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Refactor single variant Candidate enum into a struct
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`Candidate` enum has only a single `Ref` variant.  Refactor it into a
struct and reduce overall indentation of the code by two levels.

No functional changes.
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@tmiasko
tmiasko committed Nov 5, 2021
1 parent 045612b commit 7bc827b
Showing 1 changed file with 82 additions and 95 deletions.
177 changes: 82 additions & 95 deletions compiler/rustc_const_eval/src/transform/promote_consts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -93,16 +93,13 @@ impl TempState {
/// returned value in a promoted MIR, unless it's a subset
/// of a larger candidate.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum Candidate {
/// Borrow of a constant temporary, candidate for lifetime extension.
Ref(Location),
pub struct Candidate {
location: Location,
}

impl Candidate {
fn source_info(&self, body: &Body<'_>) -> SourceInfo {
match self {
Candidate::Ref(location) => *body.source_info(*location),
}
*body.source_info(self.location)
}
}

Expand Down Expand Up @@ -167,7 +164,7 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {

match *rvalue {
Rvalue::Ref(..) => {
self.candidates.push(Candidate::Ref(location));
self.candidates.push(Candidate { location });
}
_ => {}
}
Expand Down Expand Up @@ -209,36 +206,33 @@ struct Unpromotable;

impl<'tcx> Validator<'_, 'tcx> {
fn validate_candidate(&self, candidate: Candidate) -> Result<(), Unpromotable> {
match candidate {
Candidate::Ref(loc) => {
let statement = &self.body[loc.block].statements[loc.statement_index];
match &statement.kind {
StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
// We can only promote interior borrows of promotable temps (non-temps
// don't get promoted anyway).
self.validate_local(place.local)?;

// The reference operation itself must be promotable.
// (Needs to come after `validate_local` to avoid ICEs.)
self.validate_ref(*kind, place)?;

// We do not check all the projections (they do not get promoted anyway),
// but we do stay away from promoting anything involving a dereference.
if place.projection.contains(&ProjectionElem::Deref) {
return Err(Unpromotable);
}
let loc = candidate.location;
let statement = &self.body[loc.block].statements[loc.statement_index];
match &statement.kind {
StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
// We can only promote interior borrows of promotable temps (non-temps
// don't get promoted anyway).
self.validate_local(place.local)?;

// The reference operation itself must be promotable.
// (Needs to come after `validate_local` to avoid ICEs.)
self.validate_ref(*kind, place)?;

// We cannot promote things that need dropping, since the promoted value
// would not get dropped.
if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
return Err(Unpromotable);
}
// We do not check all the projections (they do not get promoted anyway),
// but we do stay away from promoting anything involving a dereference.
if place.projection.contains(&ProjectionElem::Deref) {
return Err(Unpromotable);
}

Ok(())
}
_ => bug!(),
// We cannot promote things that need dropping, since the promoted value
// would not get dropped.
if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
return Err(Unpromotable);
}

Ok(())
}
_ => bug!(),
}
}

Expand Down Expand Up @@ -871,58 +865,55 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
}))
};
let (blocks, local_decls) = self.source.basic_blocks_and_local_decls_mut();
match candidate {
Candidate::Ref(loc) => {
let statement = &mut blocks[loc.block].statements[loc.statement_index];
match statement.kind {
StatementKind::Assign(box (
_,
Rvalue::Ref(ref mut region, borrow_kind, ref mut place),
)) => {
// Use the underlying local for this (necessarily interior) borrow.
let ty = local_decls.local_decls()[place.local].ty;
let span = statement.source_info.span;

let ref_ty = tcx.mk_ref(
tcx.lifetimes.re_erased,
ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() },
);

*region = tcx.lifetimes.re_erased;

let mut projection = vec![PlaceElem::Deref];
projection.extend(place.projection);
place.projection = tcx.intern_place_elems(&projection);

// Create a temp to hold the promoted reference.
// This is because `*r` requires `r` to be a local,
// otherwise we would use the `promoted` directly.
let mut promoted_ref = LocalDecl::new(ref_ty, span);
promoted_ref.source_info = statement.source_info;
let promoted_ref = local_decls.push(promoted_ref);
assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);

let promoted_ref_statement = Statement {
source_info: statement.source_info,
kind: StatementKind::Assign(Box::new((
Place::from(promoted_ref),
Rvalue::Use(promoted_operand(ref_ty, span)),
))),
};
self.extra_statements.push((loc, promoted_ref_statement));

Rvalue::Ref(
tcx.lifetimes.re_erased,
borrow_kind,
Place {
local: mem::replace(&mut place.local, promoted_ref),
projection: List::empty(),
},
)
}
_ => bug!(),
}
let loc = candidate.location;
let statement = &mut blocks[loc.block].statements[loc.statement_index];
match statement.kind {
StatementKind::Assign(box (
_,
Rvalue::Ref(ref mut region, borrow_kind, ref mut place),
)) => {
// Use the underlying local for this (necessarily interior) borrow.
let ty = local_decls.local_decls()[place.local].ty;
let span = statement.source_info.span;

let ref_ty = tcx.mk_ref(
tcx.lifetimes.re_erased,
ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() },
);

*region = tcx.lifetimes.re_erased;

let mut projection = vec![PlaceElem::Deref];
projection.extend(place.projection);
place.projection = tcx.intern_place_elems(&projection);

// Create a temp to hold the promoted reference.
// This is because `*r` requires `r` to be a local,
// otherwise we would use the `promoted` directly.
let mut promoted_ref = LocalDecl::new(ref_ty, span);
promoted_ref.source_info = statement.source_info;
let promoted_ref = local_decls.push(promoted_ref);
assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);

let promoted_ref_statement = Statement {
source_info: statement.source_info,
kind: StatementKind::Assign(Box::new((
Place::from(promoted_ref),
Rvalue::Use(promoted_operand(ref_ty, span)),
))),
};
self.extra_statements.push((loc, promoted_ref_statement));

Rvalue::Ref(
tcx.lifetimes.re_erased,
borrow_kind,
Place {
local: mem::replace(&mut place.local, promoted_ref),
projection: List::empty(),
},
)
}
_ => bug!(),
}
};

Expand Down Expand Up @@ -964,17 +955,13 @@ pub fn promote_candidates<'tcx>(

let mut extra_statements = vec![];
for candidate in candidates.into_iter().rev() {
match candidate {
Candidate::Ref(Location { block, statement_index }) => {
if let StatementKind::Assign(box (place, _)) =
&body[block].statements[statement_index].kind
{
if let Some(local) = place.as_local() {
if temps[local] == TempState::PromotedOut {
// Already promoted.
continue;
}
}
let Location { block, statement_index } = candidate.location;
if let StatementKind::Assign(box (place, _)) = &body[block].statements[statement_index].kind
{
if let Some(local) = place.as_local() {
if temps[local] == TempState::PromotedOut {
// Already promoted.
continue;
}
}
}
Expand Down

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