* [PATCH] doc: Describe behaviour of enums with fixed underlying type
@ 2023-04-27 11:16 Jonathan Wakely
2023-04-27 15:58 ` Marek Polacek
0 siblings, 1 reply; 3+ messages in thread
From: Jonathan Wakely @ 2023-04-27 11:16 UTC (permalink / raw)
To: gcc-patches
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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] doc: Describe behaviour of enums with fixed underlying type
2023-04-27 11:16 [PATCH] doc: Describe behaviour of enums with fixed underlying type Jonathan Wakely
@ 2023-04-27 15:58 ` Marek Polacek
2023-05-02 20:43 ` Jonathan Wakely
0 siblings, 1 reply; 3+ messages in thread
From: Marek Polacek @ 2023-04-27 15:58 UTC (permalink / raw)
To: Jonathan Wakely; +Cc: gcc-patches
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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] doc: Describe behaviour of enums with fixed underlying type
2023-04-27 15:58 ` Marek Polacek
@ 2023-05-02 20:43 ` Jonathan Wakely
0 siblings, 0 replies; 3+ messages in thread
From: Jonathan Wakely @ 2023-05-02 20:43 UTC (permalink / raw)
To: Marek Polacek; +Cc: gcc-patches
[-- Attachment #1: Type: text/plain, Size: 2320 bytes --]
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
>
>
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2023-04-27 15:58 ` Marek Polacek
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