[Bug c++/98625] UBSAN: gcc/cp/module.cc:977:15: runtime error: left shift of negative value -1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98625

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

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

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Note, -1 << x shifts are well defined in C++20 (assuming x < sizeof (int) *
CHAR_BIT), but isn't well defined in older C++ versions.  For C++11 .. C++17
in particular, x << y is UB if x < 0 or ((unsigned) x >> (sizeof (int) *
CHAR_BIT - 1 - y)) > 1 (in addition to the usual y < 0 or y >= sizeof (int) *
CHAR_BIT).