RFC: Use std::{min,max} instead of MIN/MAX?

RFC: Use std::{min,max} instead of MIN/MAX?

[Marek Polacek]

Uros had the idea of using std::min/max instead of our MIN/MAX
macros defined in system.h.  I thought I would do this cleanup,
but very soon I ran into a problem of failed template argument
substitution: std::min/max function templates require that both
arguments be of the same type:

/home/marek/src/gcc/gcc/caller-save.c: In function ‘void replace_reg_with_saved_mem(rtx_def**, machine_mode, int, void*)’:
/home/marek/src/gcc/gcc/caller-save.c:1151:63: error: no matching function for call to ‘min(int, short unsigned int)’
      offset -= (std::min (UNITS_PER_WORD, GET_MODE_SIZE (mode))
                                                               ^
In file included from /usr/include/c++/5.1.1/bits/char_traits.h:39:0,
                 from /usr/include/c++/5.1.1/string:40,
                 from /home/marek/src/gcc/gcc/system.h:201,
                 from /home/marek/src/gcc/gcc/caller-save.c:21:
/usr/include/c++/5.1.1/bits/stl_algobase.h:195:5: note: candidate: template<class _Tp> const _Tp& std::min(const _Tp&, const _Tp&)
     min(const _Tp& __a, const _Tp& __b)
     ^
/usr/include/c++/5.1.1/bits/stl_algobase.h:195:5: note:   template argument deduction/substitution failed:
/home/marek/src/gcc/gcc/caller-save.c:1151:63: note:   deduced conflicting types for parameter ‘const _Tp’ (‘int’ and ‘short unsigned int’)
      offset -= (std::min (UNITS_PER_WORD, GET_MODE_SIZE (mode))

We can work around this by using casts, but that seems too ugly a solution.
So it appears to me that we're stuck with our MIN/MAX macros.

Thoughts?

	Marek

Re: RFC: Use std::{min,max} instead of MIN/MAX?

[Trevor Saunders]

On Fri, Jul 10, 2015 at 03:19:10PM +0200, Marek Polacek wrote:
> Uros had the idea of using std::min/max instead of our MIN/MAX
> macros defined in system.h.  I thought I would do this cleanup,
> but very soon I ran into a problem of failed template argument
> substitution: std::min/max function templates require that both
> arguments be of the same type:
> 
> /home/marek/src/gcc/gcc/caller-save.c: In function ‘void replace_reg_with_saved_mem(rtx_def**, machine_mode, int, void*)’:
> /home/marek/src/gcc/gcc/caller-save.c:1151:63: error: no matching function for call to ‘min(int, short unsigned int)’
>       offset -= (std::min (UNITS_PER_WORD, GET_MODE_SIZE (mode))
>                                                                ^
> In file included from /usr/include/c++/5.1.1/bits/char_traits.h:39:0,
>                  from /usr/include/c++/5.1.1/string:40,
>                  from /home/marek/src/gcc/gcc/system.h:201,
>                  from /home/marek/src/gcc/gcc/caller-save.c:21:
> /usr/include/c++/5.1.1/bits/stl_algobase.h:195:5: note: candidate: template<class _Tp> const _Tp& std::min(const _Tp&, const _Tp&)
>      min(const _Tp& __a, const _Tp& __b)
>      ^
> /usr/include/c++/5.1.1/bits/stl_algobase.h:195:5: note:   template argument deduction/substitution failed:
> /home/marek/src/gcc/gcc/caller-save.c:1151:63: note:   deduced conflicting types for parameter ‘const _Tp’ (‘int’ and ‘short unsigned int’)
>       offset -= (std::min (UNITS_PER_WORD, GET_MODE_SIZE (mode))
> 
> We can work around this by using casts, but that seems too ugly a solution.

You can also explicitly pick the specialization you want with e.g.
std::max<long long> (x, y); its kind of long, but I can see an argument
for the explicitness so I'm not sure how ugly I think it is.

Trev


> So it appears to me that we're stuck with our MIN/MAX macros.
> 
> Thoughts?
> 
> 	Marek

Re: RFC: Use std::{min,max} instead of MIN/MAX?

[Marek Polacek]

On Fri, Jul 10, 2015 at 03:35:57PM -0400, Trevor Saunders wrote:
> You can also explicitly pick the specialization you want with e.g.
> std::max<long long> (x, y); its kind of long, but I can see an argument
> for the explicitness so I'm not sure how ugly I think it is.

Thanks for pointing this out.  Yea, that'd be an option, though I don't
think people would be too happy about that.

	Marek