Generics can not reliably be optimized. They create specialized inline code by monomorphization (except partially in Go which is a bit smarter). Specialization and inlining can be good if it leads to simplificatons or bad when it leads to a combinatorial explosion, which is why optimizers are careful with it to avoid code bloat. Generics always create the bloat by default. If this were a good strategy, optimizers would always inline.
To reliable devirtualize function pointers in C you need to use non-standard extensions. But the best strategy is not let the optimizer decide and apply this very carefully inly for the few selected cases where it matters.