[libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Bernardo Innocenti]

Hello,

this patch adds the ARG_UNUSED() macro to be used in place of
ATTRIBUTE_UNUSED.  The syntax looks like this:

	void foo (ARG_UNUSED (int, x))
	{
	} 

The C++ frontend can't parse attribute((unused)) when it
appears after the variable name.  The cleanest work-around
is using the standard C++ syntax to specify unused
parameters, which can also be used when bootstrapping from
other C++ compilers.

This patch is a prerequisite for the upcoming C++ bootstrap
patches that I've been preparing.


include/
2004-07-11  Bernardo Innocenti  <bernie@develer.com>

	* ansidecl.h (ARG_UNUSED): New Macro.

diff -u -p -r1.16 ansidecl.h
--- ansidecl.h	17 Jun 2003 14:10:00 -0000	1.16
+++ ansidecl.h	11 Jul 2004 15:38:23 -0000
@@ -312,4 +312,10 @@ So instead we use the macro below and te
 #define __extension__
 #endif
 
+#ifdef __cplusplus
+# define ARG_UNUSED(T, N)	T
+#else
+# define ARG_UNUSED(T, N)	T N ATTRIBUTE_UNUSED
+#endif
+
 #endif	/* ansidecl.h	*/

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Andrew Pinski]

> 
> Hello,
> 
> this patch adds the ARG_UNUSED() macro to be used in place of
> ATTRIBUTE_UNUSED.  The syntax looks like this:
> 
> 	void foo (ARG_UNUSED (int, x))
> 	{
> 	} 
> 
> The C++ frontend can't parse attribute((unused)) when it
> appears after the variable name.  The cleanest work-around
> is using the standard C++ syntax to specify unused
> parameters, which can also be used when bootstrapping from
> other C++ compilers.
> 
> This patch is a prerequisite for the upcoming C++ bootstrap
> patches that I've been preparing.

Huh? Yes it can from 3.4.0 and above.

Thanks,
Andrew Pinski
who is just going through emails from the last two days


> 
> 
> include/
> 2004-07-11  Bernardo Innocenti  <bernie@develer.com>
> 
> 	* ansidecl.h (ARG_UNUSED): New Macro.
> 
> diff -u -p -r1.16 ansidecl.h
> --- ansidecl.h	17 Jun 2003 14:10:00 -0000	1.16
> +++ ansidecl.h	11 Jul 2004 15:38:23 -0000
> @@ -312,4 +312,10 @@ So instead we use the macro below and te
>  #define __extension__
>  #endif
>  
> +#ifdef __cplusplus
> +# define ARG_UNUSED(T, N)	T
> +#else
> +# define ARG_UNUSED(T, N)	T N ATTRIBUTE_UNUSED
> +#endif
> +
>  #endif	/* ansidecl.h	*/
> 
> -- 
>   // Bernardo Innocenti - Develer S.r.l., R&D dept.
> \X/  http://www.develer.com/
> 
> 
> 

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Andrew Cagney]

Just FYI, GDB doesn't use ATTRIB_UNUSED (but thanks for resolving C++ 
problems with these macros).

Andrew

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[DJ Delorie]

This implementation doesn't address K&R style argument lists, although
that's soon to be a moot point ;-)

I'd also prefer this definition to be right after the ATTRIBUTE_UNUSED
definition, rather than randomly added to the end of the file.

However, I'm not convinced we need this yet.  By the time we require a
C++ compiler, 3.4.0 will be old enough to require that version.

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Bernardo Innocenti]

Andrew Pinski wrote:

>>this patch adds the ARG_UNUSED() macro to be used in place of
>>ATTRIBUTE_UNUSED.  The syntax looks like this:
>>
>>	void foo (ARG_UNUSED (int, x))
>>	{
>>	} 
>>
>>The C++ frontend can't parse attribute((unused)) when it
>>appears after the variable name.  The cleanest work-around
>>is using the standard C++ syntax to specify unused
>>parameters, which can also be used when bootstrapping from
>>other C++ compilers.
>>
>>This patch is a prerequisite for the upcoming C++ bootstrap
>>patches that I've been preparing.
> 
> 
> Huh? Yes it can from 3.4.0 and above.

Nevertheless, bootstrap from earlier versions of GCC
would fail (I was using Apple's version of GCC 3.3).

ansidecl.h enables ATTRIBUTE_UNUSED for any GCC > 2.7.
We could make the check stricter, like this:

 #if !defined(__cplusplus) || GCC_VERSION >= 3004
 #define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
 #endif


But I'd much prefer the ARG_UNUSED solution, which can
be made to work with and C or C++ compiler, using whatever
funny syntax the compiler requires.

This macro is in libiberty, which is about portability
across different OSes and compilers.

I also like the ARG_UNUSED syntax because it's somewhat
shorter to type.  (btw, Doxygen can parse it if you
define ARG_UNUSED(T,N) to "T N").

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Bernardo Innocenti]

DJ Delorie wrote:
> This implementation doesn't address K&R style argument lists, although
> that's soon to be a moot point ;-)

Anyway, I think there's no way to get something like this to work:

   foo (a, b, dummy)
     char *a;
     int b;
     ARG_UNUSED (int, dummy);
   {
   }


> I'd also prefer this definition to be right after the ATTRIBUTE_UNUSED
> definition, rather than randomly added to the end of the file.

OK.


> However, I'm not convinced we need this yet.  By the time we require a
> C++ compiler, 3.4.0 will be old enough to require that version.

So we won't be able to bootstrap from third-party C++ compilers?
The ATTRIBUTE_UNUSED macro cannot be made to work with MSVC, CW
or other popular compilers.

Not that I care that much: on any supported host you can always
install an older version of GCC or cross-compile from another host.

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Richard Henderson]

On Tue, Jul 13, 2004 at 09:50:36AM +0200, Bernardo Innocenti wrote:
> define ARG_UNUSED(T,N) to "T N").

If we do this, I'd prefer

	T ARG_UNUSED(N)

#ifdef __cplusplus
# define ARG_UNUSED(N)
#elif somegccversion
# define ARG_UNUSED(N)	N ATTRIBUTE_UNUSED
#else
# define ARG_UNUSED(N)	N
#endif


r~

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Bernardo Innocenti]

Richard Henderson wrote:
> On Tue, Jul 13, 2004 at 09:50:36AM +0200, Bernardo Innocenti wrote:
> 
>>define ARG_UNUSED(T,N) to "T N").
> 
> 
> If we do this, I'd prefer
> 
> 	T ARG_UNUSED(N)
> 
> #ifdef __cplusplus
> # define ARG_UNUSED(N)
> #elif somegccversion
> # define ARG_UNUSED(N)	N ATTRIBUTE_UNUSED
> #else
> # define ARG_UNUSED(N)	N
> #endif

This wouldn't allow us to support g++ < 3.4:

 # define ARG_UNUSED(T,N)   ATTRIBUTE_UNUSED T N

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Richard Henderson]

On Tue, Jul 13, 2004 at 10:15:47AM +0200, Bernardo Innocenti wrote:
> This wouldn't allow us to support g++ < 3.4:
> 
>  # define ARG_UNUSED(T,N)   ATTRIBUTE_UNUSED T N

Well, frankly, I don't care.  We don't build with -Werror 
at stage1 for a reason.


r~

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Jason Merrill]

On Tue, 13 Jul 2004 10:15:47 +0200, Bernardo Innocenti <bernie@develer.com> wrote:

> Richard Henderson wrote:
>> On Tue, Jul 13, 2004 at 09:50:36AM +0200, Bernardo Innocenti wrote:
>> 
>>>define ARG_UNUSED(T,N) to "T N").
>> 
>> 
>> If we do this, I'd prefer
>> 
>> 	T ARG_UNUSED(N)
>> 
>> #ifdef __cplusplus
>> # define ARG_UNUSED(N)
>> #elif somegccversion
>> # define ARG_UNUSED(N)	N ATTRIBUTE_UNUSED
>> #else
>> # define ARG_UNUSED(N)	N
>> #endif
>
> This wouldn't allow us to support g++ < 3.4:
>
>  # define ARG_UNUSED(T,N)   ATTRIBUTE_UNUSED T N

Huh?  rth's definition above supports all C++ compilers just fine.

Jason

Re: [libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Bernardo Innocenti]

Bernd Schmidt wrote:
> On Tue, 13 Jul 2004, Richard Henderson wrote:
>>On Tue, Jul 13, 2004 at 09:50:36AM +0200, Bernardo Innocenti wrote:
>>
>>#ifdef __cplusplus
>># define ARG_UNUSED(N)
>>#elif somegccversion
>># define ARG_UNUSED(N)	N ATTRIBUTE_UNUSED
>>#else
>># define ARG_UNUSED(N)	N
>>#endif
> 
> That fails in cases where the argument is unused only on some targets
> and needed by others.

For those (few) cases, I've handled it by moving ATTRIBUTE_UNUSED
before the typename, which seems to work G++ 3.3 too.


> What's wrong with just disabling ATTRIBUTE_UNUSED for compilers that
> can't handle it?

 - You get lots of annoying warnings in stage1 and when building
   a cross compiler;

 - If we switch to C++, ARG_UNUSED would allow using the standard
   C++ syntax for unused arguments;

 - libiberty.h is used in other projects and it's about portability
   across different compilers and platforms.  The ATTRIBUTE_UNUSED
   macro cannot be made to work usefully with all compilers,
   therefore it must be replaced with something more portable;

 - "int ARG_UNUSED(foo)" is shorter, more readable and sexier than
   "int foo ATTRIBUTE_UNUSED".

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/