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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/98625] UBSAN: gcc/cp/module.cc:977:15: runtime error: left
 shift of negative value -1
Date: Thu, 21 Jan 2021 08:58:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98625

Martin Li=C5=A1ka <marxin at gcc dot gnu.org> changed:

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

--- Comment #5 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
Fixed with:

commit 911f797a9be2dc8ef59f5d5bd6d68baf650b8822
Author: Nathan Sidwell <nathan@acm.org>
Date:   Wed Jan 20 09:21:02 2021 -0800

    c++: Avoid UB in signed shift [PR 98625]

    I'd forgotten that left shifting a negative value is UB until C++20.
    Insert some casts to do unsigned shifts.

            PT c++/98625
            gcc/cp/
            * module.cc (bytes_in::i, bytes_in::wi): Avoid left shift of
            signed type.

@Nathan: That was very close, s/PT/PR :)=