mirror of
https://github.com/apple/swift.git
synced 2026-06-20 15:42:51 +02:00
Doug Gregor
f2eb7cb1a8
The `@export(interface)` and `@export(implementation)` attributes SE-0497 are queried directly on AST nodes in several places within the SIL pipeline. However, they don't persist when SIL functions are serialized, meaning that clients of the original module might make different assumptions about the availability of a given function's definition. Represent these attributes in a SIL function (as an optional CodeGenerationModel), (de-)serialize them into the module, and add a textual representation as SIL function attributes `[export_interface]` and `[export_implementation]`.
252 lines
6.6 KiB
Markdown
252 lines
6.6 KiB
Markdown
# Function Attributes
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This document is a reference guide for SIL function attributes. For an overview
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of SIL and OSSA see the [SIL](SIL.md) document.
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### Canonical SIL stage override
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```
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sil-function-attribute ::= '[canonical]'
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```
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The function is in canonical SIL even if the module is still in raw SIL.
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### Ownership SSA
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```
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sil-function-attribute ::= '[ossa]'
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```
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The function is in OSSA (ownership SSA) form.
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### Transparent functions
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```
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sil-function-attribute ::= '[transparent]'
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```
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Transparent functions are always inlined and don't keep their source
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information when inlined.
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### Thunks
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```
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sil-function-attribute ::= '[' sil-function-thunk ']'
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sil-function-thunk ::= 'thunk'
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sil-function-thunk ::= 'signature_optimized_thunk'
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sil-function-thunk ::= 'reabstraction_thunk'
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sil-function-thunk ::= 'back_deployed_thunk'
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```
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The function is a compiler generated thunk.
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```
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sil-function-attribute ::= '[without_actually_escaping]'
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```
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The function is a thunk for closures which are not actually escaping.
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### Dynamically replaceable functions
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```
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sil-function-attribute ::= '[dynamically_replacable]'
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```
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The function can be replaced at runtime with a different implementation.
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Optimizations must not assume anything about such a function, even if
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the SIL of the function body is available.
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```
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sil-function-attribute ::= '[dynamic_replacement_for' identifier ']'
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sil-function-attribute ::= '[objc_replacement_for' identifier ']'
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```
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Specifies for which function this function is a replacement.
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### exact_self_class
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```
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sil-function-attribute ::= '[exact_self_class]'
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```
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The function is a designated initializers, where it is known that the
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static type being allocated is the type of the class that defines the
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designated initializer.
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### Global variable initialization
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```
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sil-function-attribute ::= '[' sil-function-purpose ']'
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sil-function-purpose ::= 'global_init'
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```
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A `global_init` function is used to access a global variable which needs to be
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initialized the first time the accessor is called. The implied semantics of a
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`global_init` function are:
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- side-effects can occur any time before the first invocation.
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- all calls to the same `global_init` function have the same
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side-effects.
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- any operation that may observe the initializer's side-effects
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must be preceded by a call to the initializer.
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This is currently true if the function is an addressor that was lazily
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generated from a global variable access. Note that the initialization
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function itself does not need this attribute. It is private and only
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called within the addressor.
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```
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sil-function-purpose ::= 'global_init_once_fn'
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```
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The actual initialization function for a global, which is called once by its
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corresponding `global_init` function.
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```
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sil-function-purpose ::= 'lazy_getter'
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```
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The function is a getter of a lazy property for which the backing storage is an
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`Optional` of the property's type. The getter contains a top-level
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[`switch_enum`](Instructions.md#switch_enum) (or
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[`switch_enum_addr`](Instructions.md#switch_enum_addr)), which tests if the
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lazy property is already computed. In the `None`-case, the property is computed
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and stored to the backing storage of the property.
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After the first call of a lazy property getter, it is guaranteed that
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the property is computed and consecutive calls always execute the
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`Some`-case of the top-level [`switch_enum`](Instructions.md#switch_enum).
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### Weakly imported functions
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```
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sil-function-attribute ::= '[weak_imported]'
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```
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Cross-module references to this function should always use weak linking.
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### Export of of the function body
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```
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sil-function-attribute ::= '[export_interface]'
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sil-function-attribute ::= '[export_implementation]'
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```
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SIL representation of the `@export(interface)` and `@export(implementation)`
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attributes, respectively. The former implies that the function body is never
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serialized to be made available to clients of the module. The latter implies
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that the function body is always serialized, and clients must emit a (shared)
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copy of it if they need to use the function.
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### Stack protection
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```
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sil-function-attribute ::= '[stack_protection]'
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```
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Stack protectors are inserted into this function to detect stack related
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buffer overflows.
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### Availability
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```
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sil-function-attribute ::= '[available' sil-version-tuple ']'
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sil-version-tuple ::= [0-9]+ ('.' [0-9]+)*
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```
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The minimal OS-version where the function is available.
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### Function inlining control
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```
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sil-function-attribute ::= '[' sil-function-inlining ']'
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sil-function-inlining ::= 'noinline'
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```
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The function is never inlined.
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```
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sil-function-inlining ::= 'always_inline'
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```
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The function is always inlined.
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### Optimization modes
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```
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sil-function-attribute ::= '[' sil-function-optimization ']'
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sil-function-inlining ::= 'Onone'
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sil-function-inlining ::= 'Ospeed'
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sil-function-inlining ::= 'Osize'
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```
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The function is optimized according to this attribute, overriding the
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setting from the command line.
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```
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sil-function-attribute ::= '[' sil-function-effects ']'
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sil-function-effects ::= 'readonly'
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sil-function-effects ::= 'readnone'
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sil-function-effects ::= 'readwrite'
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sil-function-effects ::= 'releasenone'
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```
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The specified memory effects of the function.
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### Semantic attributes
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```
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sil-function-attribute ::= '[_semantics "' [A-Za-z._0-9]+ '"]'
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```
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The specified high-level semantics of the function. The optimizer can
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use this information to perform high-level optimizations before such
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functions are inlined. For example, `Array` operations are annotated
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with semantic attributes to let the optimizer perform redundant bounds
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check elimination and similar optimizations.
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### Pre-specialization
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```
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sil-function-attribute ::= '[_specialize "' [A-Za-z._0-9]+ '"]'
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```
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Specifies for which types specialized code should be generated.
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### Clang node owner
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```
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sil-function-attribute ::= '[clang "' identifier '"]'
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```
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The clang node owner.
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### Performance constraints
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```
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sil-function-attribute ::= '[' performance-constraint ']'
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performance-constraint :: 'no_locks'
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performance-constraint :: 'no_allocation'
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```
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Specifies the performance constraints for the function, which defines
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which type of runtime functions are allowed to be called from the
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function.
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```
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sil-function-attribute ::= '[perf_constraint]'
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```
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Specifies that the optimizer and IRGen must not add runtime calls which
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are not in the function originally. This attribute is set for functions
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with performance constraints or functions which are called from
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functions with performance constraints.
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### Naming
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```
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sil-function-attribute :: '[' asmname "' identifier '" ']'
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```
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Specifies that the SIL function should be lowered to LLVM IR with the given function name.
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