https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92054
Bug ID: 92054
Summary: `final` does not cause devirtualization of nested
calls
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Consider the example:
struct A {
virtual int f() { return 0; }
virtual int g() { return f() + 40; }
};
struct B2 final : A {
int f() override { return 42; }
};
int test(B2& b) {
return b.g();
}
GCC-10 generates the assembly that does a fair vptr call. However, `B2` is
final, so any call to the virtual functions of `A` end up with a call to the
same function in `B2`. So `B2::g()` should inline the `A::g()` and get
optimized to:
int test(B2& b) { return B2::f() + 40; }
Which is just 82, because `B2::f()` always returns 42.
Godbolt playground: https://godbolt.org/z/PJ4nL-
