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Use a SmallVec for Cache::predecessors. #70876

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Merged
merged 1 commit into from
Apr 8, 2020
Merged

Use a SmallVec for Cache::predecessors. #70876

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16 changes: 11 additions & 5 deletions src/librustc_middle/mir/cache.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,13 +5,15 @@ use rustc_data_structures::graph::{self, GraphPredecessors, GraphSuccessors};
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_index::vec::IndexVec;
use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
use smallvec::SmallVec;
use std::iter;
use std::ops::{Deref, DerefMut, Index, IndexMut};
use std::vec::IntoIter;

#[derive(Clone, Debug)]
pub struct Cache {
predecessors: Option<IndexVec<BasicBlock, Vec<BasicBlock>>>,
// Typically 95%+ of the inner vectors have 4 or fewer elements.
predecessors: Option<IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>>>,
}

impl rustc_serialize::Encodable for Cache {
Expand Down Expand Up @@ -44,7 +46,7 @@ impl Cache {

pub fn ensure_predecessors(&mut self, body: &Body<'_>) {
if self.predecessors.is_none() {
let mut result = IndexVec::from_elem(vec![], body.basic_blocks());
let mut result = IndexVec::from_elem(smallvec![], body.basic_blocks());
for (bb, data) in body.basic_blocks().iter_enumerated() {
if let Some(ref term) = data.terminator {
for &tgt in term.successors() {
Expand All @@ -58,7 +60,11 @@ impl Cache {
}

/// This will recompute the predecessors cache if it is not available
fn predecessors(&mut self, body: &Body<'_>) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
// njn: typedef?
fn predecessors(
&mut self,
body: &Body<'_>,
) -> &IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>> {
self.ensure_predecessors(body);
self.predecessors.as_ref().unwrap()
}
Expand Down Expand Up @@ -137,7 +143,7 @@ impl BodyAndCache<'tcx> {
self.cache.ensure_predecessors(&self.body);
}

pub fn predecessors(&mut self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
pub fn predecessors(&mut self) -> &IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>> {
self.cache.predecessors(&self.body)
}

Expand Down Expand Up @@ -199,7 +205,7 @@ impl ReadOnlyBodyAndCache<'a, 'tcx> {
Self { body, cache }
}

pub fn predecessors(&self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
pub fn predecessors(&self) -> &IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>> {
self.cache.predecessors.as_ref().unwrap()
}

Expand Down