http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50495
Bug #: 50495 Summary: Optimize exact matches in overload resolution Classification: Unclassified Product: gcc Version: unknown Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: math...@gaunard.com Overload resolution in GCC (and in C++ in general) is quite slow, and I would like to suggest the following enhancement: look-up (in constant or logarithmic time) for exact matches first, then perform regular overload resolution if necessary. The idea is that struct id_0 {}; void f(id_0); struct id_1; void f(id_1) {}; ... and then calling f(id_x()); should be as fast as void f_0(); void f_1(); ... and then calling f_x(); Now if this could be made to work for things like struct h0 {}; struct h1 : h0 {}; struct id_0 {}; template<class T> void f(id_0, h0<T>); template<class T> void f(id_0, h1<T>); to reduce the set of possible overloads to 2 early (templates inserted to make it non-absolutely orderable), that would be perfect. According to my benchmarks, resolving a function with an exact match on the first argument among 1,000 tags with 10 overloads each takes 30s, while with 1,000 differently named functions of 10 overloads each it takes 100ms.