[PATCH v3] RISC-V: add multiarch RVV support for memcpy using FMV IFUNC

[Adhemerval Zanella Netto]

On 20/01/25 00:26, daichengrong@iscas.ac.cn wrote:
> From: daichengrong <daichengrong@iscas.ac.cn>
> 
> This patch introduces vector support for memcpy with IFUNC.
> The implementation select the RVV optimized memcpy version via hwprobe on kernel with RVV enabled.
> 
> Changes in v3:
>   Remove unnecessary whitespace
>   
> Changes in v2:
>   delete size-0 branch
> 
> Signed-off-by: daichengrong <daichengrong@iscas.ac.cn>

For performance improvements the usual way is to also provide some benchmark
numbers on real hardware (either using our synthetic benchtests or some other
benchmark that stresses the affected routines). 

Also, I take that RISCV_HWPROBE_IMA_V implies in RISCV_HWPROBE_MISALIGNED_FAST
right?

> ---
>  sysdeps/riscv/multiarch/memcpy_vector.S       | 35 +++++++++++++++++++
>  .../unix/sysv/linux/riscv/multiarch/Makefile  |  2 ++
>  .../unix/sysv/linux/riscv/multiarch/memcpy.c  |  5 +++
>  3 files changed, 42 insertions(+)
>  create mode 100644 sysdeps/riscv/multiarch/memcpy_vector.S
> 
> diff --git a/sysdeps/riscv/multiarch/memcpy_vector.S b/sysdeps/riscv/multiarch/memcpy_vector.S
> new file mode 100644
> index 0000000000..8fddab8432
> --- /dev/null
> +++ b/sysdeps/riscv/multiarch/memcpy_vector.S
> @@ -0,0 +1,35 @@
> +/* memcpy for RISC-V Vector.
> +   Copyright (C) 2024-2025 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +
> +#include <sysdep.h>
> +#include <sys/asm.h>
> +
> +ENTRY (__memcpy_vector)
> +    mv	    a6, a0
> +L(loop):
> +    vsetvli a3,a2,e8,m8,ta,mu
> +    vle8.v  v8,(a1)
> +    vse8.v  v8,(a6)
> +    add     a1,a1,a3
> +    sub     a2,a2,a3
> +    add     a6,a6,a3
> +    bnez    a2,L(loop)
> +L(ret):
> +    ret
> +END (__memcpy_vector)
> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
> index fcef5659d4..a8b6c22af1 100644
> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
> @@ -3,7 +3,9 @@ sysdep_routines += \
>    memcpy \
>    memcpy-generic \
>    memcpy_noalignment \
> +  memcpy_vector \
>    # sysdep_routines
>  
>  CFLAGS-memcpy_noalignment.c += -mno-strict-align
> +ASFLAGS-memcpy_vector.S += -march=rv64gcv
>  endif
> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> index 8544f5402a..105c837101 100644
> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> @@ -32,11 +32,16 @@ extern __typeof (__redirect_memcpy) __libc_memcpy;
>  
>  extern __typeof (__redirect_memcpy) __memcpy_generic attribute_hidden;
>  extern __typeof (__redirect_memcpy) __memcpy_noalignment attribute_hidden;
> +extern __typeof (__redirect_memcpy) __memcpy_vector attribute_hidden;
>  
>  static inline __typeof (__redirect_memcpy) *
>  select_memcpy_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func)
>  {
>    unsigned long long int v;
> +  if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_IMA_EXT_0, &v) == 0
> +      && (v & RISCV_HWPROBE_IMA_V) == RISCV_HWPROBE_IMA_V)
> +    return __memcpy_vector;
> +
>    if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_CPUPERF_0, &v) == 0
>        && (v & RISCV_HWPROBE_MISALIGNED_MASK) == RISCV_HWPROBE_MISALIGNED_FAST)
>      return __memcpy_noalignment;