https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103826
Bug ID: 103826 Summary: Bogus shift-negative-value warning in C++20 mode Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: manx-bugzilla at problemloesungsmaschine dot de Target Milestone: --- C++20 changed the semantics when shifting negative values from undefined behavior to defined semantics. However, GCC still warns with -std=c++20 in this case, which is unfortunate, because it generates a lot of warnings when porting code to modern C++20. The warning is enabled by -Wextra. ``` int foo() { return (-32767) << 3; } ``` `-std=c++20 -Wall -Wextra -Wpedantic`: ``` <source>: In function 'int foo()': <source>:2:21: warning: left shift of negative value [-Wshift-negative-value] 2 | return (-32767) << 3; | ~~~~~~~~~^~~~ ``` Clang also warns in this case in C++17 mode, but does not warn in C++20 mode. See <https://godbolt.org/z/8Yd9qfveP>.