Skip to content

polymorphize: if any param in a predicate is used, then all are used #75595

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Aug 20, 2020
Merged

polymorphize: if any param in a predicate is used, then all are used #75595

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
87 changes: 12 additions & 75 deletions src/librustc_mir/monomorphize/polymorphize.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -119,16 +119,6 @@ fn mark_used_by_predicates<'tcx>(
def_id: DefId,
unused_parameters: &mut FiniteBitSet<u32>,
) {
let is_ty_used = |unused_parameters: &FiniteBitSet<u32>, ty: Ty<'tcx>| -> bool {
let mut vis = IsUsedGenericParams { unused_parameters };
ty.visit_with(&mut vis)
};

let mark_ty = |unused_parameters: &mut FiniteBitSet<u32>, ty: Ty<'tcx>| {
let mut vis = MarkUsedGenericParams { tcx, def_id, unused_parameters };
ty.visit_with(&mut vis);
};

let def_id = tcx.closure_base_def_id(def_id);
let predicates = tcx.explicit_predicates_of(def_id);
debug!("mark_used_by_predicates: predicates_of={:?}", predicates);
Expand All @@ -144,69 +134,16 @@ fn mark_used_by_predicates<'tcx>(
current_unused_parameters = *unused_parameters;

for (predicate, _) in predicates.predicates {
match predicate.skip_binders() {
ty::PredicateAtom::Trait(predicate, ..) => {
let trait_ref = predicate.trait_ref;
debug!("mark_used_by_predicates: (trait) trait_ref={:?}", trait_ref);

// Consider `T` used if `I` is used in predicates of the form
// `I: Iterator<Item = T>`
debug!("mark_used_by_predicates: checking self");
if is_ty_used(unused_parameters, trait_ref.self_ty()) {
debug!("mark_used_by_predicates: used!");
for ty in trait_ref.substs.types() {
mark_ty(unused_parameters, ty);
}

// No need to check for a type being used in the substs if `self_ty` was
// used.
continue;
}

// Consider `I` used if `T` is used in predicates of the form
// `I: Iterator<Item = &'a (T, E)>` (see rust-lang/rust#75326)
debug!("mark_used_by_predicates: checking substs");
for ty in trait_ref.substs.types() {
if is_ty_used(unused_parameters, ty) {
debug!("mark_used_by_predicates: used!");
mark_ty(unused_parameters, trait_ref.self_ty());
}
}
}
ty::PredicateAtom::Projection(proj, ..) => {
let self_ty = proj.projection_ty.self_ty();
debug!(
"mark_used_by_predicates: (projection) self_ty={:?} proj.ty={:?}",
self_ty, proj.ty
);

// Consider `T` used if `I` is used in predicates of the form
// `<I as Iterator>::Item = T`
debug!("mark_used_by_predicates: checking self");
if is_ty_used(unused_parameters, self_ty) {
debug!("mark_used_by_predicates: used!");
mark_ty(unused_parameters, proj.ty);

// No need to check for projection type being used if `self_ty` was used.
continue;
}

// Consider `I` used if `T` is used in predicates of the form
// `<I as Iterator>::Item = &'a (T, E)` (see rust-lang/rust#75326)
debug!("mark_used_by_predicates: checking projection ty");
if is_ty_used(unused_parameters, proj.ty) {
debug!("mark_used_by_predicates: used!");
mark_ty(unused_parameters, self_ty);
}
}
ty::PredicateAtom::RegionOutlives(..)
| ty::PredicateAtom::TypeOutlives(..)
| ty::PredicateAtom::WellFormed(..)
| ty::PredicateAtom::ObjectSafe(..)
| ty::PredicateAtom::ClosureKind(..)
| ty::PredicateAtom::Subtype(..)
| ty::PredicateAtom::ConstEvaluatable(..)
| ty::PredicateAtom::ConstEquate(..) => (),
// Consider all generic params in a predicate as used if any other parameter in the
// predicate is used.
let any_param_used = {
let mut vis = HasUsedGenericParams { unused_parameters };
predicate.visit_with(&mut vis)
};

if any_param_used {
let mut vis = MarkUsedGenericParams { tcx, def_id, unused_parameters };
predicate.visit_with(&mut vis);
}
}
}
Expand Down Expand Up @@ -375,11 +312,11 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
}

/// Visitor used to check if a generic parameter is used.
struct IsUsedGenericParams<'a> {
struct HasUsedGenericParams<'a> {
unused_parameters: &'a FiniteBitSet<u32>,
}

impl<'a, 'tcx> TypeVisitor<'tcx> for IsUsedGenericParams<'a> {
impl<'a, 'tcx> TypeVisitor<'tcx> for HasUsedGenericParams<'a> {
fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> bool {
debug!("visit_const: c={:?}", c);
if !c.has_param_types_or_consts() {
Expand Down
17 changes: 17 additions & 0 deletions src/test/ui/polymorphization/predicates.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,21 @@ where
std::mem::size_of::<C>()
}

// Finally, check that `F` is considered used because `G` is used when neither are in the self-ty
// of the predicate.

trait Foobar<F, G> {}

impl Foobar<u32, u32> for () {}

#[rustc_polymorphize_error]
fn foobar<F, G>() -> usize
where
(): Foobar<F, G>,
{
std::mem::size_of::<G>()
}

fn main() {
let x = &[2u32];
foo(x.iter());
Expand All @@ -69,4 +84,6 @@ fn main() {
let _ = a.next();

let _ = quux::<u8, u16, u32>();

let _ = foobar::<u32, u32>();
}