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From: "jzwinck at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/107298] New: Failure to compile code with
 std::optional and ASan/UBSan
Date: Mon, 17 Oct 2022 15:01:54 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: sanitizer
X-Bugzilla-Version: 12.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107298

            Bug ID: 107298
           Summary: Failure to compile code with std::optional and
                    ASan/UBSan
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jzwinck at gmail dot com
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxi=
n at gcc dot gnu.org
  Target Milestone: ---

Test case which is expected to compile:

    #include <optional>

    std::optional<bool> f(bool cond)
    {
        if (cond) {
            return std::make_optional(true);
        }
        return {};
    }

    bool g()
    {
        return *f(true);
    }

GCC 10, 11 and 12 all fail to compile this with "-Wall -Wextra -Werror -O2
-fsanitize=3Dundefined":

    error: '*(unsigned char*)((char*)&<unnamed> +
offsetof(std::optional<bool>,std::optional<bool>::<unnamed>.std::_Optional_=
base<bool,
true, true>::<unnamed>))' may be used uninitialized
[-Werror=3Dmaybe-uninitialized]
        return {};

Removing std::make_optional or replacing it with std::optional<bool> makes =
the
error go away, though these changes should be irrelevant since they're not =
on
the code path the compiler complains about.  Compiling without a sanitizer =
also
works fine.

Demo: https://godbolt.org/z/TafE9cxWW=