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Auto merge of #96838 - tmiasko:lazy-switch-sources, r=oli-obk

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Optimize switch sources representation and usage

* Avoid constructing switch sources unless necessary - switch sources are used by backward analysis with a custom switch int edge effects, but are otherwise unnecessarily computed.
* Use sparse representation of switch sources to avoid quadratic space overhead.
This commit is contained in:
bors 2022-05-09 22:15:30 +00:00
commit cb390735b0
3 changed files with 11 additions and 10 deletions
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2
compiler/rustc_middle/src/mir/mod.rs
View File

@ -580,6 +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.
#[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);
}
}

7
compiler/rustc_mir_dataflow/src/framework/direction.rs
View File

@ -269,9 +269,9 @@ impl Direction for Backward {
mir::TerminatorKind::SwitchInt { targets: _, ref discr, switch_ty: _ } => {
let mut applier = BackwardSwitchIntEdgeEffectsApplier {
body,
pred,
exit_state,
values: &body.switch_sources()[bb][pred],
bb,
propagate: &mut propagate,
effects_applied: false,
@ -305,9 +305,9 @@ impl Direction for Backward {
}
struct BackwardSwitchIntEdgeEffectsApplier<'a, D, F> {
body: &'a mir::Body<'a>,
pred: BasicBlock,
exit_state: &'a mut D,
values: &'a [Option<u128>],
bb: BasicBlock,
propagate: &'a mut F,
@ -322,7 +322,8 @@ where
fn apply(&mut self, mut apply_edge_effect: impl FnMut(&mut D, SwitchIntTarget)) {
assert!(!self.effects_applied);
let targets = self.values.iter().map(|&value| SwitchIntTarget { value, target: self.bb });
let values = &self.body.switch_sources()[&(self.bb, self.pred)];
let targets = values.iter().map(|&value| SwitchIntTarget { value, target: self.bb });
let mut tmp = None;
for target in targets {