debug extension overhead

[Silvius Rus]

(This is only about the debug extension.)


Hello libstdc++ maintainers,

Have you considered adding a knob that would turn on a subset of
_GLIBCXX_DEBUG checks that have lower overhead, e.g., guaranteed
constant factor?  Some users are giving up on it due to high overhead
in certain cases, but they could benefit from cheap checks, such as
vector subscript checks.  Also, it would increase its usability in
time sensitive applications.

1. Does this make sense?  Would this hurt in any way other than adding
maintenance overhead?

2. How hard would it be to implement something like _GLIBCXX_DEBUG_FAST?


Thank you,
Silvius