Victor Do Nascimento <victor.donascime...@arm.com> writes:
> The armv9.4-a architectural revision adds three new atomic operations
> associated with the LSE128 feature:
>
> * LDCLRP - Atomic AND NOT (bitclear) of a location with 128-bit
> value held in a pair of registers, with original data loaded into
> the same 2 registers.
> * LDSETP - Atomic OR (bitset) of a location with 128-bit value held
> in a pair of registers, with original data loaded into the same 2
> registers.
> * SWPP - Atomic swap of one 128-bit value with 128-bit value held
> in a pair of registers.
>
> This patch adds the logic required to make use of these when the
> architectural feature is present and a suitable assembler available.
>
> In order to do this, the following changes are made:
>
> 1. Add a configure-time check to check for LSE128 support in the
> assembler.
> 2. Edit host-config.h so that when N == 16, nifunc = 2.
> 3. Where available due to LSE128, implement the second ifunc, making
> use of the novel instructions.
> 4. For atomic functions unable to make use of these new
> instructions, define a new alias which causes the _i1 function
> variant to point ahead to the corresponding _i2 implementation.
>
> libatomic/ChangeLog:
>
> * Makefile.am (AM_CPPFLAGS): add conditional setting of
> -DHAVE_FEAT_LSE128.
> * acinclude.m4 (LIBAT_TEST_FEAT_LSE128): New.
> * config/linux/aarch64/atomic_16.S (LSE128): New macro
> definition.
> (libat_exchange_16): New LSE128 variant.
> (libat_fetch_or_16): Likewise.
> (libat_or_fetch_16): Likewise.
> (libat_fetch_and_16): Likewise.
> (libat_and_fetch_16): Likewise.
> * config/linux/aarch64/host-config.h (IFUNC_COND_2): New.
> (IFUNC_NCOND): Add operand size checking.
> (has_lse2): Renamed from `ifunc1`.
> (has_lse128): New.
> (HAS_LSE128): Likewise.
> * libatomic/configure.ac: Add call to LIBAT_TEST_FEAT_LSE128.
> * configure (ac_subst_vars): Regenerated via autoreconf.
> * libatomic/Makefile.in: Likewise.
> * libatomic/auto-config.h.in: Likewise.
> ---
> libatomic/Makefile.am | 3 +
> libatomic/Makefile.in | 1 +
> libatomic/acinclude.m4 | 19 +++
> libatomic/auto-config.h.in | 3 +
> libatomic/config/linux/aarch64/atomic_16.S | 170 ++++++++++++++++++-
> libatomic/config/linux/aarch64/host-config.h | 29 +++-
> libatomic/configure | 59 ++++++-
> libatomic/configure.ac | 1 +
> 8 files changed, 276 insertions(+), 9 deletions(-)
>
> [...]
> diff --git a/libatomic/acinclude.m4 b/libatomic/acinclude.m4
> index f35ab5b60a5..4197db8f404 100644
> --- a/libatomic/acinclude.m4
> +++ b/libatomic/acinclude.m4
> @@ -83,6 +83,25 @@ AC_DEFUN([LIBAT_TEST_ATOMIC_BUILTIN],[
> ])
> ])
>
> +dnl
> +dnl Test if the host assembler supports armv9.4-a LSE128 isns.
> +dnl
> +AC_DEFUN([LIBAT_TEST_FEAT_LSE128],[
> + AC_CACHE_CHECK([for armv9.4-a LSE128 insn support],
> + [libat_cv_have_feat_lse128],[
> + AC_LANG_CONFTEST([AC_LANG_PROGRAM([],[asm(".arch armv9-a+lse128")])])
> + if AC_TRY_EVAL(ac_link); then
ac_compile should be enough for this. The link step isn't really
adding anything.
> + eval libat_cv_have_feat_lse128=yes
> + else
> + eval libat_cv_have_feat_lse128=no
> + fi
> + rm -f conftest*
> + ])
> + LIBAT_DEFINE_YESNO([HAVE_FEAT_LSE128], [$libat_cv_have_feat_lse128],
> + [Have LSE128 support for 16 byte integers.])
> + AM_CONDITIONAL([ARCH_AARCH64_HAVE_LSE128], [test
> x$libat_cv_have_feat_lse128 = xyes])
> +])
> +
> dnl
> dnl Test if we have __atomic_load and __atomic_store for mode $1, size $2
> dnl
> [...]
> @@ -206,6 +211,31 @@ ENTRY (libat_exchange_16)
> END (libat_exchange_16)
>
>
> +#if HAVE_FEAT_LSE128
> +ENTRY_FEAT (libat_exchange_16, LSE128)
> + mov tmp0, x0
> + mov res0, in0
> + mov res1, in1
> + cbnz w4, 1f
> +
> + /* RELAXED. */
> + swpp res0, res1, [tmp0]
> + ret
> +1:
> + cmp w4, ACQUIRE
> + b.hi 2f
> +
> + /* ACQUIRE/CONSUME. */
> + swppa res0, res1, [tmp0]
> + ret
> +
> + /* RELEASE/ACQ_REL/SEQ_CST. */
> +2: swppal res0, res1, [tmp0]
> + ret
> +END_FEAT (libat_exchange_16, LSE128)
> +#endif
Is there no benefit to using SWPPL for RELEASE here? Similarly for the
others.
Looks good otherwise.
Thanks,
Richard
