Merge pull request #38729 from varungandhi-apple/vg-tweak-docs

[docs] Make some corrections and additions to UnderscoredAttributes.md

Author: varungandhi-apple

docs/ReferenceGuides/UnderscoredAttributes.md

@@ -39,6 +39,14 @@ Most notably, default argument expressions are implicitly
 `@_alwaysEmitIntoClient`, which means that adding a default argument to a
 function which did not have one previously does not break ABI.
 
+## `@_assemblyVision`
+
+Forces emission of assembly vision remarks for a function or method, showing
+where various runtime calls and performance impacting hazards are in the code
+at source level after optimization.
+
+Adding this attribute to a type leads to remarks being emitted for all methods.
+
 ## `@_borrowed`
 
 Indicates that the [conservative access pattern](/docs/Lexicon.md#access-pattern)
@@ -95,15 +103,15 @@ extension Text {
 }
 ```
 
-## `@_dynamicReplacement(for:)`
+## `@_dynamicReplacement(for: targetFunc(label:))`
 
 Marks a function as the dynamic replacement for another `dynamic` function.
 This is similar to method swizzling in other languages such as Objective-C,
 except that the replacement happens at program start (or loading a shared
 library), instead of at an arbitrary point in time.
 
 For more details, see the forum post on
-[Dynamic method replacement](https://forums.swift.org/t/dynamic-method-replacement/16619).
+[dynamic method replacement](https://forums.swift.org/t/dynamic-method-replacement/16619).
 
 ## `@_distributedActorIndependent`
 
@@ -134,7 +142,7 @@ This attribute is most commonly used by overlays.
 
 ```swift
 // module M
-func f() {}
+public func f() {}
 
 // module N
 @_exported import M
@@ -270,11 +278,6 @@ of the closure. This is different from the typical behavior, where the closure
 may be runnable anywhere unless its type specifically declares that it will
 run on a specific actor.
 
-This new attribute can be used on parameters of `@Sendable async` type
-to indicate that the closures arguments passed to such parameters
-should inherit the actor context where they are formed, which is not
-the normal behavior for `@Sendable` closures.
-
 ## `@_inheritsConvenienceInitializers`
 
 An attribute that signals that a class declaration inherits its convenience
@@ -289,7 +292,6 @@ Indicates that a protocol is a marker protocol. Marker protocols represent some
 meaningful property at compile-time but have no runtime representation.
 
 For more details, see [SE-0302](https://github.com/apple/swift-evolution/blob/main/proposals/0302-concurrent-value-and-concurrent-closures.md#marker-protocols), which introduces marker protocols.
-
 At the moment, the language only has one marker protocol: `Sendable`.
 
 Fun fact: Rust has a very similar concept called

include/swift/AST/Attr.def

@@ -670,6 +670,9 @@ SIMPLE_DECL_ATTR(_assemblyVision, EmitAssemblyVisionRemarks,
   ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   120)
 
+// If you're adding a new underscored attribute here, please document it in
+// docs/ReferenceGuides/UnderscoredAttributes.md.
+
 #undef TYPE_ATTR
 #undef DECL_ATTR_ALIAS
 #undef CONTEXTUAL_DECL_ATTR_ALIAS