https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89824
Bug ID: 89824
Summary: Variant jump table reserves space for __variant_cookie
twice
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Space for the `__variant_cookie` state is already reserved in _Multi_array
`_Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];`.
Additionally reserving it inside the `__gen_vtable` produces jump table with
gaps https://godbolt.org/z/Vx_wEU.
Fix: remove the `+ (is_same_v<_Result_type, __variant_cookie> ? 1 : 0)` from
`__gen_vtable`.
This removes zeros from jump table and slightly reduces the binary size
https://godbolt.org/z/gyo0-j
