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SubjectRe: [PATCH -tip v3 09/11] data_race: Avoid nested statement expression
On Tue, May 26, 2020 at 07:33:12PM +0200, Marco Elver wrote:
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 5faf68eae204..a529fa263906 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -245,7 +245,9 @@ struct ftrace_likely_data {
> /*
> * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving
> * non-scalar types unchanged.
> - *
> + */
> +#if defined(CONFIG_CC_IS_GCC) && CONFIG_GCC_VERSION < 40900
> +/*
> * We build this out of a couple of helper macros in a vain attempt to
> * help you keep your lunch down while reading it.
> */
> @@ -267,6 +269,24 @@ struct ftrace_likely_data {
> __pick_integer_type(x, int, \
> __pick_integer_type(x, long, \
> __pick_integer_type(x, long long, x))))))
> +#else
> +/*
> + * If supported, prefer C11 _Generic for better compile-times. As above, 'char'
> + * is not type-compatible with 'signed char', and we define a separate case.
> + */
> +#define __scalar_type_to_expr_cases(type) \
> + type: (type)0, unsigned type: (unsigned type)0
> +
> +#define __unqual_scalar_typeof(x) typeof( \
> + _Generic((x), \
> + __scalar_type_to_expr_cases(char), \
> + signed char: (signed char)0, \
> + __scalar_type_to_expr_cases(short), \
> + __scalar_type_to_expr_cases(int), \
> + __scalar_type_to_expr_cases(long), \
> + __scalar_type_to_expr_cases(long long), \
> + default: (x)))
> +#endif
>
> /* Is this type a native word size -- useful for atomic operations */
> #define __native_word(t) \
>

Yeah, this shaves around 5% off of my kernel builds. The _Atomic hack is
every so slightly faster on GCC but apparently doesn't work on clang --
also, it's disguisting :-)

Ack!

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