[Bug c/60759] New: -Wlogical-op should perhaps warn about two-way implicit conversions

[giuliano.procida at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60759

            Bug ID: 60759
           Summary: -Wlogical-op should perhaps warn about two-way
                    implicit conversions
           Product: gcc
           Version: 4.6.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: giuliano.procida at googlemail dot com

Expressions of the form "a && b" or "a || b" that involve both implicit
bool->integer and implicit integer->bool coercion, represent a probable misuse
of a logical operator.

These should perhaps generate warnings, particularly for C++ code:

int foo(int x);

int a = foo(1) || foo(2);  // Confusion with Perl, Python behaviour,
int one = 2 && 3;          // or perhaps bitwise operation was intended.

These should not probably generate warnings:

while (foo(1) || foo(2));
int zero = (1 != 2) && (3 == 4);

Example:

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 

$ cat foo.c
static int x = 2 || 3;
int main() { return x; }

$ gcc -Wall -Wextra -Wlogical-op foo.c
$ g++ -Wall -Wextra -Wlogical-op foo.c
[no warnings]