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polymorphize: I used if T used in I: Foo<T>
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This commit adjusts polymorphization's handling of predicates so that
after ensuring that `T` is used in `I: Foo<T>` if `I` is used, it now
ensures that `I` is used if `T` is used in `I: Foo<T>`. This is
necessary to mark generic parameters that only exist in impl parameters
as used - thereby avoiding symbol clashes when using the new mangling
scheme.

Signed-off-by: David Wood <[email protected]>
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@davidtwco
davidtwco committed Aug 14, 2020
1 parent 3fbed17 commit bf3ef26
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Showing 3 changed files with 189 additions and 31 deletions.
150 changes: 119 additions & 31 deletions src/librustc_mir/monomorphize/polymorphize.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -69,8 +69,7 @@ fn unused_generic_params(tcx: TyCtxt<'_>, def_id: DefId) -> FiniteBitSet<u32> {

// Visit MIR and accumululate used generic parameters.
let body = tcx.optimized_mir(def_id);
let mut vis =
UsedGenericParametersVisitor { tcx, def_id, unused_parameters: &mut unused_parameters };
let mut vis = MarkUsedGenericParams { tcx, def_id, unused_parameters: &mut unused_parameters };
vis.visit_body(body);
debug!("unused_generic_params: (after visitor) unused_parameters={:?}", unused_parameters);

Expand Down Expand Up @@ -120,45 +119,101 @@ fn mark_used_by_predicates<'tcx>(
def_id: DefId,
unused_parameters: &mut FiniteBitSet<u32>,
) {
let def_id = tcx.closure_base_def_id(def_id);

let is_self_ty_used = |unused_parameters: &mut FiniteBitSet<u32>, self_ty: Ty<'tcx>| {
debug!("unused_generic_params: self_ty={:?}", self_ty);
if let ty::Param(param) = self_ty.kind {
!unused_parameters.contains(param.index).unwrap_or(false)
} else {
false
}
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 = UsedGenericParametersVisitor { tcx, def_id, unused_parameters };
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_parameters_used_in_predicates: predicates_of={:?}", predicates);
for (predicate, _) in predicates.predicates {
match predicate.skip_binders() {
ty::PredicateAtom::Trait(predicate, ..) => {
let trait_ref = predicate.trait_ref;
if is_self_ty_used(unused_parameters, trait_ref.self_ty()) {
debug!("mark_used_by_predicates: predicates_of={:?}", predicates);

let mut current_unused_parameters = FiniteBitSet::new_empty();
// Run to a fixed point to support `where T: Trait<U>, U: Trait<V>`, starting with an empty
// bit set so that this is skipped if all parameters are already used.
while current_unused_parameters != *unused_parameters {
debug!(
"mark_used_by_predicates: current_unused_parameters={:?} = unused_parameters={:?}",
current_unused_parameters, unused_parameters
);
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() {
debug!("unused_generic_params: (trait) ty={:?}", ty);
mark_ty(unused_parameters, ty);
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();
if is_self_ty_used(unused_parameters, self_ty) {
debug!("unused_generic_params: (projection ty={:?}", proj.ty);
mark_ty(unused_parameters, proj.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(..) => (),
}
_ => (),
}
}

if let Some(parent) = predicates.parent {
mark_used_by_predicates(tcx, parent, unused_parameters);
}
}

/// Emit errors for the function annotated by `#[rustc_polymorphize_error]`, labelling each generic
Expand Down Expand Up @@ -204,13 +259,13 @@ fn emit_unused_generic_params_error<'tcx>(
}

/// Visitor used to aggregate generic parameter uses.
struct UsedGenericParametersVisitor<'a, 'tcx> {
struct MarkUsedGenericParams<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
def_id: DefId,
unused_parameters: &'a mut FiniteBitSet<u32>,
}

impl<'a, 'tcx> UsedGenericParametersVisitor<'a, 'tcx> {
impl<'a, 'tcx> MarkUsedGenericParams<'a, 'tcx> {
/// Invoke `unused_generic_params` on a body contained within the current item (e.g.
/// a closure, generator or constant).
fn visit_child_body(&mut self, def_id: DefId, substs: SubstsRef<'tcx>) {
Expand All @@ -229,7 +284,7 @@ impl<'a, 'tcx> UsedGenericParametersVisitor<'a, 'tcx> {
}
}

impl<'a, 'tcx> Visitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
impl<'a, 'tcx> Visitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
debug!("visit_local_decl: local_decl={:?}", local_decl);
if local == Local::from_usize(1) {
Expand All @@ -256,7 +311,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
}
}

impl<'a, 'tcx> TypeVisitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
impl<'a, 'tcx> TypeVisitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> bool {
debug!("visit_const: c={:?}", c);
if !c.has_param_types_or_consts() {
Expand Down Expand Up @@ -318,3 +373,36 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
}
}
}

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

impl<'a, 'tcx> TypeVisitor<'tcx> for IsUsedGenericParams<'a> {
fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> bool {
debug!("visit_const: c={:?}", c);
if !c.has_param_types_or_consts() {
return false;
}

match c.val {
ty::ConstKind::Param(param) => {
!self.unused_parameters.contains(param.index).unwrap_or(false)
}
_ => c.super_visit_with(self),
}
}

fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
debug!("visit_ty: ty={:?}", ty);
if !ty.has_param_types_or_consts() {
return false;
}

match ty.kind {
ty::Param(param) => !self.unused_parameters.contains(param.index).unwrap_or(false),
_ => ty.super_visit_with(self),
}
}
}
48 changes: 48 additions & 0 deletions src/test/ui/polymorphization/predicates.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,55 @@ where
bar::<I>()
}

#[rustc_polymorphize_error]
fn baz<I, T>(_: I)
where
std::iter::Repeat<I>: Iterator<Item = T>,
{
bar::<I>()
}

// In addition, check that `I` is considered used in `next::{{closure}}`, because `T` is used and
// `T` is really just `I::Item`. `E` is used due to the fixed-point marking of predicates.

pub(crate) struct Foo<'a, I, E>(I, &'a E);

impl<'a, I, T: 'a, E> Iterator for Foo<'a, I, E>
where
I: Iterator<Item = &'a (T, E)>,
{
type Item = T;

#[rustc_polymorphize_error]
fn next(&mut self) -> Option<Self::Item> {
self.find(|_| true)
}
}

// Furthermore, check that `B` is considered used because `C` is used, and that `A` is considered
// used because `B` is now used.

trait Baz<Z> {}

impl Baz<u16> for u8 {}
impl Baz<u32> for u16 {}

#[rustc_polymorphize_error]
fn quux<A, B, C: Default>() -> usize
where
A: Baz<B>,
B: Baz<C>,
{
std::mem::size_of::<C>()
}

fn main() {
let x = &[2u32];
foo(x.iter());
baz(x.iter());

let mut a = Foo([(1u32, 1u16)].iter(), &1u16);
let _ = a.next();

let _ = quux::<u8, u16, u32>();
}
22 changes: 22 additions & 0 deletions src/test/ui/polymorphization/symbol-ambiguity.rs
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
// build-pass
// compile-flags: -Zpolymorphize=on -Zsymbol-mangling-version=v0

pub(crate) struct Foo<'a, I, E>(I, &'a E);

impl<'a, I, T: 'a, E> Iterator for Foo<'a, I, E>
where
I: Iterator<Item = &'a (T, E)>,
{
type Item = T;

fn next(&mut self) -> Option<Self::Item> {
self.find(|_| true)
}
}

fn main() {
let mut a = Foo([(1u32, 1u16)].iter(), &1u16);
let mut b = Foo([(1u16, 1u32)].iter(), &1u32);
let _ = a.next();
let _ = b.next();
}

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