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? -- >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
