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Fix liveness analysis for yield terminators

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A resume place is evaluated and assigned to only after a yield
terminator resumes. Ensure that locals used when evaluating the
resume place are live across the yield.
This commit is contained in:
Tomasz Miąsko 2022-08-01 00:00:00 +00:00
parent 5462da52ba
commit 31d892a942
1 changed files with 62 additions and 33 deletions
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95
compiler/rustc_mir_dataflow/src/impls/liveness.rs
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@ -23,12 +23,6 @@ use crate::{Analysis, AnalysisDomain, Backward, CallReturnPlaces, GenKill, GenKi
/// [liveness]: https://en.wikipedia.org/wiki/Live_variable_analysis
pub struct MaybeLiveLocals;
impl MaybeLiveLocals {
fn transfer_function<'a, T>(&self, trans: &'a mut T) -> TransferFunction<'a, T> {
TransferFunction(trans)
}
}
impl<'tcx> AnalysisDomain<'tcx> for MaybeLiveLocals {
type Domain = ChunkedBitSet<Local>;
type Direction = Backward;
@ -54,7 +48,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeLiveLocals {
statement: &mir::Statement<'tcx>,
location: Location,
) {
self.transfer_function(trans).visit_statement(statement, location);
TransferFunction(trans).visit_statement(statement, location);
}
fn terminator_effect(
@ -63,7 +57,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeLiveLocals {
terminator: &mir::Terminator<'tcx>,
location: Location,
) {
self.transfer_function(trans).visit_terminator(terminator, location);
TransferFunction(trans).visit_terminator(terminator, location);
}
fn call_return_effect(
@ -85,9 +79,11 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeLiveLocals {
_resume_block: mir::BasicBlock,
resume_place: mir::Place<'tcx>,
) {
if let Some(local) = resume_place.as_local() {
trans.kill(local);
}
YieldResumeEffect(trans).visit_place(
&resume_place,
PlaceContext::MutatingUse(MutatingUseContext::Yield),
Location::START,
)
}
}
@ -98,23 +94,58 @@ where
T: GenKill<Local>,
{
fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) {
let local = place.local;
// We purposefully do not call `super_place` here to avoid calling `visit_local` for this
// place with one of the `Projection` variants of `PlaceContext`.
self.visit_projection(place.as_ref(), context, location);
if let PlaceContext::MutatingUse(MutatingUseContext::Yield) = context {
// The resume place is evaluated and assigned to only after generator resumes, so its
// effect is handled separately in `yield_resume_effect`.
return;
}
match DefUse::for_place(*place, context) {
Some(DefUse::Def) => {
if let PlaceContext::MutatingUse(
MutatingUseContext::Call | MutatingUseContext::AsmOutput,
) = context
{
// For the associated terminators, this is only a `Def` when the terminator returns
// "successfully." As such, we handle this case separately in `call_return_effect`
// above. However, if the place looks like `*_5`, this is still unconditionally a use of
// `_5`.
} else {
self.0.kill(place.local);
}
}
Some(DefUse::Use) => self.0.gen(place.local),
None => {}
}
self.visit_projection(place.as_ref(), context, location);
}
fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
match DefUse::for_place(local.into(), context) {
Some(DefUse::Def) => self.0.kill(local),
Some(DefUse::Use) => self.0.gen(local),
None => {}
}
}
}
struct YieldResumeEffect<'a, T>(&'a mut T);
impl<'tcx, T> Visitor<'tcx> for YieldResumeEffect<'_, T>
where
T: GenKill<Local>,
{
fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) {
match DefUse::for_place(*place, context) {
Some(DefUse::Def) => self.0.kill(place.local),
Some(DefUse::Use) => self.0.gen(place.local),
None => {}
}
self.visit_projection(place.as_ref(), context, location);
}
fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
// Because we do not call `super_place` above, `visit_local` is only called for locals that
// do not appear as part of a `Place` in the MIR. This handles cases like the implicit use
// of the return place in a `Return` terminator or the index in an `Index` projection.
match DefUse::for_place(local.into(), context) {
Some(DefUse::Def) => self.0.kill(local),
Some(DefUse::Use) => self.0.gen(local),
@ -134,7 +165,13 @@ impl DefUse {
match context {
PlaceContext::NonUse(_) => None,
PlaceContext::MutatingUse(MutatingUseContext::Store | MutatingUseContext::Deinit) => {
PlaceContext::MutatingUse(
MutatingUseContext::Call
| MutatingUseContext::Yield
| MutatingUseContext::AsmOutput
| MutatingUseContext::Store
| MutatingUseContext::Deinit,
) => {
if place.is_indirect() {
// Treat derefs as a use of the base local. `*p = 4` is not a def of `p` but a
// use.
@ -152,16 +189,6 @@ impl DefUse {
place.is_indirect().then_some(DefUse::Use)
}
// For the associated terminators, this is only a `Def` when the terminator returns
// "successfully." As such, we handle this case separately in `call_return_effect`
// above. However, if the place looks like `*_5`, this is still unconditionally a use of
// `_5`.
PlaceContext::MutatingUse(
MutatingUseContext::Call
| MutatingUseContext::Yield
| MutatingUseContext::AsmOutput,
) => place.is_indirect().then_some(DefUse::Use),
// All other contexts are uses...
PlaceContext::MutatingUse(
MutatingUseContext::AddressOf
@ -290,8 +317,10 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeTransitiveLiveLocals<'a> {
_resume_block: mir::BasicBlock,
resume_place: mir::Place<'tcx>,
) {
if let Some(local) = resume_place.as_local() {
trans.remove(local);
}
YieldResumeEffect(trans).visit_place(
&resume_place,
PlaceContext::MutatingUse(MutatingUseContext::Yield),
Location::START,
)
}
}