > > 538.imagick_r 0.00% > > 544.nab_r-0.33% > > 549.fotonik3d_r. -0.42% > > 554.roms_r 0.00% > > = total 1.79% > > Thanks for getting these, the gains are quite significant. > > > > > > This commit: > > > * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE > > > * allows -moverride=tune=... to override this > > > > > > Signed-off-by: Philipp Tomsich <mailto:philipp.toms...@vrull.eu> > > > Co-Authored-By: Di Zhao <mailto:di.z...@amperecomputing.com> > > > > > > gcc/ChangeLog: > > > > > > * config/aarch64/aarch64-tuning-flags.def > > > (AARCH64_EXTRA_TUNING_OPTION): > > > Add AARCH64_EXTRA_TUNE_NO_LDP_COMBINE. > > > * config/aarch64/aarch64.cc (aarch64_operands_ok_for_ldpstp): > > > Check for the above tuning option when processing loads. > > > > > > --- > > > > > > gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ > > > gcc/config/aarch64/aarch64.cc | 8 +++- > > > 2 files changed, 10 insertions(+), 1 deletion(-) > > > > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def > > > b/gcc/config/aarch64/aarch64-tuning-flags.def > > > index 712895a5263..52112ba7c48 100644 > > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def > > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def > > > @@ -44,6 +44,9 @@ AARCH64_EXTRA_TUNING_OPTION > > > ("cheap_shift_extend", CHEAP_SHIFT_EXTEND) > > > /* Disallow load/store pair instructions on Q-registers. */ > > > AARCH64_EXTRA_TUNING_OPTION ("no_ldp_stp_qregs", > > > NO_LDP_STP_QREGS) > > > > > > +/* Disallow load-pair instructions to be formed in combine/peephole. > */ > > > +AARCH64_EXTRA_TUNING_OPTION ("no_ldp_combine", > > > NO_LDP_COMBINE) > > > + > > > AARCH64_EXTRA_TUNING_OPTION ("rename_load_regs", > > > RENAME_LOAD_REGS) > > > > > > AARCH64_EXTR
RE: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1
Hi Philipp, From: Philipp Tomsich Sent: Friday, April 14, 2023 11:26 AM To: Kyrylo Tkachov Cc: gcc-patches@gcc.gnu.org; Di Zhao Subject: Re: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1 On Fri, 14 Apr 2023 at 11:31, Philipp Tomsich <mailto:philipp.toms...@vrull.eu> wrote: Kyrylo, On Fri, 14 Apr 2023 at 11:21, Kyrylo Tkachov <mailto:kyrylo.tkac...@arm.com> wrote: > > Hi Philipp, > > > -Original Message- > > From: Philipp Tomsich <mailto:philipp.toms...@vrull.eu> > > Sent: Friday, April 14, 2023 12:22 AM > > To: mailto:gcc-patches@gcc.gnu.org > > Cc: Kyrylo Tkachov <mailto:kyrylo.tkac...@arm.com>; Philipp Tomsich > > <mailto:philipp.toms...@vrull.eu>; Di Zhao > > <mailto:di.z...@amperecomputing.com> > > Subject: [PATCH] aarch64: disable LDP via tuning structure for - > > mcpu=ampere1 > > > > AmpereOne (-mcpu=ampere1) breaks LDP instructions into two uops. > > Given the chance that this causes instructions to slip into the next > > decoding cycle and the additional overheads when handling > > cacheline-crossing LDP instructions, we disable the generation of LDP > > isntructions through the tuning structure from instruction combining > > (such as in peephole2). > > > > Given the code-density benefits in builtins and prologue/epilogue > > expansion, we allow LDPs there. > > LDPs are indeed quite an important part of the ISA for code density and there > are, in principle, second-order benefits from using them, like keeping the > instruction cache footprint low (which can be important for large workloads). > Did you gather some benchmarks showing a benefit of disabling them in this > manner? >This has been benchmark-driven, but I need to follow up separately (as >I the final numbers are with the folks that have access to the >benchmark machines).. >Here are the numbers for the submitted change for AmpereOne: > 503.bwaves_r. -0.88% > 507.cactuBSSN_r 0.35% > 508.namd_r 3.09% > 510.parest_r -2.99% > 511.povray_r 5.54% > 519.lbm_r 15.83% > 521.wrf_r 0.56% > 526.blender_r 2.47% > 527.cam4_r 0.70% > 538.imagick_r 0.00% > 544.nab_r -0.33% > 549.fotonik3d_r. -0.42% > 554.roms_r 0.00% > = total 1.79% Thanks for getting these, the gains are quite significant. > > > This commit: > > * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE > > * allows -moverride=tune=... to override this > > > > Signed-off-by: Philipp Tomsich <mailto:philipp.toms...@vrull.eu> > > Co-Authored-By: Di Zhao <mailto:di.z...@amperecomputing.com> > > > > gcc/ChangeLog: > > > > * config/aarch64/aarch64-tuning-flags.def > > (AARCH64_EXTRA_TUNING_OPTION): > > Add AARCH64_EXTRA_TUNE_NO_LDP_COMBINE. > > * config/aarch64/aarch64.cc (aarch64_operands_ok_for_ldpstp): > > Check for the above tuning option when processing loads. > > > > --- > > > > gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ > > gcc/config/aarch64/aarch64.cc | 8 +++- > > 2 files changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def > > b/gcc/config/aarch64/aarch64-tuning-flags.def > > index 712895a5263..52112ba7c48 100644 > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def > > @@ -44,6 +44,9 @@ AARCH64_EXTRA_TUNING_OPTION > > ("cheap_shift_extend", CHEAP_SHIFT_EXTEND) > > /* Disallow load/store pair instructions on Q-registers. */ > > AARCH64_EXTRA_TUNING_OPTION ("no_ldp_stp_qregs", > > NO_LDP_STP_QREGS) > > > > +/* Disallow load-pair instructions to be formed in combine/peephole. */ > > +AARCH64_EXTRA_TUNING_OPTION ("no_ldp_combine", > > NO_LDP_COMBINE) > > + > > AARCH64_EXTRA_TUNING_OPTION ("rename_load_regs", > > RENAME_LOAD_REGS) > > > > AARCH64_EXTRA_TUNING_OPTION ("cse_sve_vl_constants", > > CSE_SVE_VL_CONSTANTS) > > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc > > index f4ef22ce02f..8dc1a9ceb17 100644 > > --- a/gcc/config/aarch64/aarch64.cc > > +++ b/gcc/config/aarch64/aarch64.cc > > @@ -1971,7 +1971,7 @@ static const struct tune_params ampere1a_tunings > > = > > 2, /* min_div_recip_mul_df. */ > > 0, /* max_case_values. */ > > tune
Re: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1
On Fri, 14 Apr 2023 at 11:31, Philipp Tomsich wrote: > Kyrylo, > > On Fri, 14 Apr 2023 at 11:21, Kyrylo Tkachov > wrote: > > > > Hi Philipp, > > > > > -Original Message- > > > From: Philipp Tomsich > > > Sent: Friday, April 14, 2023 12:22 AM > > > To: gcc-patches@gcc.gnu.org > > > Cc: Kyrylo Tkachov ; Philipp Tomsich > > > ; Di Zhao > > > Subject: [PATCH] aarch64: disable LDP via tuning structure for - > > > mcpu=ampere1 > > > > > > AmpereOne (-mcpu=ampere1) breaks LDP instructions into two uops. > > > Given the chance that this causes instructions to slip into the next > > > decoding cycle and the additional overheads when handling > > > cacheline-crossing LDP instructions, we disable the generation of LDP > > > isntructions through the tuning structure from instruction combining > > > (such as in peephole2). > > > > > > Given the code-density benefits in builtins and prologue/epilogue > > > expansion, we allow LDPs there. > > > > LDPs are indeed quite an important part of the ISA for code density and > there are, in principle, second-order benefits from using them, like > keeping the instruction cache footprint low (which can be important for > large workloads). > > Did you gather some benchmarks showing a benefit of disabling them in > this manner? > > This has been benchmark-driven, but I need to follow up separately (as > I the final numbers are with the folks that have access to the > benchmark machines).. > Here are the numbers for the submitted change for AmpereOne: 503.bwaves_r.-0.88% 507.cactuBSSN_r0.35% 508.namd_r 3.09% 510.parest_r -2.99% 511.povray_r5.54% 519.lbm_r 15.83% 521.wrf_r 0.56% 526.blender_r 2.47% 527.cam4_r 0.70% 538.imagick_r 0.00% 544.nab_r-0.33% 549.fotonik3d_r. -0.42% 554.roms_r 0.00% = total 1.79% > > > > > This commit: > > > * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE > > > * allows -moverride=tune=... to override this > > > > > > Signed-off-by: Philipp Tomsich > > > Co-Authored-By: Di Zhao > > > > > > gcc/ChangeLog: > > > > > > * config/aarch64/aarch64-tuning-flags.def > > > (AARCH64_EXTRA_TUNING_OPTION): > > > Add AARCH64_EXTRA_TUNE_NO_LDP_COMBINE. > > > * config/aarch64/aarch64.cc (aarch64_operands_ok_for_ldpstp): > > > Check for the above tuning option when processing loads. > > > > > > --- > > > > > > gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ > > > gcc/config/aarch64/aarch64.cc | 8 +++- > > > 2 files changed, 10 insertions(+), 1 deletion(-) > > > > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def > > > b/gcc/config/aarch64/aarch64-tuning-flags.def > > > index 712895a5263..52112ba7c48 100644 > > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def > > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def > > > @@ -44,6 +44,9 @@ AARCH64_EXTRA_TUNING_OPTION > > > ("cheap_shift_extend", CHEAP_SHIFT_EXTEND) > > > /* Disallow load/store pair instructions on Q-registers. */ > > > AARCH64_EXTRA_TUNING_OPTION ("no_ldp_stp_qregs", > > > NO_LDP_STP_QREGS) > > > > > > +/* Disallow load-pair instructions to be formed in combine/peephole. > */ > > > +AARCH64_EXTRA_TUNING_OPTION ("no_ldp_combine", > > > NO_LDP_COMBINE) > > > + > > > AARCH64_EXTRA_TUNING_OPTION ("rename_load_regs", > > > RENAME_LOAD_REGS) > > > > > > AARCH64_EXTRA_TUNING_OPTION ("cse_sve_vl_constants", > > > CSE_SVE_VL_CONSTANTS) > > > diff --git a/gcc/config/aarch64/aarch64.cc > b/gcc/config/aarch64/aarch64.cc > > > index f4ef22ce02f..8dc1a9ceb17 100644 > > > --- a/gcc/config/aarch64/aarch64.cc > > > +++ b/gcc/config/aarch64/aarch64.cc > > > @@ -1971,7 +1971,7 @@ static const struct tune_params ampere1a_tunings > > > = > > >2, /* min_div_recip_mul_df. */ > > >0, /* max_case_values. */ > > >tune_params::AUTOPREFETCHER_WEAK, /* autoprefetcher_model. */ > > > - (AARCH64_EXTRA_TUNE_NONE), /* tune_flags. */ > > > + (AARCH64_EXTRA_TUNE_NO_LDP_COMBINE), /* tune_flags. */ > > >_prefetch_tune > > > }; > > > > > > @@ -26053,6 +26053,12 @@ aarch64_operands_ok_for_ldpstp (rtx > > > *operands, bool load, > > >enum reg_class rclass_1, rclass_2; > > >rtx mem_1, mem_2, reg_1, reg_2; > > > > > > + /* Allow the tuning structure to disable LDP instruction formation > > > + from combining instructions (e.g., in peephole2). */ > > > + if (load && (aarch64_tune_params.extra_tuning_flags > > > +& AARCH64_EXTRA_TUNE_NO_LDP_COMBINE)) > > > +return false; > > > > If we do decide to do this, I think this is not a complete approach. See > the similar tuning flag AARCH64_EXTRA_TUNE_NO_LDP_STP_QREGS. > > There's various other places in the backend that would need to be > adjusted to avoid bringing loads together for the peephole2s to merge (the > sched_fusion stuff). > >
Re: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1
For phase 1, we plan to replace this with a feature to allow finer-grained control over when to use LDP or STP (i.e., control these independently) with the following scopes and policies: - scopes are: { sched-fusion, mem, pro/epilogue, peephole } - policies are: { default (from tuning), always, never, aligned (to 2x element size) } Happy to get this fuller solution already onto the list, if it helps with forward-progress on the localised change. The current patch tries to be minimally invasive (i.e., it doesn't touch STP). It intentionally avoids modifying the sched-fusion logic (which requires refactoring, as it doesn't differentiate between the load and store cases), pro/epilogue creation and mem* function expansion. Philipp. On Fri, 14 Apr 2023 at 11:31, Philipp Tomsich wrote: > > Kyrylo, > > On Fri, 14 Apr 2023 at 11:21, Kyrylo Tkachov wrote: > > > > Hi Philipp, > > > > > -Original Message- > > > From: Philipp Tomsich > > > Sent: Friday, April 14, 2023 12:22 AM > > > To: gcc-patches@gcc.gnu.org > > > Cc: Kyrylo Tkachov ; Philipp Tomsich > > > ; Di Zhao > > > Subject: [PATCH] aarch64: disable LDP via tuning structure for - > > > mcpu=ampere1 > > > > > > AmpereOne (-mcpu=ampere1) breaks LDP instructions into two uops. > > > Given the chance that this causes instructions to slip into the next > > > decoding cycle and the additional overheads when handling > > > cacheline-crossing LDP instructions, we disable the generation of LDP > > > isntructions through the tuning structure from instruction combining > > > (such as in peephole2). > > > > > > Given the code-density benefits in builtins and prologue/epilogue > > > expansion, we allow LDPs there. > > > > LDPs are indeed quite an important part of the ISA for code density and > > there are, in principle, second-order benefits from using them, like > > keeping the instruction cache footprint low (which can be important for > > large workloads). > > Did you gather some benchmarks showing a benefit of disabling them in this > > manner? > > > This has been benchmark-driven, but I need to follow up separately (as > I the final numbers are with the folks that have access to the > benchmark machines).. > > > > > > This commit: > > > * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE > > > * allows -moverride=tune=... to override this > > > > > > Signed-off-by: Philipp Tomsich > > > Co-Authored-By: Di Zhao > > > > > > gcc/ChangeLog: > > > > > > * config/aarch64/aarch64-tuning-flags.def > > > (AARCH64_EXTRA_TUNING_OPTION): > > > Add AARCH64_EXTRA_TUNE_NO_LDP_COMBINE. > > > * config/aarch64/aarch64.cc (aarch64_operands_ok_for_ldpstp): > > > Check for the above tuning option when processing loads. > > > > > > --- > > > > > > gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ > > > gcc/config/aarch64/aarch64.cc | 8 +++- > > > 2 files changed, 10 insertions(+), 1 deletion(-) > > > > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def > > > b/gcc/config/aarch64/aarch64-tuning-flags.def > > > index 712895a5263..52112ba7c48 100644 > > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def > > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def > > > @@ -44,6 +44,9 @@ AARCH64_EXTRA_TUNING_OPTION > > > ("cheap_shift_extend", CHEAP_SHIFT_EXTEND) > > > /* Disallow load/store pair instructions on Q-registers. */ > > > AARCH64_EXTRA_TUNING_OPTION ("no_ldp_stp_qregs", > > > NO_LDP_STP_QREGS) > > > > > > +/* Disallow load-pair instructions to be formed in combine/peephole. */ > > > +AARCH64_EXTRA_TUNING_OPTION ("no_ldp_combine", > > > NO_LDP_COMBINE) > > > + > > > AARCH64_EXTRA_TUNING_OPTION ("rename_load_regs", > > > RENAME_LOAD_REGS) > > > > > > AARCH64_EXTRA_TUNING_OPTION ("cse_sve_vl_constants", > > > CSE_SVE_VL_CONSTANTS) > > > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc > > > index f4ef22ce02f..8dc1a9ceb17 100644 > > > --- a/gcc/config/aarch64/aarch64.cc > > > +++ b/gcc/config/aarch64/aarch64.cc > > > @@ -1971,7 +1971,7 @@ static const struct tune_params ampere1a_tunings > > > = > > >2, /* min_div_recip_mul_df. */ > > >0, /* max_case_values. */ > > >tune_params::AUTOPREFETCHER_WEAK, /* autoprefetcher_model. */ > > > - (AARCH64_EXTRA_TUNE_NONE), /* tune_flags. */ > > > + (AARCH64_EXTRA_TUNE_NO_LDP_COMBINE), /* tune_flags. */ > > >_prefetch_tune > > > }; > > > > > > @@ -26053,6 +26053,12 @@ aarch64_operands_ok_for_ldpstp (rtx > > > *operands, bool load, > > >enum reg_class rclass_1, rclass_2; > > >rtx mem_1, mem_2, reg_1, reg_2; > > > > > > + /* Allow the tuning structure to disable LDP instruction formation > > > + from combining instructions (e.g., in peephole2). */ > > > + if (load && (aarch64_tune_params.extra_tuning_flags > > > +& AARCH64_EXTRA_TUNE_NO_LDP_COMBINE)) > > > +return false; > > > > If we do decide to do this, I think this is not a complete approach. See > > the
Re: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1
Kyrylo, On Fri, 14 Apr 2023 at 11:21, Kyrylo Tkachov wrote: > > Hi Philipp, > > > -Original Message- > > From: Philipp Tomsich > > Sent: Friday, April 14, 2023 12:22 AM > > To: gcc-patches@gcc.gnu.org > > Cc: Kyrylo Tkachov ; Philipp Tomsich > > ; Di Zhao > > Subject: [PATCH] aarch64: disable LDP via tuning structure for - > > mcpu=ampere1 > > > > AmpereOne (-mcpu=ampere1) breaks LDP instructions into two uops. > > Given the chance that this causes instructions to slip into the next > > decoding cycle and the additional overheads when handling > > cacheline-crossing LDP instructions, we disable the generation of LDP > > isntructions through the tuning structure from instruction combining > > (such as in peephole2). > > > > Given the code-density benefits in builtins and prologue/epilogue > > expansion, we allow LDPs there. > > LDPs are indeed quite an important part of the ISA for code density and there > are, in principle, second-order benefits from using them, like keeping the > instruction cache footprint low (which can be important for large workloads). > Did you gather some benchmarks showing a benefit of disabling them in this > manner? This has been benchmark-driven, but I need to follow up separately (as I the final numbers are with the folks that have access to the benchmark machines).. > > > This commit: > > * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE > > * allows -moverride=tune=... to override this > > > > Signed-off-by: Philipp Tomsich > > Co-Authored-By: Di Zhao > > > > gcc/ChangeLog: > > > > * config/aarch64/aarch64-tuning-flags.def > > (AARCH64_EXTRA_TUNING_OPTION): > > Add AARCH64_EXTRA_TUNE_NO_LDP_COMBINE. > > * config/aarch64/aarch64.cc (aarch64_operands_ok_for_ldpstp): > > Check for the above tuning option when processing loads. > > > > --- > > > > gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ > > gcc/config/aarch64/aarch64.cc | 8 +++- > > 2 files changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def > > b/gcc/config/aarch64/aarch64-tuning-flags.def > > index 712895a5263..52112ba7c48 100644 > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def > > @@ -44,6 +44,9 @@ AARCH64_EXTRA_TUNING_OPTION > > ("cheap_shift_extend", CHEAP_SHIFT_EXTEND) > > /* Disallow load/store pair instructions on Q-registers. */ > > AARCH64_EXTRA_TUNING_OPTION ("no_ldp_stp_qregs", > > NO_LDP_STP_QREGS) > > > > +/* Disallow load-pair instructions to be formed in combine/peephole. */ > > +AARCH64_EXTRA_TUNING_OPTION ("no_ldp_combine", > > NO_LDP_COMBINE) > > + > > AARCH64_EXTRA_TUNING_OPTION ("rename_load_regs", > > RENAME_LOAD_REGS) > > > > AARCH64_EXTRA_TUNING_OPTION ("cse_sve_vl_constants", > > CSE_SVE_VL_CONSTANTS) > > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc > > index f4ef22ce02f..8dc1a9ceb17 100644 > > --- a/gcc/config/aarch64/aarch64.cc > > +++ b/gcc/config/aarch64/aarch64.cc > > @@ -1971,7 +1971,7 @@ static const struct tune_params ampere1a_tunings > > = > >2, /* min_div_recip_mul_df. */ > >0, /* max_case_values. */ > >tune_params::AUTOPREFETCHER_WEAK, /* autoprefetcher_model. */ > > - (AARCH64_EXTRA_TUNE_NONE), /* tune_flags. */ > > + (AARCH64_EXTRA_TUNE_NO_LDP_COMBINE), /* tune_flags. */ > >_prefetch_tune > > }; > > > > @@ -26053,6 +26053,12 @@ aarch64_operands_ok_for_ldpstp (rtx > > *operands, bool load, > >enum reg_class rclass_1, rclass_2; > >rtx mem_1, mem_2, reg_1, reg_2; > > > > + /* Allow the tuning structure to disable LDP instruction formation > > + from combining instructions (e.g., in peephole2). */ > > + if (load && (aarch64_tune_params.extra_tuning_flags > > +& AARCH64_EXTRA_TUNE_NO_LDP_COMBINE)) > > +return false; > > If we do decide to do this, I think this is not a complete approach. See the > similar tuning flag AARCH64_EXTRA_TUNE_NO_LDP_STP_QREGS. > There's various other places in the backend that would need to be adjusted to > avoid bringing loads together for the peephole2s to merge (the sched_fusion > stuff). > Plus there's the cpymem expansions that would generate load pairs too... I have add-on patches for these, but given that I don't have direct access to the benchmarking machine and the benchmarks have been run with this functionality only, I didn't submit them for the time being. Do you see a path to get this in during the current cycle and defer the add-on patches (happy to resubmit as a series) only? > We'd want some testcases added to check that LDPs are blocked too... > > Thanks, > Kyrill > > > + > >if (load) > > { > >mem_1 = operands[1]; > > -- > > 2.34.1 >
RE: [PATCH] aarch64: disable LDP via tuning structure for -mcpu=ampere1
Hi Philipp, > -Original Message- > From: Philipp Tomsich > Sent: Friday, April 14, 2023 12:22 AM > To: gcc-patches@gcc.gnu.org > Cc: Kyrylo Tkachov ; Philipp Tomsich > ; Di Zhao > Subject: [PATCH] aarch64: disable LDP via tuning structure for - > mcpu=ampere1 > > AmpereOne (-mcpu=ampere1) breaks LDP instructions into two uops. > Given the chance that this causes instructions to slip into the next > decoding cycle and the additional overheads when handling > cacheline-crossing LDP instructions, we disable the generation of LDP > isntructions through the tuning structure from instruction combining > (such as in peephole2). > > Given the code-density benefits in builtins and prologue/epilogue > expansion, we allow LDPs there. LDPs are indeed quite an important part of the ISA for code density and there are, in principle, second-order benefits from using them, like keeping the instruction cache footprint low (which can be important for large workloads). Did you gather some benchmarks showing a benefit of disabling them in this manner? > > This commit: > * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE > * allows -moverride=tune=... to override this > > Signed-off-by: Philipp Tomsich > Co-Authored-By: Di Zhao > > gcc/ChangeLog: > > * config/aarch64/aarch64-tuning-flags.def > (AARCH64_EXTRA_TUNING_OPTION): > Add AARCH64_EXTRA_TUNE_NO_LDP_COMBINE. > * config/aarch64/aarch64.cc (aarch64_operands_ok_for_ldpstp): > Check for the above tuning option when processing loads. > > --- > > gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ > gcc/config/aarch64/aarch64.cc | 8 +++- > 2 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def > b/gcc/config/aarch64/aarch64-tuning-flags.def > index 712895a5263..52112ba7c48 100644 > --- a/gcc/config/aarch64/aarch64-tuning-flags.def > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def > @@ -44,6 +44,9 @@ AARCH64_EXTRA_TUNING_OPTION > ("cheap_shift_extend", CHEAP_SHIFT_EXTEND) > /* Disallow load/store pair instructions on Q-registers. */ > AARCH64_EXTRA_TUNING_OPTION ("no_ldp_stp_qregs", > NO_LDP_STP_QREGS) > > +/* Disallow load-pair instructions to be formed in combine/peephole. */ > +AARCH64_EXTRA_TUNING_OPTION ("no_ldp_combine", > NO_LDP_COMBINE) > + > AARCH64_EXTRA_TUNING_OPTION ("rename_load_regs", > RENAME_LOAD_REGS) > > AARCH64_EXTRA_TUNING_OPTION ("cse_sve_vl_constants", > CSE_SVE_VL_CONSTANTS) > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc > index f4ef22ce02f..8dc1a9ceb17 100644 > --- a/gcc/config/aarch64/aarch64.cc > +++ b/gcc/config/aarch64/aarch64.cc > @@ -1971,7 +1971,7 @@ static const struct tune_params ampere1a_tunings > = >2, /* min_div_recip_mul_df. */ >0, /* max_case_values. */ >tune_params::AUTOPREFETCHER_WEAK, /* autoprefetcher_model. */ > - (AARCH64_EXTRA_TUNE_NONE), /* tune_flags. */ > + (AARCH64_EXTRA_TUNE_NO_LDP_COMBINE), /* tune_flags. */ >_prefetch_tune > }; > > @@ -26053,6 +26053,12 @@ aarch64_operands_ok_for_ldpstp (rtx > *operands, bool load, >enum reg_class rclass_1, rclass_2; >rtx mem_1, mem_2, reg_1, reg_2; > > + /* Allow the tuning structure to disable LDP instruction formation > + from combining instructions (e.g., in peephole2). */ > + if (load && (aarch64_tune_params.extra_tuning_flags > +& AARCH64_EXTRA_TUNE_NO_LDP_COMBINE)) > +return false; If we do decide to do this, I think this is not a complete approach. See the similar tuning flag AARCH64_EXTRA_TUNE_NO_LDP_STP_QREGS. There's various other places in the backend that would need to be adjusted to avoid bringing loads together for the peephole2s to merge (the sched_fusion stuff). Plus there's the cpymem expansions that would generate load pairs too... We'd want some testcases added to check that LDPs are blocked too... Thanks, Kyrill > + >if (load) > { >mem_1 = operands[1]; > -- > 2.34.1