[Bug c/65120] New: [gcc5] Wlogical-not-parentheses should not wanr about double exclamation !!

[Bug c/65120] New: [gcc5] Wlogical-not-parentheses should not wanr about double exclamation !!

[jirislaby at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

            Bug ID: 65120
           Summary: [gcc5] Wlogical-not-parentheses should not wanr about
                    double exclamation !!
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jirislaby at gmail dot com

While warning about
  "if (!a == b)"
is perfectly fine and I like it, I do not like warning about
  "if (!!a = b)"
at all. It generates plenty of false positives (in the Linux kernel at least)
and I doubt it can warn about an error at all.

Better than papering over this as
  "if ((!aa) = b)"
or by -Wno-logical-not-parentheses does not make much sense to me (opposing to
the single ! case).

Note: this is all about:
"logical not is only applied to the left hand side of comparison"

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-19
      Known to work|                            |4.9.2
   Target Milestone|---                         |5.0
            Summary|[gcc5]                      |[5 Regression]
                   |Wlogical-not-parentheses    |Wlogical-not-parentheses
                   |should not warn about       |should not warn about
                   |double exclamation !!       |double exclamation !!
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
testcase you can compile and which warns with -Wall

int a, b;
int main()
{
  if (!!a == b)
    return 1;
  return 0;
}

[Bug c/65120] [gcc5] Wlogical-not-parentheses should not warn about double exclamation !!

[jirislaby at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #1 from Jiri Slaby <jirislaby at gmail dot com> ---
(In reply to Jiri Slaby from comment #0)
> Better than papering over this as
>   "if ((!aa) = b)"

Pardon me, it should write:
  "if ((!!aa) = b)"

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
And yes, the required

  if ((!!a) == b)

is totally fugly.

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Oh, you can also workaround with

  if (b == !!a)

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

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

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Looks reasonable, I'll take a look.

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

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

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

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 34811
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34811&action=edit
gcc5-pr65120.patch

Untested fix.

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

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

--- Comment #7 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Causes c-c++-common/pr62199-2.c failures:

+FAIL: c-c++-common/pr62199-2.c  -Wc++-compat   (test for warnings, line 14)
+FAIL: c-c++-common/pr62199-2.c  -Wc++-compat   (test for warnings, line 15)
+FAIL: c-c++-common/pr62199-2.c  -Wc++-compat   (test for warnings, line 16)
+FAIL: c-c++-common/pr62199-2.c  -Wc++-compat   (test for warnings, line 17)
+FAIL: c-c++-common/pr62199-2.c  -Wc++-compat   (test for warnings, line 18)
+FAIL: c-c++-common/pr62199-2.c  -Wc++-compat   (test for warnings, line 19)

+FAIL: c-c++-common/pr62199-2.c  -std=gnu++11  (test for warnings, line 14)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++11  (test for warnings, line 15)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++11  (test for warnings, line 16)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++11  (test for warnings, line 17)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++11  (test for warnings, line 18)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++11  (test for warnings, line 19)

+FAIL: c-c++-common/pr62199-2.c  -std=gnu++14  (test for warnings, line 14)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++14  (test for warnings, line 15)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++14  (test for warnings, line 16)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++14  (test for warnings, line 17)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++14  (test for warnings, line 18)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++14  (test for warnings, line 19)


+FAIL: c-c++-common/pr62199-2.c  -std=gnu++98  (test for warnings, line 14)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++98  (test for warnings, line 15)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++98  (test for warnings, line 16)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++98  (test for warnings, line 17)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++98  (test for warnings, line 18)
+FAIL: c-c++-common/pr62199-2.c  -std=gnu++98  (test for warnings, line 19)

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #8 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The pr62199-2.c test is tweaked in the posted version of the patch:
https://gcc.gnu.org/ml/gcc-patches/2015-02/msg01237.html

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, just saw

> [ 2808s] ../drivers/xen/sfc_netfront/falcon_event.c:113:43: error: logical
> not is only applied to the left hand side of comparison 
> [-Werror=logical-not-parentheses]
> [ 2808s]   BUG_ON(!QWORD_GET_U(RX_EV_BYTE_CNT, *ev) == 0);
> [ 2808s]                                            ^

which I think we should preserve - so make sure that the !! special-casing
doesn't cover this case from macro expansion.

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
It was just noted that

"But then again (!a == 0) is the same as !(a == 0), so the warning
is pretty pointless when the right side is constant zero."

so we should probably not warn for this case either.

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Mon Mar  9 18:26:52 2015
New Revision: 221284

URL: https://gcc.gnu.org/viewcvs?rev=221284&root=gcc&view=rev
Log:
    PR c/65120
    * c-typeck.c (parser_build_binary_op): Don't warn for
    !!x == y or !b == y where b is _Bool.

    * parser.c (cp_parser_binary_expression): Don't warn for
    !!x == y or !b == y where b is bool.

    * c-c++-common/pr49706.c: Adjust tests for not warning
    about !!x == y or !b == y where b is boolean, and add
    some further tests.
    * c-c++-common/pr62199-2.c: Likewise.

Modified:
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-typeck.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/parser.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/c-c++-common/pr49706.c
    trunk/gcc/testsuite/c-c++-common/pr62199-2.c

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Tue Mar 10 06:38:57 2015
New Revision: 221299

URL: https://gcc.gnu.org/viewcvs?rev=221299&root=gcc&view=rev
Log:
    PR c/65120
    * c-common.c (warn_logical_not_parentheses): Don't warn for
    !x == 0 or !x != 0.

    * c-typeck.c (parser_build_binary_op): Check for tcc_comparison
    before preparing arguments to warn_logical_not_parentheses.

    * parser.c (cp_parser_binary_expression): Check for tcc_comparison
    before preparing arguments to warn_logical_not_parentheses.
    Use maybe_constant_value on rhs.

    * c-c++-common/pr49706.c (fn2): Don't expect warning if enumerator
    on rhs is 0.
    (fn4): New test.
    * c-c++-common/pr65120.c: New test.

Added:
    trunk/gcc/testsuite/c-c++-common/pr65120.c
Modified:
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c-common.c
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-typeck.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/parser.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/c-c++-common/pr49706.c

[Bug c/65120] [5 Regression] Wlogical-not-parentheses should not warn about double exclamation !!

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65120

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.