Add @effects(releasenone) documentation.

Author: aschwaighofer

docs/HighLevelSILOptimizations.rst

@@ -341,6 +341,50 @@ readonly
   eliminated, but cannot be reordered or folded in a way that would
   move calls to the readnone function across side effects.
 
+releasenone
+
+  function has side effects, it can read or write global state, or state
+  reachable from its arguments. It can however be assumed that no externally
+  visible release has happened (i.e it is allowed for a ``releasenone``
+  function to allocate and destruct an object in its implementation as long as
+  this is does not cause an release of an object visible outside of the
+  implementation).
+
+  Examples
+  ::
+  class SomeObject {
+    final var x: Int = 3
+  }
+  var global = SomeObject()
+
+  class SomeOtherObject {
+    var x: Int = 2
+    deinit {
+      global = SomeObject()
+    }
+  }
+
+  @effects(releasenone)
+  func validReleaseNoneFunction(x: Int) -> Int {
+    global.x = 5
+    return x + 2
+  }
+
+  @effects(releasenone)
+  func validReleaseNoneFunction(x: Int) -> Int {
+    var notExternallyVisibleObject = SomeObject()
+    return x +  notExternallyVisibleObject.x
+  }
+
+  func notAReleaseNoneFunction(x: Int, y: SomeObject) -> Int {
+    return x + y.x
+  }
+
+  func notAReleaseNoneFunction(x: Int) -> Int {
+    var releaseExternallyVisible = SomeOtherObject()
+    return x + releaseExternallyVisible.x
+  }
+
 readwrite
 
   function has side effects and the optimizer can't assume anything.