[Bug c/105581] New: boolean types and relational operators problem

[Bug c/105581] New: boolean types and relational operators problem

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

            Bug ID: 105581
           Summary: boolean types and relational operators problem
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

For this C code:

void g( int );

void f( bool a, bool b)
{
        if (a < b)
                g( 1);
}

recent gcc doesn't find a problem:

$ /home/dcb/gcc/results/bin/gcc -c -g -O2 -Wall -Wextra -pedantic may12a.cc
$

Here is cppcheck complaining:

$ /home/dcb/cppcheck/trunk.git/cppcheck --enable=all may12a.cc
may12a.cc:6:8: style: Comparison of a variable having boolean value using
relational (<, >, <= or >=) operator. [comparisonOfBoolWithBoolError]
 if (a < b)
       ^
$

There is an example in the gcc source code:

trunk.git/gcc/sreal.h:72:25: style: Comparison of a variable having boolean
value using relational (<, >, <= or >=) operator.
[comparisonOfBoolWithBoolError]

Source code is

        return negative > other_negative;

[Bug c/105581] boolean types and relational operators problem

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Well. There is a meaning for the code though.
That is negative > other_negative
Means negative is true while other_negative is false the result will be true
which is exactly what it is testing here.

[Bug c/105581] boolean types and relational operators problem

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
Equivalent to negative && !other_negative.

[Bug c/105581] boolean types and relational operators problem

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

--- Comment #3 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> Well. There is a meaning for the code though.
> That is negative > other_negative
> Means negative is true while other_negative is false the result will be true
> which is exactly what it is testing here.

In abstract, false and true can't be compared with "<".

In the implementation choice of false as 0 and true as 1, then relying
on the implementation values does make "<" valid.

I think that's the bad style cppcheck is complaining about. It's just
better style to have it as a logical expression, as Andreas shows.

[Bug c/105581] boolean types and relational operators problem

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

--- Comment #4 from Andreas Schwab <schwab@linux-m68k.org> ---
There is nothing abstractly wrong with ordering false and true.

[Bug c/105581] new warning about boolean types and relational operators

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |87403
            Summary|boolean types and           |new warning about boolean
                   |relational operators        |types and relational
                   |problem                     |operators

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is just a style issue really ...


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87403
[Bug 87403] [Meta-bug] Issues that suggest a new warning

[Bug c/105581] new warning about boolean types and relational operators

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105581

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

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