rucc-target 0.11.19

//! Finding an entry of a target's tables by its name.
//!
//! Every question a pass asks a target about an opcode is asked by name, and the tables that
//! answer are lists of names in the order the description was written in. Looking a name up by
//! walking the list compares it against every name before it, which for x86-64's seven hundred
//! opcodes is a few hundred string comparisons, and a pass asks that for every instruction of
//! every function. On jtckdint that walk was about a seventh of the whole `-O2` build.
//!
//! So each table is hashed once, the first time anybody asks it anything, and every question after
//! that is one hash of the name.

use std::collections::HashMap;

/// Where each name in that table is.
///
/// A name that is in the table twice is found where it is first, which is what walking the table
/// would have found.
pub(crate) fn index<T>(table: &[(&'static str, T)]) -> HashMap<&'static str, usize> {
    let mut at = HashMap::with_capacity(table.len());
    for (number, &(name, _)) in table.iter().enumerate() {
        at.entry(name).or_insert(number);
    }
    at
}

/// Every place each name is in that table, in the order they come in, for a table where one name
/// has several rows and the caller picks between them.
pub(crate) fn every<T>(
    table: &[T],
    name: impl Fn(&T) -> &'static str,
) -> HashMap<&'static str, Vec<usize>> {
    let mut at: HashMap<&'static str, Vec<usize>> = HashMap::new();
    for (number, entry) in table.iter().enumerate() {
        at.entry(name(entry)).or_default().push(number);
    }
    at
}