On Thu, Apr 27, 2023 at 12:16:34PM +0100, Jonathan Wakely via Gcc-patches wrote:
> C2x adds the ability to give an enumeration type a fixed underlying
> type, as C++ already has. The -fshort-enums option alters the compiler's
> choice of underlying type, but when it's fixed the compiler can't
> choose.
>
> Similarly for C++ -fstrict-enums has no effect with a fixed underlying
> type, because every value of the underlying type is a valid value of the
> enumeration type.
>
> This caused confusion recently: https://gcc.gnu.org/PR109532
>
> OK for trunk?
LGTM.
> -- >8 --
>
> gcc/ChangeLog:
>
> * doc/invoke.texi (Code Gen Options): Note that -fshort-enums
> is ignored for a fixed underlying type.
> (C++ Dialect Options): Likewise for -fstrict-enums.
> ---
> gcc/doc/invoke.texi | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 2f40c58b21c..0f91464f8c0 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -3495,6 +3495,8 @@ defined in the C++ standard; basically, a value that
> can be
> represented in the minimum number of bits needed to represent all the
> enumerators). This assumption may not be valid if the program uses a
> cast to convert an arbitrary integer value to the enumerated type.
> +This option has no effect for an enumeration type with a fixed underlying
> +type.
>
> @opindex fstrong-eval-order
> @item -fstrong-eval-order
> @@ -18303,6 +18305,8 @@ Use it to conform to a non-default application binary
> interface.
> Allocate to an @code{enum} type only as many bytes as it needs for the
> declared range of possible values. Specifically, the @code{enum} type
> is equivalent to the smallest integer type that has enough room.
> +This option has no effect for an enumeration type with a fixed underlying
> +type.
>
> @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
> code that is not binary compatible with code generated without that switch.
> --
> 2.40.0
>
Marek
