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Only clear locals that are known to be written to.

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This commit is contained in:
Camille GILLOT 2023-03-13 17:43:14 +00:00
parent f177b7cb91
commit 0e866af1f7
2 changed files with 53 additions and 16 deletions
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41
compiler/rustc_mir_transform/src/const_prop.rs
View File

@ -4,6 +4,7 @@
use either::Right;
use rustc_const_eval::const_eval::CheckAlignment;
use rustc_data_structures::fx::FxHashSet;
use rustc_hir::def::DefKind;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;
@ -151,12 +152,17 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
pub struct ConstPropMachine<'mir, 'tcx> {
/// The virtual call stack.
stack: Vec<Frame<'mir, 'tcx>>,
pub written_only_inside_own_block_locals: FxHashSet<Local>,
pub can_const_prop: IndexVec<Local, ConstPropMode>,
}
impl ConstPropMachine<'_, '_> {
pub fn new(can_const_prop: IndexVec<Local, ConstPropMode>) -> Self {
Self { stack: Vec::new(), can_const_prop }
Self {
stack: Vec::new(),
written_only_inside_own_block_locals: Default::default(),
can_const_prop,
}
}
}
@ -249,7 +255,10 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
"tried to write to a local that is marked as not propagatable"
)
}
ConstPropMode::OnlyInsideOwnBlock | ConstPropMode::FullConstProp => {}
ConstPropMode::OnlyInsideOwnBlock => {
ecx.machine.written_only_inside_own_block_locals.insert(local);
}
ConstPropMode::FullConstProp => {}
}
ecx.machine.stack[frame].locals[local].access_mut()
}
@ -416,6 +425,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
fn remove_const(ecx: &mut InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>, local: Local) {
ecx.frame_mut().locals[local].value =
LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit));
ecx.machine.written_only_inside_own_block_locals.remove(&local);
}
/// Returns the value, if any, of evaluating `c`.
@ -693,7 +703,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
}
}
fn ensure_not_propagated(&mut self, local: Local) {
fn ensure_not_propagated(&self, local: Local) {
if cfg!(debug_assertions) {
assert!(
self.get_const(local.into()).is_none()
@ -963,17 +973,30 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
// We remove all Locals which are restricted in propagation to their containing blocks and
// which were modified in the current block.
// Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`.
let can_const_prop = std::mem::take(&mut self.ecx.machine.can_const_prop);
for (local, &mode) in can_const_prop.iter_enumerated() {
let mut written_only_inside_own_block_locals =
std::mem::take(&mut self.ecx.machine.written_only_inside_own_block_locals);
// This loop can get very hot for some bodies: it check each local in each bb.
// To avoid this quadratic behaviour, we only clear the locals that were modified inside
// the current block.
for local in written_only_inside_own_block_locals.drain() {
debug_assert_eq!(
self.ecx.machine.can_const_prop[local],
ConstPropMode::OnlyInsideOwnBlock
);
Self::remove_const(&mut self.ecx, local);
}
self.ecx.machine.written_only_inside_own_block_locals =
written_only_inside_own_block_locals;
#[cfg(debug_assertions)]
for (local, &mode) in self.ecx.machine.can_const_prop.iter_enumerated() {
match mode {
ConstPropMode::FullConstProp => {}
ConstPropMode::NoPropagation => self.ensure_not_propagated(local),
ConstPropMode::OnlyInsideOwnBlock => {
Self::remove_const(&mut self.ecx, local);
ConstPropMode::NoPropagation | ConstPropMode::OnlyInsideOwnBlock => {
self.ensure_not_propagated(local);
}
}
}
self.ecx.machine.can_const_prop = can_const_prop;
}
}

28
compiler/rustc_mir_transform/src/const_prop_lint.rs
View File

@ -247,6 +247,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
fn remove_const(ecx: &mut InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>, local: Local) {
ecx.frame_mut().locals[local].value =
LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit));
ecx.machine.written_only_inside_own_block_locals.remove(&local);
}
fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
@ -484,7 +485,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
Some(())
}
fn ensure_not_propagated(&mut self, local: Local) {
fn ensure_not_propagated(&self, local: Local) {
if cfg!(debug_assertions) {
assert!(
self.get_const(local.into()).is_none()
@ -691,17 +692,30 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
// We remove all Locals which are restricted in propagation to their containing blocks and
// which were modified in the current block.
// Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`.
let can_const_prop = std::mem::take(&mut self.ecx.machine.can_const_prop);
for (local, &mode) in can_const_prop.iter_enumerated() {
let mut written_only_inside_own_block_locals =
std::mem::take(&mut self.ecx.machine.written_only_inside_own_block_locals);
// This loop can get very hot for some bodies: it check each local in each bb.
// To avoid this quadratic behaviour, we only clear the locals that were modified inside
// the current block.
for local in written_only_inside_own_block_locals.drain() {
debug_assert_eq!(
self.ecx.machine.can_const_prop[local],
ConstPropMode::OnlyInsideOwnBlock
);
Self::remove_const(&mut self.ecx, local);
}
self.ecx.machine.written_only_inside_own_block_locals =
written_only_inside_own_block_locals;
#[cfg(debug_assertions)]
for (local, &mode) in self.ecx.machine.can_const_prop.iter_enumerated() {
match mode {
ConstPropMode::FullConstProp => {}
ConstPropMode::NoPropagation => self.ensure_not_propagated(local),
ConstPropMode::OnlyInsideOwnBlock => {
Self::remove_const(&mut self.ecx, local);
ConstPropMode::NoPropagation | ConstPropMode::OnlyInsideOwnBlock => {
self.ensure_not_propagated(local);
}
}
}
self.ecx.machine.can_const_prop = can_const_prop;
}
}