[PATCH 18/59] math: Suppress clang -Wabsolute-value warning on math_check_force_underflow

[Sam James]

Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

> clang warns:
>
>   ../sysdeps/x86/fpu/powl_helper.c:233:3: error: absolute value function
>   '__builtin_fabsf' given an argument of type 'typeof (res)' (aka 'long
>   double') but has parameter of type 'float' which may cause truncation of
>   value [-Werror,-Wabsolute-value]
>     math_check_force_underflow (res);
>     ^
>   ./math-underflow.h:45:11: note: expanded from macro
>   'math_check_force_underflow'
>         if (fabs_tg (force_underflow_tmp)                         \
>             ^
>   ./math-underflow.h:27:20: note: expanded from macro 'fabs_tg'
>   #define fabs_tg(x) __MATH_TG ((x), (__typeof (x)) __builtin_fabs, (x))
>                      ^
>   ../math/math.h:899:16: note: expanded from macro '__MATH_TG'
>                  float: FUNC ## f ARGS,           \
>                         ^
>   <scratch space>:73:1: note: expanded from here
>   __builtin_fabsf
>   ^

Reviewed-by: Sam James <sam@gentoo.org>

>
> Due the use of _Generic from TG_MATH.
> ---
>  math/math-underflow.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/math/math-underflow.h b/math/math-underflow.h
> index faac88098b..049d5f5bca 100644
> --- a/math/math-underflow.h
> +++ b/math/math-underflow.h
> @@ -23,6 +23,7 @@
>  #include <math.h>
>  
>  #include <math-barriers.h>
> +#include <libc-diag.h>
>  
>  #define fabs_tg(x) __MATH_TG ((x), (__typeof (x)) __builtin_fabs, (x))
>  
> @@ -37,10 +38,17 @@
>  #define min_of_type(x) __MATH_TG ((x), (__typeof (x)) min_of_type_, ())
>  
>  /* If X (which is not a NaN) is subnormal, force an underflow
> -   exception.  */
> +   exception.
> +
> +   clang issues a warning where _Generic is using a non expected
> +   builtin which may cause truncation of value.
> +
> +   clang warns the value might trunced due the use of _Generics. */

might be truncated

>  #define math_check_force_underflow(x)				\
>    do								\
>      {								\
> +      DIAG_PUSH_NEEDS_COMMENT_CLANG;				\
> +      DIAG_IGNORE_NEEDS_COMMENT_CLANG (18, "-Wabsolute-value"); \
>        __typeof (x) force_underflow_tmp = (x);			\
>        if (fabs_tg (force_underflow_tmp)				\
>  	  < min_of_type (force_underflow_tmp))			\
> @@ -49,6 +57,7 @@
>  	    = force_underflow_tmp * force_underflow_tmp;	\
>  	  math_force_eval (force_underflow_tmp2);		\
>  	}							\
> +      DIAG_POP_NEEDS_COMMENT_CLANG;				\
>      }								\
>    while (0)
>  /* Likewise, but X is also known to be nonnegative.  */