RE: [PATCH 1/2] eal: add unreachable and precondition hints

["Morten Brørup" <mb@smartsharesystems.com>]

Ping for review.

> From: Morten Brørup [mailto:mb@smartsharesystems.com]
> Sent: Friday, 25 October 2024 13.52
> 
> Added two new compiler/optimizer hints:
> * The __rte_unreachable hint for use in points in code known never to
> be
> reached.
> * The __rte_assume hint for providing information about preconditions
> the
> compiler/optimizer might be unable to figure out by itself.
> 
> Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> ---
>  lib/eal/include/rte_common.h | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/lib/eal/include/rte_common.h
> b/lib/eal/include/rte_common.h
> index c79f9ed319..2f143c87e4 100644
> --- a/lib/eal/include/rte_common.h
> +++ b/lib/eal/include/rte_common.h
> @@ -366,6 +366,16 @@ static void
> __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
>  #define __rte_noreturn __attribute__((noreturn))
>  #endif
> 
> +/**
> + * Hint point in program never reached
> + */
> +#if defined(RTE_TOOLCHAIN_GCC) || defined(RTE_TOOLCHAIN_CLANG)
> +#define __rte_unreachable() __extension__(__builtin_unreachable())
> +#else
> +/* MSVC or ICC */
> +#define __rte_unreachable() __assume(0)
> +#endif
> +
>  /**
>   * Issue a warning in case the function's return value is ignored.
>   *
> @@ -423,6 +433,23 @@ static void
> __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
>  #define __rte_cold __attribute__((cold))
>  #endif
> 
> +/**
> + * Hint precondition
> + *
> + * @warning Depending on the compiler, any code in ``condition`` might
> be executed.
> + * This currently only occurs with GCC prior to version 13.
> + */
> +#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 130000)
> +#define __rte_assume(condition) __attribute__((assume(condition)))
> +#elif defined(RTE_TOOLCHAIN_GCC)
> +#define __rte_assume(condition) do { if (!(condition))
> __rte_unreachable(); } while (0)
> +#elif defined(RTE_TOOLCHAIN_CLANG)
> +#define __rte_assume(condition)
> __extension__(__builtin_assume(condition))
> +#else
> +/* MSVC or ICC */
> +#define __rte_assume(condition) __assume(condition)
> +#endif
> +
>  /**
>   * Disable AddressSanitizer on some code
>   */
> --
> 2.43.0