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Rollup merge of rust-lang#70658 - davidtwco:issue-70285-still-further…
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…-specializable, r=eddyb

add `STILL_FURTHER_SPECIALIZABLE` flag

Contributes to rust-lang#70285.

This PR adds a `STILL_FURTHER_SPECIALIZABLE` flag to `TypeFlags`
which replaces `needs_infer` and `needs_subst` in `Instance::resolve`
and `assemble_candidates_from_impls`.

r? @eddyb
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@Centril
Centril authored Apr 2, 2020
2 parents 43b536e + c665eae commit 921bf33
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Showing 6 changed files with 86 additions and 57 deletions.
16 changes: 13 additions & 3 deletions src/librustc_middle/ty/flags.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use crate::ty::subst::{GenericArgKind, SubstsRef};
use crate::ty::subst::{GenericArg, GenericArgKind};
use crate::ty::{self, InferConst, Ty, TypeFlags};

#[derive(Debug)]
Expand Down Expand Up @@ -81,6 +81,7 @@ impl FlagComputation {

&ty::Param(_) => {
self.add_flags(TypeFlags::HAS_TY_PARAM);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
}

&ty::Generator(_, ref substs, _) => {
Expand All @@ -99,14 +100,17 @@ impl FlagComputation {

&ty::Bound(debruijn, _) => {
self.add_binder(debruijn);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
}

&ty::Placeholder(..) => {
self.add_flags(TypeFlags::HAS_TY_PLACEHOLDER);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
}

&ty::Infer(infer) => {
self.add_flags(TypeFlags::HAS_TY_INFER);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
match infer {
ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {}

Expand Down Expand Up @@ -218,17 +222,23 @@ impl FlagComputation {
}
ty::ConstKind::Infer(infer) => {
self.add_flags(TypeFlags::HAS_CT_INFER);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
match infer {
InferConst::Fresh(_) => {}
InferConst::Var(_) => self.add_flags(TypeFlags::KEEP_IN_LOCAL_TCX),
}
}
ty::ConstKind::Bound(debruijn, _) => self.add_binder(debruijn),
ty::ConstKind::Bound(debruijn, _) => {
self.add_binder(debruijn);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
}
ty::ConstKind::Param(_) => {
self.add_flags(TypeFlags::HAS_CT_PARAM);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
}
ty::ConstKind::Placeholder(_) => {
self.add_flags(TypeFlags::HAS_CT_PLACEHOLDER);
self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
}
ty::ConstKind::Value(_) => {}
}
Expand All @@ -243,7 +253,7 @@ impl FlagComputation {
self.add_substs(projection_ty.substs);
}

fn add_substs(&mut self, substs: SubstsRef<'_>) {
fn add_substs(&mut self, substs: &[GenericArg<'_>]) {
for kind in substs {
match kind.unpack() {
GenericArgKind::Type(ty) => self.add_ty(ty),
Expand Down
7 changes: 7 additions & 0 deletions src/librustc_middle/ty/fold.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,13 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
}

/// Indicates whether this value still has parameters/placeholders/inference variables
/// which could be replaced later, in a way that would change the results of `impl`
/// specialization.
fn still_further_specializable(&self) -> bool {
self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
}

/// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
pub struct Visitor<F>(F);
Expand Down
109 changes: 57 additions & 52 deletions src/librustc_middle/ty/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -524,101 +524,106 @@ bitflags! {
// Does this have parameters? Used to determine whether substitution is
// required.
/// Does this have [Param]?
const HAS_TY_PARAM = 1 << 0;
const HAS_TY_PARAM = 1 << 0;
/// Does this have [ReEarlyBound]?
const HAS_RE_PARAM = 1 << 1;
const HAS_RE_PARAM = 1 << 1;
/// Does this have [ConstKind::Param]?
const HAS_CT_PARAM = 1 << 2;
const HAS_CT_PARAM = 1 << 2;

const NEEDS_SUBST = TypeFlags::HAS_TY_PARAM.bits
| TypeFlags::HAS_RE_PARAM.bits
| TypeFlags::HAS_CT_PARAM.bits;
const NEEDS_SUBST = TypeFlags::HAS_TY_PARAM.bits
| TypeFlags::HAS_RE_PARAM.bits
| TypeFlags::HAS_CT_PARAM.bits;

/// Does this have [Infer]?
const HAS_TY_INFER = 1 << 3;
const HAS_TY_INFER = 1 << 3;
/// Does this have [ReVar]?
const HAS_RE_INFER = 1 << 4;
const HAS_RE_INFER = 1 << 4;
/// Does this have [ConstKind::Infer]?
const HAS_CT_INFER = 1 << 5;
const HAS_CT_INFER = 1 << 5;

/// Does this have inference variables? Used to determine whether
/// inference is required.
const NEEDS_INFER = TypeFlags::HAS_TY_INFER.bits
| TypeFlags::HAS_RE_INFER.bits
| TypeFlags::HAS_CT_INFER.bits;
const NEEDS_INFER = TypeFlags::HAS_TY_INFER.bits
| TypeFlags::HAS_RE_INFER.bits
| TypeFlags::HAS_CT_INFER.bits;

/// Does this have [Placeholder]?
const HAS_TY_PLACEHOLDER = 1 << 6;
const HAS_TY_PLACEHOLDER = 1 << 6;
/// Does this have [RePlaceholder]?
const HAS_RE_PLACEHOLDER = 1 << 7;
const HAS_RE_PLACEHOLDER = 1 << 7;
/// Does this have [ConstKind::Placeholder]?
const HAS_CT_PLACEHOLDER = 1 << 8;
const HAS_CT_PLACEHOLDER = 1 << 8;

/// `true` if there are "names" of regions and so forth
/// that are local to a particular fn/inferctxt
const HAS_FREE_LOCAL_REGIONS = 1 << 9;
const HAS_FREE_LOCAL_REGIONS = 1 << 9;

/// `true` if there are "names" of types and regions and so forth
/// that are local to a particular fn
const HAS_FREE_LOCAL_NAMES = TypeFlags::HAS_TY_PARAM.bits
| TypeFlags::HAS_CT_PARAM.bits
| TypeFlags::HAS_TY_INFER.bits
| TypeFlags::HAS_CT_INFER.bits
| TypeFlags::HAS_TY_PLACEHOLDER.bits
| TypeFlags::HAS_CT_PLACEHOLDER.bits
| TypeFlags::HAS_FREE_LOCAL_REGIONS.bits;
const HAS_FREE_LOCAL_NAMES = TypeFlags::HAS_TY_PARAM.bits
| TypeFlags::HAS_CT_PARAM.bits
| TypeFlags::HAS_TY_INFER.bits
| TypeFlags::HAS_CT_INFER.bits
| TypeFlags::HAS_TY_PLACEHOLDER.bits
| TypeFlags::HAS_CT_PLACEHOLDER.bits
| TypeFlags::HAS_FREE_LOCAL_REGIONS.bits;

/// Does this have [Projection] or [UnnormalizedProjection]?
const HAS_TY_PROJECTION = 1 << 10;
const HAS_TY_PROJECTION = 1 << 10;
/// Does this have [Opaque]?
const HAS_TY_OPAQUE = 1 << 11;
const HAS_TY_OPAQUE = 1 << 11;
/// Does this have [ConstKind::Unevaluated]?
const HAS_CT_PROJECTION = 1 << 12;
const HAS_CT_PROJECTION = 1 << 12;

/// Could this type be normalized further?
const HAS_PROJECTION = TypeFlags::HAS_TY_PROJECTION.bits
| TypeFlags::HAS_TY_OPAQUE.bits
| TypeFlags::HAS_CT_PROJECTION.bits;
const HAS_PROJECTION = TypeFlags::HAS_TY_PROJECTION.bits
| TypeFlags::HAS_TY_OPAQUE.bits
| TypeFlags::HAS_CT_PROJECTION.bits;

/// Present if the type belongs in a local type context.
/// Set for placeholders and inference variables that are not "Fresh".
const KEEP_IN_LOCAL_TCX = 1 << 13;
const KEEP_IN_LOCAL_TCX = 1 << 13;

/// Is an error type reachable?
const HAS_TY_ERR = 1 << 14;
const HAS_TY_ERR = 1 << 14;

/// Does this have any region that "appears free" in the type?
/// Basically anything but [ReLateBound] and [ReErased].
const HAS_FREE_REGIONS = 1 << 15;
const HAS_FREE_REGIONS = 1 << 15;

/// Does this have any [ReLateBound] regions? Used to check
/// if a global bound is safe to evaluate.
const HAS_RE_LATE_BOUND = 1 << 16;
const HAS_RE_LATE_BOUND = 1 << 16;

/// Does this have any [ReErased] regions?
const HAS_RE_ERASED = 1 << 17;
const HAS_RE_ERASED = 1 << 17;

/// Does this value have parameters/placeholders/inference variables which could be
/// replaced later, in a way that would change the results of `impl` specialization?
const STILL_FURTHER_SPECIALIZABLE = 1 << 18;

/// Flags representing the nominal content of a type,
/// computed by FlagsComputation. If you add a new nominal
/// flag, it should be added here too.
const NOMINAL_FLAGS = TypeFlags::HAS_TY_PARAM.bits
| TypeFlags::HAS_RE_PARAM.bits
| TypeFlags::HAS_CT_PARAM.bits
| TypeFlags::HAS_TY_INFER.bits
| TypeFlags::HAS_RE_INFER.bits
| TypeFlags::HAS_CT_INFER.bits
| TypeFlags::HAS_TY_PLACEHOLDER.bits
| TypeFlags::HAS_RE_PLACEHOLDER.bits
| TypeFlags::HAS_CT_PLACEHOLDER.bits
| TypeFlags::HAS_FREE_LOCAL_REGIONS.bits
| TypeFlags::HAS_TY_PROJECTION.bits
| TypeFlags::HAS_TY_OPAQUE.bits
| TypeFlags::HAS_CT_PROJECTION.bits
| TypeFlags::KEEP_IN_LOCAL_TCX.bits
| TypeFlags::HAS_TY_ERR.bits
| TypeFlags::HAS_FREE_REGIONS.bits
| TypeFlags::HAS_RE_LATE_BOUND.bits
| TypeFlags::HAS_RE_ERASED.bits;
const NOMINAL_FLAGS = TypeFlags::HAS_TY_PARAM.bits
| TypeFlags::HAS_RE_PARAM.bits
| TypeFlags::HAS_CT_PARAM.bits
| TypeFlags::HAS_TY_INFER.bits
| TypeFlags::HAS_RE_INFER.bits
| TypeFlags::HAS_CT_INFER.bits
| TypeFlags::HAS_TY_PLACEHOLDER.bits
| TypeFlags::HAS_RE_PLACEHOLDER.bits
| TypeFlags::HAS_CT_PLACEHOLDER.bits
| TypeFlags::HAS_FREE_LOCAL_REGIONS.bits
| TypeFlags::HAS_TY_PROJECTION.bits
| TypeFlags::HAS_TY_OPAQUE.bits
| TypeFlags::HAS_CT_PROJECTION.bits
| TypeFlags::KEEP_IN_LOCAL_TCX.bits
| TypeFlags::HAS_TY_ERR.bits
| TypeFlags::HAS_FREE_REGIONS.bits
| TypeFlags::HAS_RE_LATE_BOUND.bits
| TypeFlags::HAS_RE_ERASED.bits
| TypeFlags::STILL_FURTHER_SPECIALIZABLE.bits;
}
}

Expand Down
3 changes: 3 additions & 0 deletions src/librustc_middle/ty/sty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1623,16 +1623,19 @@ impl RegionKind {
flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
flags = flags | TypeFlags::HAS_RE_INFER;
flags = flags | TypeFlags::KEEP_IN_LOCAL_TCX;
flags = flags | TypeFlags::STILL_FURTHER_SPECIALIZABLE;
}
ty::RePlaceholder(..) => {
flags = flags | TypeFlags::HAS_FREE_REGIONS;
flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
flags = flags | TypeFlags::HAS_RE_PLACEHOLDER;
flags = flags | TypeFlags::STILL_FURTHER_SPECIALIZABLE;
}
ty::ReEarlyBound(..) => {
flags = flags | TypeFlags::HAS_FREE_REGIONS;
flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
flags = flags | TypeFlags::HAS_RE_PARAM;
flags = flags | TypeFlags::STILL_FURTHER_SPECIALIZABLE;
}
ty::ReFree { .. } | ty::ReScope { .. } => {
flags = flags | TypeFlags::HAS_FREE_REGIONS;
Expand Down
2 changes: 1 addition & 1 deletion src/librustc_trait_selection/traits/project.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1028,7 +1028,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
// assume `poly_trait_ref` isn't monomorphic, if it contains any.
let poly_trait_ref =
selcx.infcx().resolve_vars_if_possible(&poly_trait_ref);
!poly_trait_ref.needs_infer() && !poly_trait_ref.needs_subst()
!poly_trait_ref.still_further_specializable()
} else {
debug!(
"assemble_candidates_from_impls: not eligible due to default: \
Expand Down
6 changes: 5 additions & 1 deletion src/librustc_ty/instance.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -127,7 +127,11 @@ fn resolve_associated_item<'tcx>(
// and the obligation is monomorphic, otherwise passes such as
// transmute checking and polymorphic MIR optimizations could
// get a result which isn't correct for all monomorphizations.
if param_env.reveal == Reveal::All { !trait_ref.needs_subst() } else { false }
if param_env.reveal == Reveal::All {
!trait_ref.still_further_specializable()
} else {
false
}
};

if !eligible {
Expand Down

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