rustc_passes/liveness/
rwu_table.rsuse std::iter;
use crate::liveness::{LiveNode, Variable};
#[derive(Clone, Copy)]
pub(super) struct RWU {
pub(super) reader: bool,
pub(super) writer: bool,
pub(super) used: bool,
}
pub(super) struct RWUTable {
live_nodes: usize,
vars: usize,
words: Vec<u8>,
live_node_words: usize,
}
impl RWUTable {
const RWU_READER: u8 = 0b0001;
const RWU_WRITER: u8 = 0b0010;
const RWU_USED: u8 = 0b0100;
const RWU_MASK: u8 = 0b1111;
const RWU_BITS: usize = 4;
const WORD_BITS: usize = std::mem::size_of::<u8>() * 8;
const WORD_RWU_COUNT: usize = Self::WORD_BITS / Self::RWU_BITS;
pub(super) fn new(live_nodes: usize, vars: usize) -> RWUTable {
let live_node_words = (vars + Self::WORD_RWU_COUNT - 1) / Self::WORD_RWU_COUNT;
Self { live_nodes, vars, live_node_words, words: vec![0u8; live_node_words * live_nodes] }
}
fn word_and_shift(&self, ln: LiveNode, var: Variable) -> (usize, u32) {
assert!(ln.index() < self.live_nodes);
assert!(var.index() < self.vars);
let var = var.index();
let word = var / Self::WORD_RWU_COUNT;
let shift = Self::RWU_BITS * (var % Self::WORD_RWU_COUNT);
(ln.index() * self.live_node_words + word, shift as u32)
}
fn pick2_rows_mut(&mut self, a: LiveNode, b: LiveNode) -> (&mut [u8], &mut [u8]) {
assert!(a.index() < self.live_nodes);
assert!(b.index() < self.live_nodes);
assert!(a != b);
let a_start = a.index() * self.live_node_words;
let b_start = b.index() * self.live_node_words;
unsafe {
let ptr = self.words.as_mut_ptr();
(
std::slice::from_raw_parts_mut(ptr.add(a_start), self.live_node_words),
std::slice::from_raw_parts_mut(ptr.add(b_start), self.live_node_words),
)
}
}
pub(super) fn copy(&mut self, dst: LiveNode, src: LiveNode) {
if dst == src {
return;
}
let (dst_row, src_row) = self.pick2_rows_mut(dst, src);
dst_row.copy_from_slice(src_row);
}
pub(super) fn union(&mut self, dst: LiveNode, src: LiveNode) -> bool {
if dst == src {
return false;
}
let mut changed = false;
let (dst_row, src_row) = self.pick2_rows_mut(dst, src);
for (dst_word, src_word) in iter::zip(dst_row, &*src_row) {
let old = *dst_word;
let new = *dst_word | src_word;
*dst_word = new;
changed |= old != new;
}
changed
}
pub(super) fn get_reader(&self, ln: LiveNode, var: Variable) -> bool {
let (word, shift) = self.word_and_shift(ln, var);
(self.words[word] >> shift) & Self::RWU_READER != 0
}
pub(super) fn get_writer(&self, ln: LiveNode, var: Variable) -> bool {
let (word, shift) = self.word_and_shift(ln, var);
(self.words[word] >> shift) & Self::RWU_WRITER != 0
}
pub(super) fn get_used(&self, ln: LiveNode, var: Variable) -> bool {
let (word, shift) = self.word_and_shift(ln, var);
(self.words[word] >> shift) & Self::RWU_USED != 0
}
pub(super) fn get(&self, ln: LiveNode, var: Variable) -> RWU {
let (word, shift) = self.word_and_shift(ln, var);
let rwu_packed = self.words[word] >> shift;
RWU {
reader: rwu_packed & Self::RWU_READER != 0,
writer: rwu_packed & Self::RWU_WRITER != 0,
used: rwu_packed & Self::RWU_USED != 0,
}
}
pub(super) fn set(&mut self, ln: LiveNode, var: Variable, rwu: RWU) {
let mut packed = 0;
if rwu.reader {
packed |= Self::RWU_READER;
}
if rwu.writer {
packed |= Self::RWU_WRITER;
}
if rwu.used {
packed |= Self::RWU_USED;
}
let (word, shift) = self.word_and_shift(ln, var);
let word = &mut self.words[word];
*word = (*word & !(Self::RWU_MASK << shift)) | (packed << shift)
}
}