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Use correct place for enum_place

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PR #69562, which fixed a bug that was causing clippy to ICE, passed the
place for the *result* of `Rvalue::Discriminant` instead of the
*operand* to `apply_discriminant_switch_effect`. As a result, no effect
was applied at all, and we lost the perf benefits from marking
inactive enum variants as uninitialized.
This commit is contained in:
Dylan MacKenzie 2020-03-03 11:26:51 -08:00
parent b135c739fb
commit e82ec2315e
1 changed files with 28 additions and 20 deletions
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48
src/librustc_mir/dataflow/generic/engine.rs
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@ -239,23 +239,26 @@ where
}
SwitchInt { ref targets, ref values, ref discr, .. } => {
// If this is a switch on an enum discriminant, a custom effect may be applied
// along each outgoing edge.
if let Some(place) = discr.place() {
let enum_def = switch_on_enum_discriminant(self.tcx, self.body, bb_data, place);
if let Some(enum_def) = enum_def {
let Engine { tcx, body, .. } = *self;
let enum_ = discr
.place()
.and_then(|discr| switch_on_enum_discriminant(tcx, body, bb_data, discr));
match enum_ {
// If this is a switch on an enum discriminant, a custom effect may be applied
// along each outgoing edge.
Some((enum_place, enum_def)) => {
self.propagate_bits_into_enum_discriminant_switch_successors(
in_out, bb, enum_def, place, dirty_list, &*values, &*targets,
in_out, bb, enum_def, enum_place, dirty_list, &*values, &*targets,
);
return;
}
}
// Otherwise, it's just a normal `SwitchInt`, and every successor sees the same
// exit state.
for target in targets.iter().copied() {
self.propagate_bits_into_entry_set_for(&in_out, target, dirty_list);
// Otherwise, it's just a normal `SwitchInt`, and every successor sees the same
// exit state.
None => {
for target in targets.iter().copied() {
self.propagate_bits_into_entry_set_for(&in_out, target, dirty_list);
}
}
}
}
@ -342,22 +345,27 @@ where
}
}
/// Look at the last statement of a block that ends with to see if it is an assignment of an enum
/// discriminant to the local that determines the target of a `SwitchInt` like so:
/// _42 = discriminant(..)
/// Inspect a `SwitchInt`-terminated basic block to see if the condition of that `SwitchInt` is
/// an enum discriminant.
///
/// We expect such blocks to have a call to `discriminant` as their last statement like so:
/// _42 = discriminant(_1)
/// SwitchInt(_42, ..)
///
/// If the basic block matches this pattern, this function returns the place corresponding to the
/// enum (`_1` in the example above) as well as the `AdtDef` of that enum.
fn switch_on_enum_discriminant(
tcx: TyCtxt<'tcx>,
body: &mir::Body<'tcx>,
block: &mir::BasicBlockData<'tcx>,
body: &'mir mir::Body<'tcx>,
block: &'mir mir::BasicBlockData<'tcx>,
switch_on: &mir::Place<'tcx>,
) -> Option<&'tcx ty::AdtDef> {
) -> Option<(&'mir mir::Place<'tcx>, &'tcx ty::AdtDef)> {
match block.statements.last().map(|stmt| &stmt.kind) {
Some(mir::StatementKind::Assign(box (lhs, mir::Rvalue::Discriminant(discriminated))))
if lhs == switch_on =>
{
match &discriminated.ty(body, tcx).ty.kind {
ty::Adt(def, _) => Some(def),
ty::Adt(def, _) => Some((discriminated, def)),
// `Rvalue::Discriminant` is also used to get the active yield point for a
// generator, but we do not need edge-specific effects in that case. This may