Re: [PATCH] Rewrite gdb_mpz::operator==

[Simon Marchi <simark@simark.ca>]

On 4/19/23 11:09, Tom Tromey via Gdb-patches wrote:
> Simon pointed out that the recent changes to gdb_mpz caused a build
> failure on macOS.  It turns out to be somewhat difficult to overload a

For some reason, just macOS on amd64, not arm64.

> method in a way that will work "naturally" for all integer types;
> especially in a case like gdb_mpz::operator==, where it's desirable to
> special case all integer types that are no wider than 'long'.
> 
> After a false start, I came up with this patch, which seems to work.
> It applies the desirable GMP special cases directly in the body,
> rather than via overloads.
> ---
>  gdb/gmp-utils.h | 38 ++++++++++++++------------------------
>  1 file changed, 14 insertions(+), 24 deletions(-)
> 
> diff --git a/gdb/gmp-utils.h b/gdb/gmp-utils.h
> index d05c11ecbe4..3586d01b0f9 100644
> --- a/gdb/gmp-utils.h
> +++ b/gdb/gmp-utils.h
> @@ -323,31 +323,21 @@ struct gdb_mpz
>      return mpz_cmp_si (m_val, other) < 0;
>    }
>  
> -  bool operator== (int other) const
> -  {
> -    return mpz_cmp_si (m_val, other) == 0;
> -  }
> -
> -  bool operator== (long other) const
> -  {
> -    return mpz_cmp_si (m_val, other) == 0;
> -  }
> -
> -  bool operator== (unsigned long other) const
> -  {
> -    return mpz_cmp_ui (m_val, other) == 0;
> -  }
> -
>    template<typename T,
> -	   typename = gdb::Requires<
> -	     gdb::And<std::is_integral<T>,
> -		      std::integral_constant<bool,
> -					     (sizeof (T) > sizeof (long))>>
> -	     >
> -	   >
> -  bool operator== (T src)
> -  {
> -    return *this == gdb_mpz (src);
> +	   typename = gdb::Requires<std::is_integral<T>>>
> +  bool operator== (T other) const
> +  {
> +    if (std::is_signed<T>::value)
> +      {
> +	if (other == (T) (long) other)

It's a bit hard to understand what the intent is, if you don't know the
problematic already.  Could you add a comment explaining that?

Also, wouldn't it work to compare size?  Like:

  if (sizeof (T) <= sizeof (long))

Simon