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[WIP] MIR move elimination pass #156046

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a8e96df
Remove incorrect comments about Rvalue::Aggregate not being allowed
Amanieu Apr 24, 2026
2fc24d4
Pass block to `visit_block_start` and `visit_block_end`
Amanieu Apr 28, 2026
8af1fb3
Various changes to `SparseIntervalMatrix`
Amanieu May 2, 2026
62e9181
WIP move elimination
Amanieu May 2, 2026
490bdec
Relax MIR lint to allow use of a maybe-dead local
Amanieu May 21, 2026
df40d2f
Speed up handling of block end in precise_liveness
Amanieu May 28, 2026
c1a4988
Don't use kill points for locals that are ever borrowed
Amanieu May 30, 2026
c837d9c
Add tests for move elimination
Amanieu May 30, 2026
0c83904
Add a MIR pass which turns copies into moves just before a return
Amanieu May 31, 2026
86bb416
Avoid merging into the tuples that are passed to "rust-call"
Amanieu Jun 1, 2026
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63 changes: 52 additions & 11 deletions compiler/rustc_index/src/interval.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
use std::iter::Step;
use std::marker::PhantomData;
use std::ops::{Bound, Range, RangeBounds};
use std::ops::{Bound, RangeBounds};
use std::range::RangeInclusive;

use smallvec::SmallVec;

Expand Down Expand Up @@ -59,11 +60,14 @@ impl<I: Idx> IntervalSet<I> {
}

/// Iterates through intervals stored in the set, in order.
pub fn iter_intervals(&self) -> impl Iterator<Item = std::ops::Range<I>>
pub fn iter_intervals(&self) -> impl Iterator<Item = RangeInclusive<I>>
where
I: Step,
{
self.map.iter().map(|&(start, end)| I::new(start as usize)..I::new(end as usize + 1))
self.map.iter().map(|&(start, end)| RangeInclusive {
start: I::new(start as usize),
last: I::new(end as usize),
})
}

/// Returns true if we increased the number of elements present.
Expand Down Expand Up @@ -204,17 +208,38 @@ impl<I: Idx> IntervalSet<I> {
needle <= *prev_end
}

/// Returns whether any point in `range` is contained in the set.
pub fn intersects_range(&self, range: impl RangeBounds<I> + Clone) -> bool {
let start = inclusive_start(range.clone());
let Some(end) = inclusive_end(self.domain, range) else {
// empty range
return false;
};
if start > end {
return false;
}

// Find the last interval whose start is <= end.
let Some(last) = self.map.partition_point(|r| r.0 <= end).checked_sub(1) else {
// All ranges in the map start after the new range's end
return false;
};
let (_, prev_end) = &self.map[last];
start <= *prev_end
}

pub fn superset(&self, other: &IntervalSet<I>) -> bool
where
I: Step,
{
let mut sup_iter = self.iter_intervals();
let mut current = None;
let contains = |sup: Range<I>, sub: Range<I>, current: &mut Option<Range<I>>| {
if sup.end < sub.start {
// if `sup.end == sub.start`, the next sup doesn't contain `sub.start`
let contains = |sup: RangeInclusive<I>,
sub: RangeInclusive<I>,
current: &mut Option<RangeInclusive<I>>| {
if sup.last < sub.start {
None // continue to the next sup
} else if sup.end >= sub.end && sup.start <= sub.start {
} else if sup.last >= sub.last && sup.start <= sub.start {
*current = Some(sup); // save the current sup
Some(true)
} else {
Expand All @@ -224,8 +249,8 @@ impl<I: Idx> IntervalSet<I> {
other.iter_intervals().all(|sub| {
current
.take()
.and_then(|sup| contains(sup, sub.clone(), &mut current))
.or_else(|| sup_iter.find_map(|sup| contains(sup, sub.clone(), &mut current)))
.and_then(|sup| contains(sup, sub, &mut current))
.or_else(|| sup_iter.find_map(|sup| contains(sup, sub, &mut current)))
.unwrap_or(false)
})
}
Expand All @@ -242,11 +267,11 @@ impl<I: Idx> IntervalSet<I> {
let mut other_current = other_iter.next()?;

loop {
if self_current.end <= other_current.start {
if self_current.last < other_current.start {
self_current = self_iter.next()?;
continue;
}
if other_current.end <= self_current.start {
if other_current.last < self_current.start {
other_current = other_iter.next()?;
continue;
}
Expand Down Expand Up @@ -370,6 +395,12 @@ impl<R: Idx, C: Step + Idx> SparseIntervalMatrix<R, C> {
self.rows.get(row)
}

pub fn clear_row(&mut self, row: R) {
if let Some(row) = self.rows.get_mut(row) {
row.clear();
}
}

fn ensure_row(&mut self, row: R) -> &mut IntervalSet<C> {
self.rows.ensure_contains_elem(row, || IntervalSet::new(self.column_size))
}
Expand All @@ -393,6 +424,16 @@ impl<R: Idx, C: Step + Idx> SparseIntervalMatrix<R, C> {
write_row.union(read_row)
}

pub fn disjoint_rows(&self, a: R, b: R) -> bool
where
C: Step,
{
let (Some(a), Some(b)) = (self.rows.get(a), self.rows.get(b)) else {
return true;
};
a.disjoint(b)
}

pub fn insert_all_into_row(&mut self, row: R) {
self.ensure_row(row).insert_all();
}
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_index/src/interval/tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ fn insert_collapses() {
let mut set = IntervalSet::<u32>::new(10000);
set.insert_range(9831..=9837);
set.insert_range(43..=9830);
assert_eq!(set.iter_intervals().collect::<Vec<_>>(), [43..9838]);
assert_eq!(set.iter_intervals().collect::<Vec<_>>(), [(43..=9837).into()]);
}

#[test]
Expand Down
4 changes: 0 additions & 4 deletions compiler/rustc_middle/src/mir/syntax.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -124,7 +124,6 @@ pub enum RuntimePhase {
/// disallowed:
/// * [`TerminatorKind::Yield`]
/// * [`TerminatorKind::CoroutineDrop`]
/// * [`Rvalue::Aggregate`] for any `AggregateKind` except `Array`
/// * [`Rvalue::CopyForDeref`]
/// * [`PlaceElem::OpaqueCast`]
/// * [`LocalInfo::DerefTemp`](super::LocalInfo::DerefTemp)
Expand Down Expand Up @@ -1442,9 +1441,6 @@ pub enum Rvalue<'tcx> {
/// This is needed because dataflow analysis needs to distinguish
/// `dest = Foo { x: ..., y: ... }` from `dest.x = ...; dest.y = ...;` in the case that `Foo`
/// has a destructor.
///
/// Disallowed after deaggregation for all aggregate kinds except `Array` and `Coroutine`. After
/// coroutine lowering, `Coroutine` aggregate kinds are disallowed too.
Aggregate(Box<AggregateKind<'tcx>>, IndexVec<FieldIdx, Operand<'tcx>>),

/// A CopyForDeref is equivalent to a read from a place at the
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_mir_dataflow/src/framework/direction.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -212,7 +212,7 @@ impl Direction for Backward {
) where
A: Analysis<'tcx>,
{
vis.visit_block_end(state);
vis.visit_block_end(state, block);

let loc = Location { block, statement_index: block_data.statements.len() };
let term = block_data.terminator();
Expand All @@ -229,7 +229,7 @@ impl Direction for Backward {
vis.visit_after_primary_statement_effect(analysis, state, stmt, loc);
}

vis.visit_block_start(state);
vis.visit_block_start(state, block);
}
}

Expand Down Expand Up @@ -391,7 +391,7 @@ impl Direction for Forward {
) where
A: Analysis<'tcx>,
{
vis.visit_block_start(state);
vis.visit_block_start(state, block);

for (statement_index, stmt) in block_data.statements.iter().enumerate() {
let loc = Location { block, statement_index };
Expand All @@ -408,6 +408,6 @@ impl Direction for Forward {
analysis.apply_primary_terminator_effect(state, term, loc);
vis.visit_after_primary_terminator_effect(analysis, state, term, loc);

vis.visit_block_end(state);
vis.visit_block_end(state, block);
}
}
4 changes: 2 additions & 2 deletions compiler/rustc_mir_dataflow/src/framework/graphviz.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -660,13 +660,13 @@ where
A: Analysis<'tcx>,
A::Domain: DebugWithContext<A>,
{
fn visit_block_start(&mut self, state: &A::Domain) {
fn visit_block_start(&mut self, state: &A::Domain, _block: BasicBlock) {
if A::Direction::IS_FORWARD {
self.prev_state.clone_from(state);
}
}

fn visit_block_end(&mut self, state: &A::Domain) {
fn visit_block_end(&mut self, state: &A::Domain, _block: BasicBlock) {
if A::Direction::IS_BACKWARD {
self.prev_state.clone_from(state);
}
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_mir_dataflow/src/framework/visitor.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@ pub trait ResultsVisitor<'tcx, A>
where
A: Analysis<'tcx>,
{
fn visit_block_start(&mut self, _state: &A::Domain) {}
fn visit_block_start(&mut self, _state: &A::Domain, _block: BasicBlock) {}

/// Called after the "early" effect of the given statement is applied to `state`.
fn visit_after_early_statement_effect(
Expand Down Expand Up @@ -90,5 +90,5 @@ where
) {
}

fn visit_block_end(&mut self, _state: &A::Domain) {}
fn visit_block_end(&mut self, _state: &A::Domain, _block: BasicBlock) {}
}
4 changes: 4 additions & 0 deletions compiler/rustc_mir_dataflow/src/impls/mod.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
mod borrowed_locals;
mod initialized;
mod liveness;
mod precise_liveness;
mod storage_liveness;

pub use self::borrowed_locals::{MaybeBorrowedLocals, borrowed_locals};
Expand All @@ -12,6 +13,9 @@ pub use self::liveness::{
DefUse, MaybeLiveLocals, MaybeTransitiveLiveLocals,
TransferFunction as LivenessTransferFunction,
};
pub use self::precise_liveness::{
SplitPointEffect, SplitPointIndex, dump_liveness_matrix, liveness_matrix,
};
pub use self::storage_liveness::{
MaybeRequiresStorage, MaybeStorageDead, MaybeStorageLive, always_storage_live_locals,
};
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