This was a remnant of the old generics implementation, where
all nested types were expanded into an AllArchetypes list.
For quite some time, this method no longer returned *all*
dependent types, only those with generic requirements on
them, and all if its remaining uses were a bit convoluted.
- In the generic specialization code, we used this to mangle
substitutions for generic parameters that are not subject
to a concrete same-type constraint.
A new GenericSignature::getSubstitutableParams()
function handles this use-case instead. It is similar
to getGenericParams(), but only returns generic parameters
which require substitution.
In the future, SubstitutionLists will only store replacement
types for these generic parameters, instead of the list of
types that we used to produce from getAllDependentTypes().
- In specialization mangling and speculative devirtualization,
we relied on SubstitutionLists having the same size and
order as getAllDependentTypes(). It's better to turn the
SubstitutionList into a SubstitutionMap instead, and do lookups
into the map.
- In the SIL parser, we were making a pass over the generic
requirements before looking at getAllDependentTypes();
enumeratePairedRequirements() gives the correct information
upfront.
- In SIL box serialization, we don't serialize the size of the
substitution list, since it's available from the generic
signature. Add a GenericSignature::getSubstitutionListSize()
method, but that will go away soon once SubstitionList
serialization only serializes replacement types for generic
parameters.
- A few remaining uses now call enumeratePairedRequirements()
directly.
It turns out that GenericSignature::getAllDependentTypes() sometimes
includes generic type parameter types that have been made
concrete. Tolerate this for now, because fixing it causes issues
elsewhere.
These are no longer necessary now that we have combineSubstitutionMaps(),
and will not make sense once we switch to a more compact representation
for SubstitutionMap.
This method maps interface types to archetypes, which in general
requires a module for performing conformance lookups, if mapping
a member type of a generic parameter which has been made concrete.
However, in practice the types we are mapping here are all canonical
with respect to the generic signature, because they came from
GenericSignature::getAllDependentTypes(), so we actually don't need
to do conformance lookups.
This allows some code to be simplified.
SubstitutionList is going to be a more compact representation of
a SubstitutionMap, suitable for inline allocation inside another
object.
For now, it's just a typedef for ArrayRef<Substitution>.
Just like the recently-added GenericSignature::getSubstitutionMap(),
this takes a type substitution function and conformance lookup
function and produces a new SubstitionMap.
Introduce an algorithm to canonicalize and minimize same-type
constraints. The algorithm itself computes the equivalence classes
that would exist if all explicitly-provided same-type constraints are
ignored, and then forms a minimal, canonical set of explicit same-type
constraints to reform the actual equivalence class known to the type
checker. This should eliminate a number of problems we've seen with
inconsistently-chosen same-type constraints affecting
canonicalization.
Instead of creating an archetype builder with a module---which was
only used for protocol conformance lookups of concrete types
anyway---create it with a LookupConformanceFn. This is NFC for now,
but moves us closer to making archetype builders more canonicalizable
and reusable.
Teach the serialized form of ArchetypeType about its owning generic
environment, so we can wire up the generic environment of (primary)
archetypes eagerly (at the point of deserialization) rather than when
we form the generic environment. This ensures that there is no point
at which we have a (non-opened-existential) archetype without a
generic environment.
... except that the type reconstruction code creates such archetypes.
Fixes assertion failures in SILGen and the optimizer with this
exotic setup:
protocol P {
associatedtype T : Q
}
protocol Q {
func requirement<U : P>(u: U) where U.T == Self
}
Here, we only have a U : P conformance, and not Self : Q,
because Self : Q is available as U.T : Q.
There were three problems here:
- The SIL verifier was too strict in verifying the generic signature.
All that matters is we can get the Self parameter conformance, not
that it's the first requirement, etc.
- GenericSignature::getSubstitutionMap() had a TODO concerning handling
of same-type constraints -- this is the first test-case I've found
that triggered the problem.
- GenericEnvironment::getSubstitutionMap() incorrectly ignored
same-type constraints where one of the two types was a generic
parameter.
Fixes <https://bugs.swift.org/browse/SR-3321>.
- The DeclContext versions of these methods have equivalents
on the DeclContext class; use them instead.
- The GenericEnvironment versions of these methods are now
static methods on the GenericEnvironment class. Note that
these are not made redundant by the instance methods on
GenericEnvironment, since the static methods can also be
called with a null GenericEnvironment, in which case they
just assert that the type is fully concrete.
- Remove some unnecessary #includes of ArchetypeBuilder.h
and GenericEnvironment.h. Now changes to these files
result in a lot less recompilation.
Serialize generic environments via a generic environment ID with a
separte offset table, so we have identity for the generic environments
and will share generic environments on deserialization.
The substitution only replaces archetypes with abstract generic parameters, so no conformance lookup is necessary, and we can provide a "lookup" callback now that just vends abstract conformances.
(Ideally, we'd be able to do this for mapTypeIntoContext too, but we run into problems with generic signatures with same-type constraints on associated types with protocol requirements. Mapping `t_0_0.AssocType` into such a context will require conformance lookup for the concrete type replacement, since same-type Requirements don't preserve the conformances that satisfy the protocol requirements for the same-type relationship.)
This is a more flexible interface that allows substitution operations to avoid needing an eager SubstitutionMap without relying on module-based conformance lookup. NFC yet.
While not strictly needed for type checking, it's extremely useful for
debugging and verification to know what context a particular generic
environment is associated with. This information was in a kludgy side
table, but it's worth a pointer in GenericEnvironment to always have
it available.
We no longer need a separate "pass" that creates an archetype builder
that inherits context archetypes, because we no longer ever inherit
context archetypes.
Store the archetype-to-interface-type mapping (which is used to map
*out* of a generic environment) is a tail-allocated array of
(archetype, generic type parameter) pairs. This array is built up
lazily, as we compute the context types for generic parameters.
Searching in this array is linear while it is being constructed. Once
it is complete, it is sorted so that future searches are logarithmic.
Aside from the space savings of not having a DenseMap lying around,
this means we no longer need to register a destructor of a
GenericEnvironment with the ASTContext, which saves us tear-down
time.
Teach GenericEnvironment to lazily populate its mapping from generic
parameters to context types when queried (e.g., during
substitutition) rather than assuming that will be pre-populated before
any queries occur.
We're still forcing all of the archetypes when the generic environment
is created by the archetype builder; baby steps!
Rather than storing a heavyweight DenseMap for the mapping from
interface types (which are always generic type parameters) to their
corresponding context types, tail-allocate the array of context types
as an array parallel to the generic type parameters array. Use
GenericParamKey's lookup facilities and the new
type-substitution-function-based version of Type::subst() to handle
queries efficiently.
The "core" data structure used to record the substitutions to be
performed is a TypeSubstitutionMap, which is a DenseMap. This is a
fairly heavyweight, static data structure for something where
* We occasionally want a more dynamic, lazily-populated data structure, and
* We can usually provide more efficient storage than a DenseMap.
So, introduce a Type::subst() variant that takes a TypeSubstitutionFn,
which is just a function that maps a SubstitutableType * to a Type (or
nothing). Use this as the core variant of subst(). with an adapter for
existing TypeSubstitutionMaps. Over time, TypeSubstitutionMap should
go away.
This eliminates the really gross registration of archetype builders
within the ASTContext, and is another little step toward lazily
constructing archetypes.
The root potential archetypes in an archetype builder are associated
with generic parameters. Start decoupling potential archetypes from a
specific GenericTypeParamType and instead work with the abstracted
depth/index. The goal here is to allow the same archetype builder to
be used within different generic environments (which includes both
different generic parameters and different archetypes).
As part of this, boost the archetype builder's GenericTypeParamKey
from a local type to a more generic GenericParamKey that can be used
in other interfaces that want to work with abstracted generic
parameters.
Stop recording specific archetypes anywhere in
PotentialArchetype. Instead, use a GenericEnvironment to record/query
the archetype that corresponds to that PotentialArchetype, making it
possible to use the same archetype builder (and its potential
archetypes) to build multiple generic environments.
GenericEnvironment walked its input mapping in DenseMap order while
populating a reverse mapping from archetypes to interface
types. However, this mapping is not unique, because two generic
parameters can end up mapping to the same archetype. In such cases,
which generic parameter we mapped to was nondeterministic.
Make this deterministic by preferring to map back to the earlier
generic parameter.
ASTContext-allocated objects don't get destructed unless they are
registered; make sure to do that for GenericEnvironments, because
we're leaking them like crazy.
Type substitution works on a fairly narrow set of types: generic type
parameters (to, e.g., use a generic) and archetypes (to map out of a
generic context). Historically, it was also used with
DependentMemberTypes, but recent refactoring to eliminate witness
markers eliminate that code path.
Therefore, narrow TypeSubstitutionMap's keys to SubstitutableType,
which covers archetypes and generic type parameters. NFC
An environment is always associated with a location with a signature, so
having them separate is pointless duplication. This patch also updates
the serialization to round-trip the signature data.
