Merge pull request #37018 from mikeash/remove-dynamic-class-is-swift-mask

[Runtime] Remove the _swift_classIsSwiftMask variable.

Author: mikeash

include/swift/Runtime/BackDeployment.h

@@ -100,34 +100,21 @@
 /// from ObjC classes?
 #ifndef SWIFT_CLASS_IS_SWIFT_MASK
 
-// Non-Apple platforms always use 1.
-# if !defined(__APPLE__)
-#  define SWIFT_CLASS_IS_SWIFT_MASK 1ULL
-
-// Builds for Swift-in-the-OS always use 2.
-# elif SWIFT_BNI_OS_BUILD
-#  define SWIFT_CLASS_IS_SWIFT_MASK 2ULL
-
-// Builds for Xcode always use 1.
-# elif SWIFT_BNI_XCODE_BUILD
-#  define SWIFT_CLASS_IS_SWIFT_MASK 1ULL
-
 // Compatibility hook libraries cannot rely on the "is swift" bit being either
 // value, since they must work with both OS and Xcode versions of the libraries.
 // Generate a reference to a nonexistent symbol so that we get obvious linker
 // errors if we try.
-# elif SWIFT_COMPATIBILITY_LIBRARY
+# if SWIFT_COMPATIBILITY_LIBRARY
 extern uintptr_t __COMPATIBILITY_LIBRARIES_CANNOT_CHECK_THE_IS_SWIFT_BIT_DIRECTLY__;
 #  define SWIFT_CLASS_IS_SWIFT_MASK __COMPATIBILITY_LIBRARIES_CANNOT_CHECK_THE_IS_SWIFT_BIT_DIRECTLY__
 
-// Other builds (such as local builds on developers' computers)
-// dynamically choose the bit at runtime based on the current OS
-// version.
+// Apple platforms always use 2
+# elif defined(__APPLE__)
+#  define SWIFT_CLASS_IS_SWIFT_MASK 2ULL
+
+// Non-Apple platforms always use 1.
 # else
-#  define SWIFT_CLASS_IS_SWIFT_MASK _swift_classIsSwiftMask
-#  define SWIFT_CLASS_IS_SWIFT_MASK_GLOBAL_VARIABLE 1
-#  define SWIFT_BUILD_HAS_BACK_DEPLOYMENT 1
-#  include "BackDeployment.h"
+#  define SWIFT_CLASS_IS_SWIFT_MASK 1ULL
 
 # endif
 #endif

include/swift/Runtime/Config.h

@@ -30,7 +30,6 @@ set(swift_runtime_sources
     AnyHashableSupport.cpp
     Array.cpp
     AutoDiffSupport.cpp
-    BackDeployment.cpp
     Bincompat.cpp
     Casting.cpp
     CygwinPort.cpp