Re: [PATCH] doc: Describe behaviour of enums with fixed underlying type
On Thu, 27 Apr 2023 at 16:58, Marek Polacek wrote: > 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. > That's an ack C front end reviewer (thanks!), do I need an ack from a C++/docs/global review too, or can I push? > > > -- >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 > >
Re: [PATCH] doc: Describe behaviour of enums with fixed underlying type
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
[PATCH] doc: Describe behaviour of enums with fixed underlying type
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