[PATCH] arm: Support gcc older than 10 for find_zero_all

[PATCH] arm: Support gcc older than 10 for find_zero_all

[Adhemerval Zanella]

__builtin_arm_uqsub8 is only available on gcc newer or equal than 10.

Checked on arm-linux-gnueabihf built with gcc 9.
---
 sysdeps/arm/armv6t2/string-fza.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sysdeps/arm/armv6t2/string-fza.h b/sysdeps/arm/armv6t2/string-fza.h
index 76274ccca7..d85ce86434 100644
--- a/sysdeps/arm/armv6t2/string-fza.h
+++ b/sysdeps/arm/armv6t2/string-fza.h
@@ -33,7 +33,13 @@ find_zero_all (op_t x)
   /* Use unsigned saturated subtraction from 1 in each byte.
      That leaves 1 for every byte that was zero.  */
   op_t ones = repeat_bytes (0x01);
+#if __GNUC_PREREQ (10, 0)
   return __builtin_arm_uqsub8 (ones, x);
+#else
+  op_t ret;
+  asm ("uqsub8 %0,%1,%2" : "=r"(ret) : "r"(ones), "r"(x));
+  return ret;
+#endif
 }
 
 /* Identify bytes that are equal between X1 and X2.  */
-- 
2.34.1

Re: [PATCH] arm: Support gcc older than 10 for find_zero_all

[Richard Henderson]

On 2/20/23 06:48, Adhemerval Zanella via Libc-alpha wrote:
> __builtin_arm_uqsub8 is only available on gcc newer or equal than 10.
> 
> Checked on arm-linux-gnueabihf built with gcc 9.
> ---
>   sysdeps/arm/armv6t2/string-fza.h | 6 ++++++
>   1 file changed, 6 insertions(+)

Whoops, thanks.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

> 
> diff --git a/sysdeps/arm/armv6t2/string-fza.h b/sysdeps/arm/armv6t2/string-fza.h
> index 76274ccca7..d85ce86434 100644
> --- a/sysdeps/arm/armv6t2/string-fza.h
> +++ b/sysdeps/arm/armv6t2/string-fza.h
> @@ -33,7 +33,13 @@ find_zero_all (op_t x)
>     /* Use unsigned saturated subtraction from 1 in each byte.
>        That leaves 1 for every byte that was zero.  */
>     op_t ones = repeat_bytes (0x01);
> +#if __GNUC_PREREQ (10, 0)
>     return __builtin_arm_uqsub8 (ones, x);
> +#else
> +  op_t ret;
> +  asm ("uqsub8 %0,%1,%2" : "=r"(ret) : "r"(ones), "r"(x));
> +  return ret;
> +#endif
>   }
>   
>   /* Identify bytes that are equal between X1 and X2.  */

Re: [PATCH] arm: Support gcc older than 10 for find_zero_all

[Wilco Dijkstra]

Hi Adhemerval,

> __builtin_arm_uqsub8 is only available on gcc newer or equal than 10.

> +#if __GNUC_PREREQ (10, 0)
>   return __builtin_arm_uqsub8 (ones, x);
> +#else
> +  op_t ret;
> +  asm ("uqsub8 %0,%1,%2" : "=r"(ret) : "r"(ones), "r"(x));
> +  return ret;
> +#endif

__builtin_arm_uqsub8 is an internal builtin function which might change -
the correct way is to include "arm_acle.h" and use __uqsub8 (). Since LLVM
doesn't seem to support this, it may be easier to only keep the inline assembler
for now.

Cheers,
Wilco