Re: [PATCH] riscv: Add support for XTheadBb in string-fz[a,i].h

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 23/08/23 02:46, Christoph Muellner wrote:
> From: Christoph Müllner <christoph.muellner@vrull.eu>
> 
> XTheadBb has similar instructions like Zbb, which allow optimized
> string processing:
> * th.ff0: find-first zero is a CLZ instruction.
> * th.tstnbz: Similar like orc.b, but with a bit-inverted result.
> 
> The instructions are documented here:
>   https://github.com/T-head-Semi/thead-extension-spec/tree/master/xtheadbb
> 
> These instructions can be found in the T-Head C906 and the C910.
> 
> Tested with the string tests.
> 
> Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>


LGTM, thanks.  Is th.tstnbz available as builtin by chance?

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>


> ---
>  sysdeps/riscv/string-fza.h | 7 ++++++-
>  sysdeps/riscv/string-fzi.h | 2 +-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/sysdeps/riscv/string-fza.h b/sysdeps/riscv/string-fza.h
> index 4429653a00..4958d5d151 100644
> --- a/sysdeps/riscv/string-fza.h
> +++ b/sysdeps/riscv/string-fza.h
> @@ -19,7 +19,7 @@
>  #ifndef _RISCV_STRING_FZA_H
>  #define _RISCV_STRING_FZA_H 1
>  
> -#ifdef __riscv_zbb
> +#if defined __riscv_zbb || defined __riscv_xtheadbb
>  /* With bitmap extension we can use orc.b to find all zero bytes.  */
>  # include <string-misc.h>
>  # include <string-optype.h>
> @@ -32,8 +32,13 @@ static __always_inline find_t
>  find_zero_all (op_t x)
>  {
>    find_t r;
> +#ifdef __riscv_xtheadbb
> +  asm ("th.tstnbz %0, %1" : "=r" (r) : "r" (x));
> +  return r;
> +#else
>    asm ("orc.b %0, %1" : "=r" (r) : "r" (x));
>    return ~r;
> +#endif
>  }
>  
>  /* This function returns 0xff for each byte that is equal between X1 and
> diff --git a/sysdeps/riscv/string-fzi.h b/sysdeps/riscv/string-fzi.h
> index 8f56c378ff..45d6367a10 100644
> --- a/sysdeps/riscv/string-fzi.h
> +++ b/sysdeps/riscv/string-fzi.h
> @@ -19,7 +19,7 @@
>  #ifndef _STRING_RISCV_FZI_H
>  #define _STRING_RISCV_FZI_H 1
>  
> -#ifdef __riscv_zbb
> +#if defined __riscv_zbb || defined __riscv_xtheadbb
>  # include <sysdeps/generic/string-fzi.h>
>  #else
>  /* Without bitmap clz/ctz extensions, it is faster to direct test the bits