Fixed-ABI means that we can do value operations on the type without
any metadata: value-allocations, copies, and destroys. It's currently
equivalent to being fixed-size, but (1) being fixed-size isn't useful
by itself at the SIL level and (2) you can imagine resilience or generics
micro-optimizations where there's like an attribute that tells us the
size of a type without actually telling us how to copy it. All types
are fixed-ABI except:
- layout-unconstrained generic types,
- resilient value types, and
- value types which contain a subobject of such a type (except within
indirect enum cases).
ABI-accessible means that we can perform value operations at all.
We might not be able to if the type is not fixed-ABI and it is private
to a different file (in non-WMO builds) or internal to a different
module, because in such cases we will not be able to access its metadata.
In general, we can't use such types `T` directly, but we may be able to
use types `C` that contain such types as subobjects. Furthermore, we
may be reasonably exposed to SIL that performs operations that treat `C`
as non-opaque, e.g. if `C` is frozen (as it will be by default for
modules in Swift 5). We can still achieve correctness in these cases
as long as we don't either:
- inline code that contains value operations on `T` or
- attempt to recursively expand a value operation on `T` into value
operations on its subobjects.
The SIL optimizer currently never tries to expand value operations on
objects in memory. However, IRGen always recursively expands value
operations on frozen types; that will be fixed in a follow-up patch.
The SIL verification that I've added here is definitely incomplete.
For large basic blocks the dominance check between two instructions in the same block was very expensive.
Although the verifier does not run in no-assert compiler builds, we don't want it to be extra slow for assert builds.
https://bugs.swift.org/browse/SR-7632
Mandatory pass will clean it up and replace it by a copy_block and
is_escaping/cond_fail/release combination on the %closure in follow-up
patches.
The instruction marks the dependence of a block on a closure that is
used as an 'withoutActuallyEscaping' sentinel.
rdar://39682865
- Fix some type system issues with looking up member types in/out of context.
- Correctly upcast a class-constrained existential or archetype to the base class when referencing a base class field on a generic type.
Fixes SR-7106 | rdar://problem/38070998.
A public subscript might have generic indexes that aren't unconditionally Hashable, or might use indexes that are retroactively made Hashable, so the property descriptor on the implementer's side can't always resiliently provide this information to the final instantiated KeyPath.
