Resolve merge conflicts for github main -> next automerger.

Author: stephentyrone

Diff for: CMakeLists.txt

@@ -250,6 +250,10 @@ option(SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER
        "Use the host compiler and not the internal clang to build the swift runtime"
        FALSE)
 
+option(SWIFT_RUN_TESTS_WITH_HOST_COMPILER
+       "Run tests against the host compiler and not the just built swift"
+       FALSE)
+
 set(SWIFT_SDKS "" CACHE STRING
     "If non-empty, limits building target binaries only to specified SDKs (despite other SDKs being available)")
 

Diff for: README.md

@@ -10,6 +10,7 @@
 | **Ubuntu 18.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-18_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04)|
 | **Ubuntu 20.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04)|
 | **CentOS 8** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-centos-8/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-centos-8)|[![Build Status](https://ci.swift.org/job/oss-swift-package-centos-8/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-centos-8)|
+| **CentOS 7** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-centos-7/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-centos-7)|[![Build Status](https://ci.swift.org/job/oss-swift-package-centos-7/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-centos-7)|
 | **Amazon Linux 2** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-amazon-linux-2/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-amazon-linux-2)|[![Build Status](https://ci.swift.org/job/oss-swift-package-amazon-linux-2/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-amazon-linux-2)|
 
 **Swift Community-Hosted CI Platforms**
@@ -26,13 +27,6 @@
 |**[Windows 2019 (VS 2017)](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_windows_2019.json)** | x86_64 | [![Build Status](https://ci-external.swift.org/job/oss-swift-windows-x86_64/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-windows-x86_64)|
 |**[Windows 2019 (VS 2019)](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_windows_2019_VS2019.json)** | x86_64 | [![Build Status](https://ci-external.swift.org/job/oss-swift-windows-x86_64-vs2019/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-windows-x86_64-vs2019)|
 
-**Swift TensorFlow Community-Hosted CI Platforms**
-
-| **OS** | **Architecture** | **Build** |
-|---|:---:|:---:|
-|**[Ubuntu 18.04](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_ubuntu_18_04_tensorflow.json)** | x86_64 |[![Build Status](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-18.04-tensorflow/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-18.04-tensorflow)|
-|**[macOS 10.13](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_macos_high_sierra_tensorflow.json)** | x86_64 |[![Build Status](https://ci-external.swift.org/job/oss-swift-RA-macOS-tensorflow/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-macOS-tensorflow)|
-
 ## Welcome to Swift
 
 Swift is a high-performance system programming language.  It has a clean

Diff for: docs/Lexicon.md

@@ -67,6 +67,17 @@ and the combination of module path + access path is an "import path".)
 
 See `ImportPath` and the types nested inside it for more on this.
 
+## access pattern
+
+Defines how some particular storage (a property or a subscript) is accessed.
+For example, when accessing a property `let y = a.x`, the compiler could potentially
+use `get` accessor or the `_read` accessor. Similarly, for a modification like
+`a.x += 1`, the compiler could use `get` + `set` or it could use `_modify`.
+
+The access pattern can differ for call-sites which can/cannot see the underlying
+implementation. Clients which cannot see the underlying implementation are said
+to use the conservative access pattern.
+
 ## archetype
 
 A placeholder for a generic parameter or an associated type within a
@@ -476,6 +487,38 @@ See [mandatory passes](#mandatory-passes--mandatory-optimizations).
 An implicit representation change that occurs when a value is used with
 a different [abstraction pattern](#abstraction-pattern) from its current representation.
 
+## realization
+
+The process of initializing an ObjC class for use by the ObjC runtime.
+This consists of allocating runtime tracking data, fixing up method lists
+and attaching categories.
+
+This is distinct from the initialization performed by `+initialize`, which
+happens only when the first message (other than `+load`) is sent to the class.
+
+The order of operations is: realization, followed by `+load` (if present),
+followed by `+initialize`. There are few cases where these can happen
+at different times.
+
+- Common case (no `+load` or special attributes): Realization is lazy and
+  happens when the first message is sent to a class. After that, `+initialize`
+  is run.
+- If the class has a `+load` method: `+load`, as the name suggests, runs at
+  load time; it is the ObjC equivalent of a static initializer in C++. For
+  such a class, realization eagerly happens at load time before `+load` runs.
+  (Fun aside: C++ static initializers run after `+load`.) `+initialize` still
+  runs lazily on the first message.
+- If the class is marked [`@_objc_non_lazy_realization`](/docs/ReferenceGuides/UnderscoredAttributes.md#_objc_non_lazy_realization):
+  Realization happens at load time. `+initialize` still runs lazily on the first
+  message.
+
+It's possible to create a class that is realized but not initialized by
+using a runtime function like `objc_getClass` before the class has been used.
+
+See also: Mike Ash's blog post on
+[Objective-C Class Loading and Initialization](https://www.mikeash.com/pyblog/friday-qa-2009-05-22-objective-c-class-loading-and-initialization.html),
+which covers `+load` and `+initialize` in more detail.
+
 ## refutable pattern
 
 A pattern that may not always match. These include patterns such as:

Diff for: docs/README.md

@@ -177,6 +177,8 @@ documentation, please create a thread on the Swift forums under the
   <!-- NOTE: Outdated -->
 - [Lexicon.md](/docs/Lexicon.md):
   Canonical reference for terminology used throughout the project.
+- [UnderscoredAttributes.md](/docs/ReferenceGuides/UnderscoredAttributes.md):
+  Documents semantics for underscored (unstable) attributes.
 
 ### ABI