Re: [PATCH 3/5] gdb: allow duplicate enumerators in flag enums

[Tom Tromey <tom@tromey.com>]

>>>>> "Simon" == Simon Marchi <simon.marchi@efficios.com> writes:

Simon> I have come across some uses cases where it would be desirable to treat
Simon> an enum that has duplicate values as a "flag enum".  For example, this
Simon> one here [1]:

Simon>             /* Alias for header backward compatibility. */
Simon>             MEMBARRIER_CMD_SHARED = MEMBARRIER_CMD_GLOBAL,
Simon>     };

Simon> The last enumerator is kept for backwards compatibility.  Without this
Simon> patch, this enumeration wouldn't be considered a flag enum, because two
Simon> enumerators collide.   With this patch, it would be considered a flag
Simon> enum, and the value 3 would be printed as:

Does it always choose the first enumerator?

Simon>  	  if (nbits != 0 && nbits && nbits != 1)
Simon>  	    flag_enum = 0;
Simon> -	  else if ((mask & value) != 0)
Simon> -	    flag_enum = 0;
Simon> -	  else
Simon> -	    mask |= value;

I wonder if this allows too much, though.

Maybe instead it should check for duplicate enumerator values and allow
those, while still disallowing enums with conflicts, like:

enum x {
  one = 0x11,
  two = 0x10,
  three = 0x01
};

... which probably isn't a sensible flag enum.

Tom