syntax_data: {"ast_node_type":"function","tokens":[{"end":43,"kind":"keyword","start":0,"text":"pub"}]}
source_snippet:     pub fn reg_index(self) -> Option<u32> {
context_before:     /// If the register is an integer register then return its index.
context_after:         // Unlike `vreg_index`, we can't subtract `x0` to get the u32 because