bjoernager/rust
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Use sparse representation of switch sources

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to avoid quadratic space overhead
This commit is contained in:
Tomasz Miąsko 2022-05-08 00:00:00 +00:00
parent fbc3cc18be
commit 2be012a0c6
3 changed files with 8 additions and 10 deletions
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4
compiler/rustc_middle/src/mir/mod.rs
View file

@ -580,8 +580,8 @@ impl<'tcx> Body<'tcx> {
self.predecessor_cache.compute(&self.basic_blocks)
}
/// `body.switch_sources()[target][switch]` returns a list of switch values
/// that lead to a `target` block from a `switch` block.
/// `body.switch_sources()[&(target, switch)]` returns a list of switch
/// values that lead to a `target` block from a `switch` block.
#[inline]
pub fn switch_sources(&self) -> &SwitchSources {
self.switch_source_cache.compute(&self.basic_blocks)

12
compiler/rustc_middle/src/mir/switch_sources.rs
View file

@ -2,6 +2,7 @@
//! `Predecessors`/`PredecessorCache`.
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_data_structures::stable_map::FxHashMap;
use rustc_data_structures::sync::OnceCell;
use rustc_index::vec::IndexVec;
use rustc_serialize as serialize;
@ -9,7 +10,7 @@ use smallvec::SmallVec;
use crate::mir::{BasicBlock, BasicBlockData, Terminator, TerminatorKind};
pub type SwitchSources = IndexVec<BasicBlock, IndexVec<BasicBlock, SmallVec<[Option<u128>; 1]>>>;
pub type SwitchSources = FxHashMap<(BasicBlock, BasicBlock), SmallVec<[Option<u128>; 1]>>;
#[derive(Clone, Debug)]
pub(super) struct SwitchSourceCache {
@ -35,19 +36,16 @@ impl SwitchSourceCache {
basic_blocks: &IndexVec<BasicBlock, BasicBlockData<'_>>,
) -> &SwitchSources {
self.cache.get_or_init(|| {
let mut switch_sources = IndexVec::from_elem(
IndexVec::from_elem(SmallVec::new(), basic_blocks),
basic_blocks,
);
let mut switch_sources: SwitchSources = FxHashMap::default();
for (bb, data) in basic_blocks.iter_enumerated() {
if let Some(Terminator {
kind: TerminatorKind::SwitchInt { targets, .. }, ..
}) = &data.terminator
{
for (value, target) in targets.iter() {
switch_sources[target][bb].push(Some(value));
switch_sources.entry((target, bb)).or_default().push(Some(value));
}
switch_sources[targets.otherwise()][bb].push(None);
switch_sources.entry((targets.otherwise(), bb)).or_default().push(None);
}
}