[Bug c/46509] New: -Wparentheses shouldn't warn about: A || Y && "foo"

[Bug c/46509] New: -Wparentheses shouldn't warn about: A || Y && "foo"

[sabre at nondot dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46509

           Summary: -Wparentheses shouldn't warn about: A || Y && "foo"
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sabre@nondot.org


Per the subject, -Wparentheses shouldn't warn about possible ||/&& precedence
issues if the operand to the or is always false or the operand to && is always
true.  These should not warn:

if (a || b && 1) 
if (0 || a && b) 

They shouldn't warn because even if the user is confused about precedence, the
order of evaluation doesn't affect the result of the computation.

This happens to come up frequently for coding standards that use messages in
asserts, e.g.:

assert(A == 1 || A == 3 && "some reason this property should hold"); 

-Chris

[Bug c/46509] -Wparentheses shouldn't warn about: A || Y && "foo"

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46509

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2010-11-16 22:17:45 UTC ---
>A == 1 || A == 3 && "some reason this property should hold"

To the untrained eye this looks funny really.  The parentheses makes the code
look cleaner and better understood as far as I can tell.

[Bug c/46509] -Wparentheses shouldn't warn about: A || Y && "foo"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46509

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug c/46509] -Wparentheses shouldn't warn about: A || Y && "foo"

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46509

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2010-11-17 12:07:43 UTC ---
Agreed, this is a terrible coding standard, I don't think we should try to
special case it.  It is much better if ()s are added.