[Bug c++/105164] New: new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[Bug c++/105164] New: new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

            Bug ID: 105164
           Summary: new warning in clang, missing in gcc:
                    -Wbitwise-instead-of-logical
           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:

extern bool f1( int);
extern void f3( int);

void
f2( int n)
{
        if (!f1(n) & !f1( n + 1))
                f3( n - 1);

        if (!f1(n) | !f1( n + 1))
                f3( n + 1);
}

recent gcc trunk says not a lot:

$ /home/dcb/gcc/results/bin/g++ -g -O2 -Wall -Wextra -pedantic -c jul01a.cc
$

However, new clang-14 says:

$ clang++ -g -O2 -Wall -Wextra -pedantic -c jul01a.cc
jul01a.cc:8:6: warning: use of bitwise '&' with boolean operands
[-Wbitwise-instead-of-logical]
        if (!f1(n) & !f1( n + 1))
            ^~~~~~~~~~~~~~~~~~~~
                   &&
jul01a.cc:8:6: note: cast one or both operands to int to silence this warning
jul01a.cc:11:6: warning: use of bitwise '|' with boolean operands
[-Wbitwise-instead-of-logical]
        if (!f1(n) | !f1( n + 1))
            ^~~~~~~~~~~~~~~~~~~~
                   ||
jul01a.cc:11:6: note: cast one or both operands to int to silence this warning
2 warnings generated.
$ 

Static analyser cppcheck also finds the problem:

$ /home/dcb/cppcheck/trunk.git/cppcheck --enable=all jul01a.cc
jul01a.cc:8:13: style: Boolean result is used in bitwise operation. Clarify
expression with parentheses. [clarifyCondition]
 if (!f1(n) & !f1( n + 1))
            ^
jul01a.cc:11:13: style: Boolean result is used in bitwise operation. Clarify
expression with parentheses. [clarifyCondition]
 if (!f1(n) | !f1( n + 1))
            ^
jul01a.cc:6:0: style: The function 'f2' is never used. [unusedFunction]

^

[Bug c++/105164] new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

--- Comment #1 from David Binderman <dcb314 at hotmail dot com> ---
Interestingly, I tried a build of gcc trunk with the new clang-14
and got many cases of this warning.

$ grep "warning:.*Wbitwise-instead-of-logical" mk.out | sort | uniq -c > /tmp/0
$ wc -l /tmp/0
16 /tmp/0
$ cat /tmp/0
      1 :184:13: warning: use of bitwise '&' with boolean operands
[-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/c-family/c-attribs.cc:2384:9: warning: use of
bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/cp/decl.cc:11850:7: warning: use of bitwise '&'
with boolean operands [-Wbitwise-instead-of-logical]
      2 ../../trunk.git/gcc/cp/lex.cc:124:24: warning: use of bitwise '&' with
boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/cp/lex.cc:571:11: warning: use of bitwise '&' with
boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/cp/module.cc:16843:11: warning: use of bitwise '&'
with boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/cp/name-lookup.cc:7528:12: warning: use of bitwise
'&' with boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/cp/parser.cc:883:11: warning: use of bitwise '&'
with boolean operands [-Wbitwise-instead-of-logical]
     51 ../../trunk.git/gcc/function-abi.h:177:13: warning: use of bitwise '&'
with boolean operands [-Wbitwise-instead-of-logical]
     49 ../../trunk.git/gcc/function-abi.h:184:13: warning: use of bitwise '&'
with boolean operands [-Wbitwise-instead-of-logical]
      1
../../trunk.git/gcc/function-abi.h../../trunk.git/gcc/loop-unroll.cc::1841750::1319::
 warning: warning: use of bitwise '&' with boolean operands
[-Wbitwise-instead-of-logical]array index 1 is past the end of the array (which
contains 1 element) [-Warray-bounds]
      1 ../../trunk.git/gcc/gimple-ssa-sprintf.cc:1225:19: warning: use of
bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/gimple-ssa-sprintf.cc:1664:12: warning: use of
bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
      1 ../../trunk.git/gcc/rtl.h:../../trunk.git/gcc/function-abi.h:184:13:
warning: use of bitwise '&' with boolean operands
[-Wbitwise-instead-of-logical]
      1 :../../trunk.git/gcc/rtl.h warning: :use of bitwise '&' with boolean
operands [-Wbitwise-instead-of-logical]1237
      5 ../../trunk.git/gcc/rtl-ssa/internals.inl:436:25: warning: use of
bitwise '&' with boolean operands [-Wbitwise-instead-of-logical]

On the evidence of the source code of gcc, this new clang warning
might be worth implementing in gcc.

[Bug c++/105164] new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

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

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

[Bug c++/105164] new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |marxin at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2022-04-06
     Ever confirmed|0                           |1

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
I'm going to fix the warnings in GCC compiler.

[Bug c++/105164] new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|marxin at gcc dot gnu.org          |unassigned at gcc dot gnu.org
             Status|ASSIGNED                    |NEW

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Well, I doubt the warning is much useful.

There are situations where we can't use short-circuit evaluation:

gcc/c-family/c-attribs.cc:2384:
  else if (TREE_CODE (decl) == FUNCTION_DECL
           && (((curalign = DECL_ALIGN (decl)) > bitalign)
               | ((lastalign = DECL_ALIGN (last_decl)) > bitalign)))

or we want to quickly and flags of a struct:

  gcc_checking_assert (!IDENTIFIER_KIND_BIT_2 (id)
                       & !IDENTIFIER_KIND_BIT_1 (id)
                       & !IDENTIFIER_KIND_BIT_0 (id));

Note a different code is generated for situations like:

return foo() && bar() && baz ();

and

return foo() & bar() & baz ();

So I don't think we should change the code based on the warnings.

[Bug c++/105164] new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

--- Comment #4 from David Binderman <dcb314 at hotmail dot com> ---
I had a quick look at the two warnings for gcc/gimple-ssa-sprintf.cc
and they look like they could move from | to || happily.

[Bug c++/105164] new warning in clang, missing in gcc: -Wbitwise-instead-of-logical

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105164

--- Comment #5 from David Binderman <dcb314 at hotmail dot com> ---
Same for trunk.git/gcc/rtl-ssa/internals.inl. The result is going into a bool,
so I see no need for |, only ||.