When generating dead stub methods for vtable entries, we should not
attach COMDATs to their definitions. This is because such stubs may be
referenced only through aliases, and the presence of a COMDAT on the
stub definition would cause the aliased symbol, we want to keep, to be
discarded from the symbol table when other object files also have a
dead stub method.
Given the following two object files generated:
```mermaid
graph TD
subgraph O0[A.swift.o]
subgraph C0[COMDAT Group swift_dead_method_stub]
D0_0["[Def] swift_dead_method_stub"]
end
S0_0["[Symbol] swift_dead_method_stub"] --> D0_0
S1["[Symbol] C1.dead"] --alias--> D0_0
end
subgraph O1[B.swift.o]
subgraph C1[COMDAT Group swift_dead_method_stub]
D0_1["[Def] swift_dead_method_stub"]
end
S0_1["[Symbol] swift_dead_method_stub"] --> D0_1
S2["[Symbol] C2.beef"] --alias--> D0_1
end
```
When linking these two object files, the linker will pick one of the
COMDAT groups of `swift_dead_method_stub`. The other COMDAT group will be
discarded, along with all symbols aliased to the discarded definition,
even though those aliased symbols (`C1.dead` and `C2.beef`) are the
ones we want to keep to construct vtables.
This change stops attaching COMDATs to dead stub method definitions.
This effectively only affects WebAssembly targets because MachO's
`supportsCOMDAT` returns false, and COFF targets don't use
`linkonce_odr` for dead stub methods.
The COMDAT was added in 7e8f782457
Removes the underscored prefixes from the @_section and @_used attributes, making them public as @section and @used respectively. The SymbolLinkageMarkers experimental feature has been removed as these attributes are now part of the standard language. Implemented expression syntactic checking rules per SE-0492.
Major parts:
- Renamed @_section to @section and @_used to @used
- Removed the SymbolLinkageMarkers experimental feature
- Added parsing support for the old underscored names with deprecation warnings
- Updated all tests and examples to use the new attribute names
- Added syntactic validation for @section to align with SE-0492 (reusing the legality checker by @artemcm)
- Changed @DebugDescription macro to explicitly use a tuple type instead of type inferring it, to comply with the expression syntax rules
- Added a testcase for the various allowed and disallowed syntactic forms, `test/ConstValues/SectionSyntactic.swift`.
When Embedded Swift emits a symbol that was imported from another
module, ensure that the symbol is emitted as a weak definition. This
way, importing the same module (and using its symbol) into several
different modules doesn't cause duplicate-symbol errors at link time.
Rather, the linker will merge the different symbol definitions. This
makes Embedded Swift libraries work without resorting to
`-mergeable-symbols` or `-emit-empty-object-file`.
If `LinkEntity::isTypeKind()` is true, `IRGenModule::getAddrOfLLVMVariable` assumes that we can safely call
`LinkEntity::getType()`, which does `reinterpret_cast` of `LinkEntity::Pointer` to `TypeBase *`. However, for SIL
differentiability witness, the pointer has `SILDifferentiabilityWitness *` type, which is not derived from `TypeBase`. So, such a cast is not allowed.
Just as with `ProtocolWitnessTableLazyAccessFunction` and `ProtocolWitnessTableLazyCacheVariable` link entity kinds (which are also type kinds), we should use `SecondaryPointer` instead of `Pointer` for storing payload here, while setting `Pointer` to `nullptr`.
Key paths can't reference non-escapable or non-copyable storage declarations,
so we don't need to refer to them resiliently, and can elide their property
descriptors.
However, declarations may still be conditionally Copyable and Escapable, and
if so, then they still need a property descriptor for resilient key path
references. When a property or subscript can be used in a context where it
is fully Copyable and Escapable, emit the property descriptor in a generic
environment constrained by the necessary conditional constraints.
Fixes rdar://151628396.
There are numerous entity kinds declared after
`ProtocolWitnessTableLazyAccessFunction` which aren't type kinds. Group
all those which are type kinds together for now. In the fullness of
time it would probably we wise to replace this implementation with a
switch statement so that when new kinds are added there is a chance that
the type-ness of that kind can be considered.
The well known builtin and structural types are strongly defined in the
runtime which is compacted into the standard library. Given that the VWT
is defined in the runtime, it is not visible to the Swift compilation
process and as we do not provide a Swift definition, we would previously
compute the linkage as being module external (`dllimport` for shared
library builds). This formed incorrect references to these variables and
would require thunking to adjust the references.
One special case that we add here is the "any function" type
representation (`@escaping () -> ()`) as we do use the VWT for this type
in the standard library but do not consider it part of the well known
builtin or structural type enumeration.
These errors were previously being swallowed by the build system and
thus escaped from being fixed when the other cases of incorrect DLL
storage were.
Property descriptors for static properties were only recently introduced with
SE-438. Since these symbols are not present in Swift libraries that were
compiled with earlier versions of the compiler, it is not safe for
`#_hasSymbol` to check for the property descriptor symbols, since they can be
absent at either link time or runtime.
Resolves rdar://139749275.
The main change here is to associate a witness table with a `ProtocolConformance` instead of a `RootProtocolConformance`.
A `ProtocolConformance` is the base class and can be a `RootProtocolConformance` or a `SpecializedProtocolConformance`.
Motivated by need for protocol-based dynamic dispatch, which hasn't been possible in Embedded Swift due to a full ban on existentials. This lifts that restriction but only for class-bound existentials: Class-bound existentials are already (even in desktop Swift) much more lightweight than full existentials, as they don't need type metadata, their containers are typically 2 words only (reference + wtable pointer), don't incur copies (only retains+releases).
Included in this PR:
[x] Non-generic class-bound existentials, executable tests for those.
[x] Extension methods on protocols and using those from a class-bound existential.
[x] RuntimeEffects now differentiate between Existential and ExistentialClassBound.
[x] PerformanceDiagnostics don't flag ExistentialClassBound in Embedded Swift.
[x] WTables are generated in IRGen when needed.
Left for follow-up PRs:
[ ] Generic classes support
The generality of the `AvailabilityContext` name made it seem like it
encapsulates more than it does. Really it just augments `VersionRange` with
additional set algebra operations that are useful for availability
computations. The `AvailabilityContext` name should be reserved for something
pulls together more than just a single version.
- VTableSpecializer, a new pass that synthesizes a new vtable per each observed concrete type used
- Don't use full type metadata refs in embedded Swift
- Lazily emit specialized class metadata (LazySpecializedClassMetadata) in IRGen
- Don't emit regular class metadata for a class decl if it's generic (only emit the specialized metadata)
- In embedded Swift, classes get a simplified metadata: Basically just a vtable + destructor + superclass pointer.
- Only non-resilient (intended as permanent restriction), non-generic classes (for now) supported.
- Relax the check that prohibits metadata emission and usage to allow classes.
Partially address the incorrect handling for the `#dsohandle` on
Windows.
We were previously emitting a local definition for this external
constant, and worse yet, not marking the definition for COMDAT. It is
unclear what definition would win ultimately (implementation defined),
as we had a definition as well as the linker synthesized value. We can
change the SIL linkage for this type to `DefaultForDeclaration` which
will give it `available_externally` and default visibility and storage
which is closer to what we desire. However, because we do not track the
LLVM variables and apply heuristics for lowering the
`SILGlobalVariable`, we would attribute it with imported DLL Storage.
This would then cause us to fail at link time (amusingly enough link.exe
will report a LNK1000). Special case the variable and track that we are
targeting a windows environment in the `UniversalLinkageInfo` so that we
do not special case this on other platforms.
This also has the nice side effect of allowing us to remove the special
case in the TBD handling.
Fixes: #64741
For each decl that needs a `#_hasSymbol()` query function, emit the corresponding helper function body during IRGen. Use `IRSymbolVisitor` to collect linkable symbols associated with the decl and return true from the helper function if the address of every associated symbol is non-null.
Resolves rdar://101884587
This commit begins to generate correct metadata for @_objcImplementation extensions:
• Swift-specific metadata and symbols are not generated.
• For main-class @_objcImpls, we visit the class to emit metadata, but visit the extension’s members.
• Includes both IR tests and executable tests, including coverage of same-module @objc subclasses, different-module @objc subclasses, and clang subclasses.
The test cases do not yet cover stored properties.
So far, static arrays had to be put into a writable section, because the isa pointer and the (immortal) ref count field were initialized dynamically at the first use of such an array.
But with a new runtime library, which exports the symbols for the (immortal) ref count field and the isa pointer, it's possible to put the whole array into a read-only section. I.e. make it a constant global.
rdar://94185998
This reverts the revert commit df353ff3c0.
Also, I added a frontend option to disable this optimization: `-disable-readonly-static-objects`
So far, static arrays had to be put into a writable section, because the isa pointer and the (immortal) ref count field were initialized dynamically at the first use of such an array.
But with a new runtime library, which exports the symbols for the (immortal) ref count field and the isa pointer, it's possible to put the whole array into a read-only section. I.e. make it a constant global.
rdar://94185998
I wrote out this whole analysis of why different existential types
might have the same logical content, and then I turned around and
immediately uniqued existential shapes purely by logical content
rather than the (generalized) formal type. Oh well. At least it's
not too late to make ABI changes like this.
We now store a reference to a mangling of the generalized formal
type directly in the shape. This type alone is sufficient to unique
the shape:
- By the nature of the generalization algorithm, every type parameter
in the generalization signature should be mentioned in the
generalized formal type in a deterministic order.
- By the nature of the generalization algorithm, every other
requirement in the generalization signature should be implied
by the positions in which generalization type parameters appear
(e.g. because the formal type is C<T> & P, where C constrains
its type parameter for well-formedness).
- The requirement signature and type expression are extracted from
the existential type.
As a result, we no longer rely on computing a unique hash at
compile time.
Storing this separately from the requirement signature potentially
allows runtimes with general shape support to work with future
extensions to existential types even if they cannot demangle the
generalized formal type.
Storing the generalized formal type also allows us to easily and
reliably extract the formal type of the existential. Otherwise,
it's quite a heroic endeavor to match requirements back up with
primary associated types. Doing so would also only allows us to
extract *some* matching formal type, not necessarily the *right*
formal type. So there's some good synergy here.
This pipes the `-static` flag when building a static library into IRGen.
This should have no impact on non-Windows targets as the usage of the
information simply removes the `dllexport` attribute on the generated
interfaces. This ensures that a library built with `-static` will not
re-export its interfaces from the consumer. This is important to ensure
that the consumer does not vend the API surface when it statically links
a library. In conjunction with the removal of the force load symbol,
this allows the generation of static libraries which may be linked
against on Windows. However, a subsequent change is needed to ensure
that the consumer does not mark the symbol as being imported from a
foreign module (i.e. `dllimport`).
