[Bug c++/83050] New: Please provide shortcircuit attribute for || and && operators

bugzilla@poradnik-webmastera.com gcc-bugzilla@gcc.gnu.org
Sun Nov 19 14:38:00 GMT 2017


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83050

            Bug ID: 83050
           Summary: Please provide shortcircuit attribute for || and &&
                    operators
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugzilla@poradnik-webmastera.com
  Target Milestone: ---

Built-int || and && operators are shortcircuiting, i.e. they may skip
evaluation of 2nd argument in some cases. However overloaded || and &&
operators do not work in this way, they always evaluate both arguments.
Sometimes it would be handy if they also could support shortcircuiting. I
propose to add new shortcircuit attribute, which could be attached to
overloaded operator:

__attribute__((shortcircuit)) T1 operator||(T2 a, T3 b);
__attribute__((shortcircuit)) T1 operator&&(T2 a, T3 b);

With such attribute gcc would generate a bit different code, e.g. something
like this:

|| operator:
if ((bool)a)
    (T1)a;
else
    operator||(a, b);

&& operator:
if ((bool)a)
    operator&&(a, b);
else
    (T1)a;

This new attribute potentially could also be attached to other overloaded
operators (+, -, ...), but I have doubts if gcc should accept this - probably
it would be better to prohibit this.


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