Re: [PATCH] ARC:fpu: add extra capability check before use of sqrt and fma builtins

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

On 21/12/22 13:28, Pavel.Kozlov--- via Libc-alpha wrote:
> From: Pavel Kozlov <pavel.kozlov@synopsys.com>
> 
> Add extra check for compiler definitions to ensure that compiler provides
> sqrt and fma hw fpu instructions else use software implementation.
> 
> As divide/sqrt and FMA hw support from CPU side is optional,
> the compiler can be configured by options to generate hw FPU instructions,
> but without use of FDDIV, FDSQRT, FSDIV, FSSQRT, FDMADD and FSMADD
> instructions. In this case __builtin_sqrt and __builtin_sqrtf provided by
> compiler can't be used inside the glibc code, as these builtins are used
> in implementations of sqrt() and sqrtf() functions but at the same time
> these builtins unfold to sqrt() and sqrtf(). So it is possible to receive
> code like that:
> 
> 0001c4b4 <__ieee754_sqrtf>:
>    1c4b4:    0001 0000      b     0         ;1c4b4 <__ieee754_sqrtf>
> 
> The same is also true for __builtin_fma and __builtin_fmaf.
> ---
>  sysdeps/arc/fpu/math-use-builtins-fma.h  | 14 ++++++++++++--
>  sysdeps/arc/fpu/math-use-builtins-sqrt.h | 14 ++++++++++++--
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/sysdeps/arc/fpu/math-use-builtins-fma.h b/sysdeps/arc/fpu/math-use-builtins-fma.h
> index eede75aa41be..082badf48201 100644
> --- a/sysdeps/arc/fpu/math-use-builtins-fma.h
> +++ b/sysdeps/arc/fpu/math-use-builtins-fma.h
> @@ -1,4 +1,14 @@
> -#define USE_FMA_BUILTIN 1
> -#define USE_FMAF_BUILTIN 1
> +#if defined __ARC_FPU_DP_DIV__
> +# define USE_SQRT_BUILTIN 1
> +#else
> +# define USE_SQRT_BUILTIN 0
> +#endif
> +
> +#if defined __ARC_FPU_SP_DIV__
> +# define USE_SQRTF_BUILTIN 1
> +#else
> +# define USE_SQRTF_BUILTIN 0
> +#endif
> +
>  #define USE_FMAL_BUILTIN 0
>  #define USE_FMAF128_BUILTIN 0

This is wrong, sqrt use macro do not belong for the fma switch file.

> diff --git a/sysdeps/arc/fpu/math-use-builtins-sqrt.h b/sysdeps/arc/fpu/math-use-builtins-sqrt.h
> index e94c915ba66a..a449bc609295 100644
> --- a/sysdeps/arc/fpu/math-use-builtins-sqrt.h
> +++ b/sysdeps/arc/fpu/math-use-builtins-sqrt.h
> @@ -1,4 +1,14 @@
> -#define USE_SQRT_BUILTIN 1
> -#define USE_SQRTF_BUILTIN 1
> +#if defined __ARC_FPU_DP_DIV__
> +# define USE_SQRT_BUILTIN 1
> +#else
> +# define USE_SQRT_BUILTIN 0
> +#endif
> +
> +#if defined __ARC_FPU_SP_DIV__
> +# define USE_SQRTF_BUILTIN 1
> +#else
> +# define USE_SQRTF_BUILTIN 0
> +#endif
> +
>  #define USE_SQRTL_BUILTIN 0
>  #define USE_SQRTF128_BUILTIN 0

This is ok.