bjoernager/rust
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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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28
compiler/rustc_mir_transform/src/const_prop_lint.rs
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@ -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;
}
}