From f200c56787f2c6f93ffb739d57d01a294ab72f68 Mon Sep 17 00:00:00 2001 From: Philipp Tomsich Date: Thu, 23 Mar 2023 19:47:57 +0100 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. This commit: * adds a new tuning option AARCH64_EXTRA_TUNE_NO_LDP_COMBINE * allows -moverride=tune=... to override this These changes are benchmark-driven, yielding the following changes (with a net-overall improvement): 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% 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/testsuite/ChangeLog: * gcc.target/aarch64/ampere1-no_ldp_combine.c: New test. --- gcc/config/aarch64/aarch64-tuning-flags.def | 3 +++ gcc/config/aarch64/aarch64.cc | 18 ++++++++++++++++-- .../gcc.target/aarch64/ampere1-no_ldp_combine.c | 11 +++++++++++ 3 files changed, 30 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.target/aarch64/ampere1-no_ldp_combine.c diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def b/gcc/config/aarch64/aarch64-tuning-flags.def index 712895a..52112ba 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 f4ef22c..0f04ab9 100644 --- a/gcc/config/aarch64/aarch64.cc +++ b/gcc/config/aarch64/aarch64.cc @@ -1933,7 +1933,7 @@ static const struct tune_params ampere1_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. */ &ere1_prefetch_tune }; @@ -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. */ &ere1_prefetch_tune }; @@ -26053,6 +26053,20 @@ 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). + TODO: Implement fine-grained tuning control for LDP and STP: + 1. control policies for load and store separately; + 2. support the following policies: + - default (use what is in the tuning structure) + - always + - never + - aligned (only if the compiler can prove that the + load will be aligned to 2 * element_size) */ + if (load && (aarch64_tune_params.extra_tuning_flags + & AARCH64_EXTRA_TUNE_NO_LDP_COMBINE)) + return false; + if (load) { mem_1 = operands[1]; diff --git a/gcc/testsuite/gcc.target/aarch64/ampere1-no_ldp_combine.c b/gcc/testsuite/gcc.target/aarch64/ampere1-no_ldp_combine.c new file mode 100644 index 0000000..bc871f4 --- /dev/null +++ b/gcc/testsuite/gcc.target/aarch64/ampere1-no_ldp_combine.c @@ -0,0 +1,11 @@ +/* { dg-options "-O3 -mtune=ampere1" } */ + +long +foo (long a[]) +{ + return a[0] + a[1]; +} + +/* We should see two ldrs instead of one ldp. */ +/* { dg-final { scan-assembler {\tldr\t} } } */ +/* { dg-final { scan-assembler-not {\tldp\t} } } */ -- 2.7.4