https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115410
Bug ID: 115410
Summary: Missing optimization: typeid(*a)==typeid(*b) could be
optimized to a->_vptr==b->_vptr
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: user202729 at protonmail dot com
Target Milestone: ---
As in the title. I think if both `*a` and `*b` are objects of type with a
virtual pointer then `typeid(*a)==typeid(*b)` could be optimized to
if(!a) throw bad_typeid;
if(!b) throw bad_typeid;
return a->_vptr==b->_vptr;
Godbolt: https://godbolt.org/z/MjY67Pc4b
Although I think this optimization should be done at the level of the C++ front
end (`cp_build_binary_op`?) because once the expression is down to gimple level
then it becomes something like
type_info::operator==(a->_vptr[-1], b->vptr[-1])
and it seems not clean to hard code the constant `-1` (it is currently hard
coded only in `get_tinfo_decl_dynamic` function).
