Struct rustc_passes::liveness::RWUTable

struct RWUTable {
    packed_rwus: Vec<u32>,
    unpacked_rwus: Vec<RWU>,
}

Conceptually, this is like a Vec<RWU>. But the number of RWUs can get very large, so it uses a more compact representation that takes advantage of the fact that when the number of RWUs is large, most of them have an invalid reader and an invalid writer.

Fields

packed_rwus: Vec<u32>

Each entry in packed_rwus is either INV_INV_FALSE, INV_INV_TRUE, or an index into unpacked_rwus. In the common cases, this compacts the 65 bits of data into 32; in the uncommon cases, it expands the 65 bits in 96.

More compact representations are possible -- e.g., use only 2 bits per packed RWU and make the secondary table a HashMap that maps from indices to RWUs -- but this one strikes a good balance between size and speed.

unpacked_rwus: Vec<RWU>

Implementations

impl RWUTable

fn new(num_rwus: usize) -> RWUTable

fn get(&self, idx: usize) -> RWU

fn get_reader(&self, idx: usize) -> Option<LiveNode>

fn get_writer(&self, idx: usize) -> Option<LiveNode>

fn get_used(&self, idx: usize) -> bool

fn copy_packed(&mut self, dst_idx: usize, src_idx: usize)

fn assign_unpacked(&mut self, idx: usize, rwu: RWU)

fn assign_inv_inv(&mut self, idx: usize)