Specialize #1725
Merged
Specialize #1725
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
@swift-ci Please test |
|
👍 |
| @@ -713,6 +713,35 @@ the virtual dispatch, inline calls when appropriate, and eliminate the overhead | |||
| of the generic system. Such optimizations can be performed based on heuristics, | |||
| user direction, or profile-guided optimization. | |||
|
|
|||
| An internal @_specialize function attribute allows devlopers to force | |||
This attribute can be attached to generic functions. The attribute's
arguments must be a list of concrete types to be substituted in the
function's generic signature. Any number of specializations may be
associated with a generic function.
This attribute provides a hint to the compiler. At -O, the compiler
will generate the specified specializations and emit calls to the
specialized code in the original generic function guarded by type
checks.
The current attribute is designed to be an internal tool for
performance experimentation. It does not affect the language or
API. This work may be extended in the future to add user-visible
attributes that do provide API guarantees and/or direct dispatch to
specialized code.
This attribute works on any generic function: a freestanding function
with generic type parameters, a nongeneric method declared in a
generic class, a generic method in a nongeneric class or a generic
method in a generic class. A function's generic signature is a
concatenation of the generic context and the function's own generic
type parameters.
e.g.
struct S<T> {
var x: T
@_specialize(Int, Float)
mutating func exchangeSecond<U>(u: U, _ t: T) -> (U, T) {
x = t
return (u, x)
}
}
// Substitutes: <T, U> with <Int, Float> producing:
// S<Int>::exchangeSecond<Float>(u: Float, t: Int) -> (Float, Int)
|
@atrick Are you planning to add a benchmark for this feature? I think it would make a lot of sense. And, BTW, does this feature generate specializations even at |
|
@swiftix Yes, I'm planning to add benchmarks. The one that I have is nontrivial to integrate because it involves modules. I did not tie any of the test cases to the -O or -Onone pipeline. The pass currently runs at -O and I don't have any plans to change -Onone. |
|
@swift-ci Please test |
This pass finds generic functions with @_specialized attributes and generates specialized code for the attribute's concrete types. It inserts type checks and guarded dispatch at the beginning of the generic function for each specialization. Since we don't currently expose this attribute as API and don't specialize vtables and witness tables yet, the only way to reach the specialized code is by calling the generic function which performs the guarded dispatch. In the future, we can build on this work in several ways: - cross module dispatch directly to specialized code - dynamic dispatch directly to specialized code - automated specialization based on less specific hints - partial specialization - and so on... I reorganized and refactored the optimizer's generic utilities to support direct function specialization as opposed to apply specialization.
|
@swift-ci Please test |
atrick
added a commit
that referenced
this pull request
Mar 22, 2016
Reapply "Merge pull request #1725 from atrick/specialize"
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Introduces an @_specialize(...) function attribute.
An internal @_specialize function attribute allows developers to force
full specialization by listing concrete type names corresponding to the
function's generic signature. A function's generic signature is a
concatenation of its generic context and the function's own generic
type parameters.
@_specialize currently acts as a hint to the optimizer, which
generates type checks and code to dispatch to the specialized routine
without affecting the signature of the generic function. The
intention is to support efforts at evaluating the performance of
specialized code. The performance impact is not guaranteed and is
likely to change with the optimizer. This attribute should only be
used in conjunction with rigorous performance analysis. Eventually,
a similar attribute could be defined in the language, allowing it to be
exposed as part of a function's API. That would allow direct dispatch
to specialized code without type checks, even across modules.
In the future, we can build on this work in several ways:
@swift-ci Please test