C++ PATCH for __has_cpp_attribute and fallthrough

Jason Merrill jason@redhat.com
Mon Sep 26 15:58:00 GMT 2016


OK.

On Mon, Sep 26, 2016 at 8:23 AM, Marek Polacek <polacek@redhat.com> wrote:
> This patch updates __has_cpp_attribute for fallthrough, which is now supported.
>
> The system.h hunk should aid people building trunk GCC with older GCC 7 not
> supporting this attribute yet.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2016-09-26  Marek Polacek  <polacek@redhat.com>
>
>         * c-lex.c (c_common_has_attribute): Handle attribute fallthrough.
>
>         * system.h: Use __has_attribute to check whether the fallthrough
>         attribute is supported.
>
>         * g++.dg/cpp1z/feat-cxx1z.C: Test attribute fallthrough.
>
> diff --git gcc/c-family/c-lex.c gcc/c-family/c-lex.c
> index 829c18b..5c6496e 100644
> --- gcc/c-family/c-lex.c
> +++ gcc/c-family/c-lex.c
> @@ -350,7 +350,8 @@ c_common_has_attribute (cpp_reader *pfile)
>               else if (is_attribute_p ("deprecated", attr_name))
>                 result = 201309;
>               else if (is_attribute_p ("maybe_unused", attr_name)
> -                      || is_attribute_p ("nodiscard", attr_name))
> +                      || is_attribute_p ("nodiscard", attr_name)
> +                      || is_attribute_p ("fallthrough", attr_name))
>                 result = 201603;
>               if (result)
>                 attr_name = NULL_TREE;
> diff --git gcc/system.h gcc/system.h
> index 8ca71cf..0952e4f 100644
> --- gcc/system.h
> +++ gcc/system.h
> @@ -746,8 +746,12 @@ extern void fancy_abort (const char *, int, const char *) ATTRIBUTE_NORETURN;
>  #define gcc_unreachable() (fancy_abort (__FILE__, __LINE__, __FUNCTION__))
>  #endif
>
> -#if GCC_VERSION >= 7000
> -# define gcc_fallthrough() __attribute__((fallthrough))
> +#if GCC_VERSION >= 7000 && defined(__has_attribute)
> +# if __has_attribute(fallthrough)
> +#  define gcc_fallthrough() __attribute__((fallthrough))
> +# else
> +#  define gcc_fallthrough()
> +# endif
>  #else
>  # define gcc_fallthrough()
>  #endif
> diff --git gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C
> index 982572e..71c8c7d 100644
> --- gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C
> +++ gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C
> @@ -370,6 +370,12 @@
>  #    error "__has_cpp_attribute(nodiscard) != 201603"
>  #  endif
>
> +#  if ! __has_cpp_attribute(fallthrough)
> +#    error "__has_cpp_attribute(fallthrough)"
> +#  elif __has_cpp_attribute(fallthrough) != 201603
> +#    error "__has_cpp_attribute(fallthrough) != 201603"
> +#  endif
> +
>  #else
>  #  error "__has_cpp_attribute"
>  #endif
>
>         Marek



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