It's better to ask SILType if it is MoveOnly than go to the AST type and
ask if it is noncopyable, because some types in SIL do not have a
well-defined notion of conformance in the AST.
A FunctionTest created in Swift source has no persistent storage
address. This results in sporadic crashes when running unit tests.
Fix the FunctionTest registry to store the value of the test.
Eventually, we could probably rig something up with @_rawLayout, but
it makes more sense for FunctionTest to be a value type anyway.
Even if the final pattern ends up consuming the value, the match itself
must be nondestructive, because any match condition could fail and cause
us to have to go back to the original aggregate. For copyable values,
we can always copy our way out of consuming operations, but we don't
have that luxury for noncopyable types, so the entire match operation
has to be done as a borrow.
For address-only enums, this requires codifying part of our tag layout
algorithm in SIL, namely that an address-only enum will never use
spare bits or other overlapping storage for the enum tag. This allows
us to assume that `unchecked_take_enum_data_addr` is safely non-side-
effecting and match an address-only noncopyable enum as a borrow.
I put TODOs to remove defensive copies from various parts of our
copyable enum codegen, as well as to have the instruction report
its memory behavior as `None` when the projection is nondestructive,
but this disturbs SILGen for existing code in ways SIL passes aren't
yet ready for, so I'll leave those as is for now.
This patch is enough to get simple examples of noncopyable enum switches
to SILGen correctly. Additional work is necessary to stage in the binding
step of the pattern match; for a consuming switch, we'll need to end
the borrow(s) and then reproject the matched components so we can
consume them moving them into the owned bindings. The move-only checker
also needs to be updated because it currently always tries to convert
a switch into a consuming operation.
The specific semantics is if we assign into a transferring parameter's field,
then we "merge" src's value into the transferring parameter, so we
conservatively leave the region of the transferring parameter alone. If we
assign over the entire transferring parameter, we perform an assign fresh since
any value that used to be in the transferring parameter cannot reference
anything in its new value since they are all gone.
NOTE: This does not handle yet assignment into transferring parameters. In the
next commit, I am going to teach the checker that assigning into such a
parameter is a transfer.
When the BitwiseCopyable experimental feature is enabled, infer types to
conform to `_BitwiseCopyable`. The `_BitwiseCopyable` inference broadly
follows the approach taken to infer `Sendable`.
(1) Special types are conformed:
- function types if trivial
- metatypes
- builtin types if trivial
(2) TheTupleType is conditionally conformed.
(3) Nominal types are conformed if:
- non-public or public+fixed-layout
- enum or struct (non-class)
- every field conforms to _BitwiseCopyable
Additionally, check that nominal types which are explicitly conformed to
`_BitwiseCopyable` satisfy the latter two conditions of (3).
For a public, non-fixed-layout type to conform to `_BitwiseCopyable`,
the user must conform the type explicitly.
Finally, verify that conformances correspond to TypeLowering's notion of
triviality to the appropriate extent:
- if a type isn't trivial, it doesn't conform to `_BitwiseCopyable`
unless it's an archetype
- if a type is trivial, it conforms to `_BitwiseCopyable` unless some
field in its layout doesn't conform to `_BitwiseCopyable`, which is
only permitted under certain circumstances (the type has generic
parameters, the type is public non-fixed-layout, the type is a
reference but has ReferenceStorage::Unmanaged, the type is a
ModuleType, etc.)
Optionally, the dependency to the initialization of the global can be specified with a dependency token `depends_on <token>`.
This is usually a `builtin "once"` which calls the initializer for the global variable.
The instruction exists to express the atomic initialization of a
tuple-typed address in address-lowered mode. In opaque-values mode,
this is expressed as an assign/store.
The dependent 'value' may be marked 'nonescaping', which guarantees that the
lifetime dependence is statically enforceable. In this case, the compiler
must be able to follow all values forwarded from the dependent 'value', and
recognize all final (non-forwarded, non-escaping) use points. This implies
that `findPointerEscape` is false. A diagnostic pass checks that the
incoming SIL to verify that these use points are all initially within the
'base' lifetime. Regular 'mark_dependence' semantics ensure that
optimizations cannot violate the lifetime dependence after diagnostics.
Previously, mayRequirePackMetadata only considered whether a type
involved a pack. That failed to account for the case of outlined value
functions that require pack metadata when the type involves a pack in
its layout. Here, mayRequirePackMetadata now considers also whether the
layout corresponding to a type involves a pack.
rdar://119829826
Layers:
- FunctionConvention: AST FunctionType: results, parameters
- ArgumentConventions: SIL function arguments
- ApplyOperandConventions: applied operands
The meaning of an integer index is determined by the collection
type. All the mapping between the various indices (results,
parameters, SIL argument, applied arguments) is restricted to the
collection type that owns that mapping. Remove the concept of a
"caller argument index".
