[Bug c/59293] New: Bogus -Wsign-compare warning when using typeof() on a constant

[Bug c/59293] New: Bogus -Wsign-compare warning when using typeof() on a constant

[shawn at churchofgit dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59293

            Bug ID: 59293
           Summary: Bogus -Wsign-compare warning when using typeof() on a
                    constant
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shawn at churchofgit dot com

#define MAX(a,b)                                 \
        __extension__ ({                         \
                        typeof(a) _a = (a);      \
                        typeof(b) _b = (b);      \
                        _a > _b ? _a : _b;       \
                })

int main() {
    if (MAX(5, (unsigned)3))
        return 1;
    return 0;
}


gives:
excessive_signed_compare.c:5:28: warning: comparison between signed and
unsigned integer expressions [-Wsign-compare]
                         _a > _b ? _a : _b;       \
                            ^
excessive_signed_compare.c:9:6: note: in expansion of macro ‘MAX’
  if (MAX(5, (unsigned)3))
      ^
excessive_signed_compare.c:5:38: warning: signed and unsigned type in
conditional expression [-Wsign-compare]
                         _a > _b ? _a : _b;       \
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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/59258] ubsan: ICE(segfault): stack-buffer-overflow with -fsanitize=undefined
Date: Mon, 25 Nov 2013 20:10:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY258

--- Comment #11 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #10)
> Created attachment 31289 [details]
> Untested fix for the dwarf2out.c ICE.

Seem to solve the problem with both -g and no "-g" for one unreduced test file.
Thanks!

> Perhaps my
>         * ubsan.c (ubsan_source_location): Don't crash on unknown locations.
> change will be unneeded now?

Possibly yes; when I revert it, PR59250's test case still passes and also the
unreduced test case (for this PR's problem) passes. (I will try the bigger code
tomorrow.)

[Bug c/59293] Bogus -Wsign-compare warning when using typeof() on a constant

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59293

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I don't think this is a bogus warning as the warning is correct as you have a
signed int variable > unsigned int variable.  The compiler does not know that
variable is assigned to a constant here.