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.
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.
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.
Rather than directly using the ArchetypeBuilder associated with a
canonical generic signature, use a canonical GenericEnvironment
associated with that canonical generic signature. This has a few
benefits:
* It's cleaner to not have IRGen working with archetype builders;
GenericEnvironment is the right abstraction for mapping between
dependent types and archetypes for a specific context.
* It helps us separate the archetype builder from a *specific*
set of archetypes. This is an ongoing refactor that is intended to
allow us to re-use archetype builders across different generic
environments.
As part of this, ArchetypeBuilder::substDependentType() has gone away
in favor of GenericEnvironment::mapTypeIntoContext().
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.
Sugared GenericTypeParamTypes point to GenericTypeParamDecls,
allowing the name of the parameter as written by the user to be
recovered. Canonical GenericTypeParamTypes on the other hand
only store a depth and index, without referencing the original
declaration.
When printing SIL, we wish to output the original generic parameter
names, even though SIL only uses canonical types. Previously,
we used to accomplish this by mapping the generic parameter to an
archetype and printing the name of the archetype. This was not
adequate if multiple generic parameters mapped to the same
archetype, or if a generic parameter was mapped to a concrete type.
The new approach preserves the original sugared types in the
GenericEnvironment, adding a new GenericEnvironment::getSugaredType()
method.
There are also some other assorted simplifications made possible
by this.
Unfortunately this makes GenericEnvironments use a bit more memory,
however I have more improvements coming that will offset the gains,
in addition to making substitution lists smaller also.
There's a bit of a hack to deal with generic typealiases, but
overall this makes things more logical.
This is the last big refactoring before we can allow constrained
extensions to make generic parameters concrete. All that remains
is a small set of changes to SIL type lowering, and retooling
some diagnostics in Sema.
This patch is rather large, since it was hard to make this change
incrementally, but most of the changes are mechanical.
Now that we have a lighter-weight data structure in the AST for mapping
interface types to archetypes and vice versa, use that in SIL instead of
a GenericParamList.
This means that when serializing a SILFunction body, we no longer need to
serialize references to archetypes from other modules.
Several methods used for forming substitutions can now be moved from
GenericParamList to GenericEnvironment.
Also, GenericParamList::cloneWithOuterParameters() and
GenericParamList::getEmpty() can now go away, since they were only used
when SILGen-ing witness thunks.
Finally, when printing generic parameters with identical names, the
SIL printer used to number them from highest depth to lowest, by
walking generic parameter lists starting with the innermost one.
Now, ambiguous generic parameters are numbered from lowest depth
to highest, by walking the generic signature, which means test
output in one of the SILGen tests has changed.
A GenericEnvironment stores the mapping between GenericTypeParamTypes
and context archetypes (or eventually, concrete types, once we allow
extensions to constrain a generic parameter to a concrete type).
The goals here are two-fold:
- Eliminate the GenericTypeParamDecl::getArchetype() method, and
always use mapTypeIntoContext() instead
- Replace SILFunction::ContextGenericParams with a GenericEnvironment
This patch adds the new data type as well as serializer and AST
verifier support. but nothing else uses it yet.
Note that GenericSignature::get() now asserts if there are no
generic parameters, instead of returning null. This requires a
few tweaks here and there.
