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Diffstat (limited to '')
-rw-r--r-- | compiler/rustc_passes/src/liveness/rwu_table.rs | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/compiler/rustc_passes/src/liveness/rwu_table.rs b/compiler/rustc_passes/src/liveness/rwu_table.rs new file mode 100644 index 000000000..6d5983f53 --- /dev/null +++ b/compiler/rustc_passes/src/liveness/rwu_table.rs @@ -0,0 +1,145 @@ +use crate::liveness::{LiveNode, Variable}; +use std::iter; + +#[derive(Clone, Copy)] +pub(super) struct RWU { + pub(super) reader: bool, + pub(super) writer: bool, + pub(super) used: bool, +} + +/// Conceptually, this is like a `Vec<Vec<RWU>>`. But the number of +/// RWU`s can get very large, so it uses a more compact representation. +pub(super) struct RWUTable { + /// Total number of live nodes. + live_nodes: usize, + /// Total number of variables. + vars: usize, + + /// A compressed representation of `RWU`s. + /// + /// Each word represents 2 different `RWU`s packed together. Each packed RWU + /// is stored in 4 bits: a reader bit, a writer bit, a used bit and a + /// padding bit. + /// + /// The data for each live node is contiguous and starts at a word boundary, + /// so there might be an unused space left. + words: Vec<u8>, + /// Number of words per each live node. + 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; + + /// Size of packed RWU in bits. + const RWU_BITS: usize = 4; + /// Size of a word in bits. + const WORD_BITS: usize = std::mem::size_of::<u8>() * 8; + /// Number of packed RWUs that fit into a single word. + 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); + } + + /// Sets `dst` to the union of `dst` and `src`, returns true if `dst` was + /// changed. + 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) + } +} |