First prototype of Performance Annotations #39902
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mikeash
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Oct 25, 2021
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Really cool stuff. I did not look closely at all of the effects annotations on the runtime functions to make sure they're correct. Let me know if and when you'd like me to do that. I figured we might at least want to wait until you're farther along before we put in that effort.
| ERROR(performance_arc,none, | ||
| "this code performs reference counting operations which can cause locking", ()) | ||
| ERROR(performance_objectivec,none, | ||
| "calls of Objective-C methods can have unpredictable performance", ()) |
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objc_msgSend will also take a lock on the slow path, and the slow path can happen unpredictably due to cache invalidation. Not sure if that's also worth calling out.
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I think "unpredictable performance" is a strong enough term which IMO includes locks, etc.
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| // Class objc_lookUpClass(const char *name); | ||
| FUNCTION(LookUpClass, objc_lookUpClass, C_CC, AlwaysAvailable, | ||
| RETURNS(ObjCClassPtrTy), | ||
| ARGS(Int8PtrTy), | ||
| ATTRS(NoUnwind, ReadNone)) | ||
| ATTRS(NoUnwind, ReadNone), | ||
| EFFECT(MetaData)) |
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Wow, adding all of these effects annotations was a big job.
JensAyton
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Oct 27, 2021
include/swift/AST/DiagnosticsSIL.def
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| @@ -311,6 +311,34 @@ WARNING(warn_dead_weak_store,none, | |||
| "weak reference will always be nil because the referenced object is " | |||
| "deallocated here", ()) | |||
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| // performance diagnostics | |||
| ERROR(performance_annotations_not_enabled,none, | |||
| "use -experimental-performance-annotations to enabled performance annotations", ()) | |||
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looks pretty good |
…to enable performance annotations
Define the possible runtime effects of an instruction in an enum `RuntimeEffect`. Add a new utility `swift:getRuntimeEffect` to estimate the runtime effects of an instruction. Also, add a mechanism to validate the correctness of the analysis in IRGen: annotate all runtime functions in RuntimeFunctions.def with the actual effect what the runtime function has or can have. Then check if the effects of emitted runtime functions for an instruction match what `getRuntimeEffect` predicts. This check is only enabled on demand by defining the CHECK_RUNTIME_EFFECT_ANALYSIS macro in RuntimeEffect.h
…rrorHandlingBlocks * ReachingReturnBlocks: computes the set of blocks from which a path to the return-block exists (does not include paths to a throw-block) * NonErrorHandlingBlocks: computes the set of blocks which are not used for error handling, i.e. not (exclusively) reachable from the error-block of a try_apply
…s into a separate utility.
… into stand-alone utility functions
This pass is only used for functions with performance annotations (@_noLocks, @_noAllocation). It runs in the mandatory pipeline and specializes all function calls in performance-annotated functions and functions which are called from such functions. In addition, the pass also does some other related optimizations: devirtualization, constant-folding Builtin.canBeClass, inlining of transparent functions and memory access optimizations.
…iagnostics in the passed closure.
…ions in annotated functions. The PerformanceDiagnostics pass issues performance diagnostics for functions which are annotated with performance annotations, like @_noLocks, @_noAllocation. This is done recursively for all functions which are called from performance-annotated functions. rdar://83882635
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The purpose of performance annotations are to give the developer a tool to ensure that a certain piece of code meets certain performance characteristics.
If an annotated function contains some code which requires unwanted runtime operations, the compilation will fail with an error explaining the reason.
This PR contains a first prototype implementation of the feature:
@_noLocksand@_noAllocationFor now, the new feature is gated with an option
-experimental-performance-annotations.rdar://83882635