Re: [PATCH 2/2] util/bufferiszero: Add simd acceleration for loongarch64

[Richard Henderson <richard.henderson@linaro.org>]

On 6/5/24 02:32, Bibo Mao wrote:
> Different gcc versions have different features, macro CONFIG_LSX_OPT
> and CONFIG_LASX_OPT is added here to detect whether gcc supports
> built-in lsx/lasx macro.
> 
> Function buffer_zero_lsx() is added for 128bit simd fpu optimization,
> and function buffer_zero_lasx() is for 256bit simd fpu optimization.
> 
> Loongarch gcc built-in lsx/lasx macro can be used only when compiler
> option -mlsx/-mlasx is added, and there is no separate compiler option
> for function only. So it is only in effect when qemu is compiled with
> parameter --extra-cflags="-mlasx"
> 
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
>   meson.build         |  11 +++++
>   util/bufferiszero.c | 103 ++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 114 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index 6386607144..29bc362d7a 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2855,6 +2855,17 @@ config_host_data.set('CONFIG_ARM_AES_BUILTIN', cc.compiles('''
>       void foo(uint8x16_t *p) { *p = vaesmcq_u8(*p); }
>     '''))
>   
> +# For Loongarch64, detect if LSX/LASX are available.
> + config_host_data.set('CONFIG_LSX_OPT', cc.compiles('''
> +    #include "lsxintrin.h"
> +    int foo(__m128i v) { return __lsx_bz_v(v); }
> +  '''))
> +
> +config_host_data.set('CONFIG_LASX_OPT', cc.compiles('''
> +    #include "lasxintrin.h"
> +    int foo(__m256i v) { return __lasx_xbz_v(v); }
> +  '''))

Both of these are introduced by gcc 14 and llvm 18, so I'm not certain of the utility of 
separate tests.  We might simplify this with

   config_host_data.set('CONFIG_LSX_LASX_INTRIN_H',
     cc.has_header('lsxintrin.h') && cc.has_header('lasxintrin.h'))


As you say, these headers require vector instructions to be enabled at compile-time rather 
than detecting them at runtime.  This is a point where the compilers could be improved to 
support __attribute__((target("xyz"))) and the builtins with that.  The i386 port does 
this, for instance.

In the meantime, it means that you don't need a runtime test.  Similar to aarch64 and the 
use of __ARM_NEON as a compile-time test for simd support.  Perhaps

#elif defined(CONFIG_LSX_LASX_INTRIN_H) && \
       (defined(__loongarch_sx) || defined(__loongarch_asx))
# ifdef __loongarch_sx
   ...
# endif
# ifdef __loongarch_asx
   ...
# endif


The actual code is perfectly fine, of course, since it follows the pattern from the 
others.  How much improvement do you see from bufferiszero-bench?


r~