diff --git a/benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake b/benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake
index 7c5387bb5ccd6..2a542c9cd2291 100644
--- a/benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake
+++ b/benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake
@@ -716,9 +716,6 @@ function(swift_benchmark_compile)
 
   if(NOT SWIFT_BENCHMARK_BUILT_STANDALONE)
     set(stdlib_dependencies "swift-frontend" "swiftCore-${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}")
-    if((SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS) AND SWIFT_BUILD_SDK_OVERLAY)
-      list(APPEND stdlib_dependencies "swiftDarwin-${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}")
-    endif()
     foreach(stdlib_dependency ${UNIVERSAL_LIBRARY_NAMES_${SWIFT_BENCHMARK_COMPILE_PLATFORM}})
       string(FIND "${stdlib_dependency}" "Unittest" find_output)
       if("${find_output}" STREQUAL "-1")
diff --git a/cmake/modules/DarwinSDKs.cmake b/cmake/modules/DarwinSDKs.cmake
index 20d555b74751c..1605687f6d9c2 100644
--- a/cmake/modules/DarwinSDKs.cmake
+++ b/cmake/modules/DarwinSDKs.cmake
@@ -38,11 +38,7 @@ if(swift_build_freestanding AND (SWIFT_FREESTANDING_FLAVOR STREQUAL "apple"))
   configure_target_variant(FREESTANDING-R  "FREESTANDING Release"         FREESTANDING R  "Release")
   configure_target_variant(FREESTANDING-S  "FREESTANDING MinSizeRelease"  FREESTANDING S  "MinSizeRelease")
 
-  if(SWIFT_BUILD_SDK_OVERLAY)
-    set(SWIFT_FREESTANDING_TEST_DEPENDENCIES "Darwin")
-  else()
-    set(SWIFT_FREESTANDING_TEST_DEPENDENCIES "")
-  endif()
+  set(SWIFT_FREESTANDING_TEST_DEPENDENCIES "")
 endif()
 
 # Compatible cross-compile SDKS for Darwin OSes: IOS, IOS_SIMULATOR, TVOS,
diff --git a/stdlib/private/OSLog/CMakeLists.txt b/stdlib/private/OSLog/CMakeLists.txt
index 21cab695c781d..4941b39c89598 100644
--- a/stdlib/private/OSLog/CMakeLists.txt
+++ b/stdlib/private/OSLog/CMakeLists.txt
@@ -1,7 +1,4 @@
 set(swift_oslog_darwin_dependencies "")
-if(SWIFT_BUILD_SDK_OVERLAY)
-    list(APPEND swift_oslog_darwin_dependencies "Darwin")
-endif()
 if (SWIFT_ENABLE_EXPERIMENTAL_CONCURRENCY)
     list(APPEND swift_oslog_darwin_dependencies "_Concurrency")
 endif()
@@ -12,10 +9,8 @@ if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_oslog_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/private/StdlibUnittest/CMakeLists.txt b/stdlib/private/StdlibUnittest/CMakeLists.txt
index a54fc7b006777..a8dc3ad1820e8 100644
--- a/stdlib/private/StdlibUnittest/CMakeLists.txt
+++ b/stdlib/private/StdlibUnittest/CMakeLists.txt
@@ -1,17 +1,11 @@
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swift_stdlib_unittest_darwin_dependencies Darwin)
-else()
 set(swift_stdlib_unittest_darwin_dependencies)
-endif()
 
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_stdlib_unittest_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/private/SwiftPrivate/CMakeLists.txt b/stdlib/private/SwiftPrivate/CMakeLists.txt
index 585a0b36c86de..3d6b75d2cbd6f 100644
--- a/stdlib/private/SwiftPrivate/CMakeLists.txt
+++ b/stdlib/private/SwiftPrivate/CMakeLists.txt
@@ -2,20 +2,14 @@ set(swift_swiftprivate_compile_flags
     "-parse-stdlib"
     "-Xfrontend" "-disable-access-control")
 
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swift_swiftprivate_darwin_dependencies Darwin)
-else()
 set(swift_swiftprivate_darwin_dependencies)
-endif()
 
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_swiftprivate_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt b/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt
index 22adfe2cb6af2..dd7f9c148453a 100644
--- a/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt
+++ b/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt
@@ -14,20 +14,14 @@ else()
   set(swift_private_libc_extras_incorporate_object_libraries "swiftCommandLineSupport")
 endif()
 
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swift_private_libc_extras_darwin_dependencies Darwin)
-else()
 set(swift_private_libc_extras_darwin_dependencies)
-endif()
 
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_private_libc_extras_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt b/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt
index 5d005a783d595..d74a3fb627f71 100644
--- a/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt
+++ b/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt
@@ -1,17 +1,11 @@
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swift_private_thread_extras_darwin_dependencies Darwin)
-else()
 set(swift_private_thread_extras_darwin_dependencies)
-endif()
 
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_private_thread_extras_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/private/SwiftReflectionTest/CMakeLists.txt b/stdlib/private/SwiftReflectionTest/CMakeLists.txt
index d9474ac61bd44..8cbe7c8a6ee6d 100644
--- a/stdlib/private/SwiftReflectionTest/CMakeLists.txt
+++ b/stdlib/private/SwiftReflectionTest/CMakeLists.txt
@@ -1,17 +1,11 @@
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swift_reflection_test_darwin_dependencies Darwin)
-else()
 set(swift_reflection_test_darwin_dependencies)
-endif()
 
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_reflection_test_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/public/Cxx/std/CMakeLists.txt b/stdlib/public/Cxx/std/CMakeLists.txt
index c8a4b2e1def2b..010dad07b3ba9 100644
--- a/stdlib/public/Cxx/std/CMakeLists.txt
+++ b/stdlib/public/Cxx/std/CMakeLists.txt
@@ -19,15 +19,6 @@ add_dependencies(sdk-overlay CxxStdlib-apinotes)
 add_dependencies(compiler CxxStdlib-apinotes)
 
 
-# Swift compiler currently assumes that the Darwin overlay is a dependency of
-# CxxStdlib, and fails to build CxxStdlib if Darwin.swiftmodule in build dir
-# is built with a different (older) version of the compiler. To workaround this,
-# declare the Darwin overlay as a dependency of CxxStdlib.
-set(swift_cxxstdlib_darwin_dependencies)
-if(SWIFT_BUILD_STDLIB AND SWIFT_BUILD_SDK_OVERLAY)
-  set(swift_cxxstdlib_darwin_dependencies Darwin)
-endif()
-
 set(swift_cxxstdlib_dependencies)
 if(NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT)
   set(swift_cxxstdlib_dependencies _Builtin_float)
@@ -44,12 +35,6 @@ add_swift_target_library(swiftCxxStdlib STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_O
     String.swift
 
     SWIFT_MODULE_DEPENDS Cxx ${swift_cxxstdlib_dependencies}
-    SWIFT_MODULE_DEPENDS_IOS ${swift_cxxstdlib_darwin_dependencies}
-    SWIFT_MODULE_DEPENDS_OSX ${swift_cxxstdlib_darwin_dependencies}
-    SWIFT_MODULE_DEPENDS_TVOS ${swift_cxxstdlib_darwin_dependencies}
-    SWIFT_MODULE_DEPENDS_WATCHOS ${swift_cxxstdlib_darwin_dependencies}
-    SWIFT_MODULE_DEPENDS_XROS ${swift_cxxstdlib_darwin_dependencies}
-    SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_cxxstdlib_darwin_dependencies}
     SWIFT_MODULE_DEPENDS_ANDROID Android
 
     SWIFT_COMPILE_FLAGS ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS} ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
diff --git a/stdlib/public/Differentiation/CMakeLists.txt b/stdlib/public/Differentiation/CMakeLists.txt
index 16a296bbbe772..f7149eacb0a8e 100644
--- a/stdlib/public/Differentiation/CMakeLists.txt
+++ b/stdlib/public/Differentiation/CMakeLists.txt
@@ -16,12 +16,6 @@ else()
 set(swiftDifferentiationSIMDFiles)
 endif()
 
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swiftDifferentiationDarwinDependencies Darwin)
-else()
-set(swiftDifferentiationDarwinDependencies)
-endif()
-
 add_swift_target_library(swift_Differentiation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_STDLIB
   Differentiable.swift
   DifferentialOperators.swift
@@ -37,11 +31,6 @@ add_swift_target_library(swift_Differentiation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPE
     TgmathDerivatives.swift.gyb
     ${swiftDifferentiationSIMDFiles}
 
-  SWIFT_MODULE_DEPENDS_OSX ${swiftDifferentiationDarwinDependencies}
-  SWIFT_MODULE_DEPENDS_IOS ${swiftDifferentiationDarwinDependencies}
-  SWIFT_MODULE_DEPENDS_TVOS ${swiftDifferentiationDarwinDependencies}
-  SWIFT_MODULE_DEPENDS_WATCHOS ${swiftDifferentiationDarwinDependencies}
-  SWIFT_MODULE_DEPENDS_XROS ${swiftDifferentiationDarwinDependencies}
   SWIFT_MODULE_DEPENDS_ANDROID Android
   SWIFT_MODULE_DEPENDS_LINUX Glibc
   SWIFT_MODULE_DEPENDS_LINUX_STATIC Musl
diff --git a/stdlib/public/Distributed/CMakeLists.txt b/stdlib/public/Distributed/CMakeLists.txt
index aec0c14f7c2b3..2e4970c3e4e7a 100644
--- a/stdlib/public/Distributed/CMakeLists.txt
+++ b/stdlib/public/Distributed/CMakeLists.txt
@@ -10,20 +10,14 @@
 #
 #===----------------------------------------------------------------------===#
 
-if(SWIFT_BUILD_SDK_OVERLAY)
-set(swift_distributed_darwin_dependencies Darwin)
-else()
 set(swift_distributed_darwin_dependencies)
-endif()
 
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND swift_distributed_darwin_dependencies _Builtin_float)
 endif()
 
diff --git a/stdlib/public/Platform/CMakeLists.txt b/stdlib/public/Platform/CMakeLists.txt
index 9ae7a977ac400..0faab2f191a53 100644
--- a/stdlib/public/Platform/CMakeLists.txt
+++ b/stdlib/public/Platform/CMakeLists.txt
@@ -4,130 +4,11 @@ set(swift_platform_sources
 set(swift_platform_gyb_sources
     tgmath.swift.gyb)
 
-set(darwin_depends)
-if(NOT BUILD_STANDALONE)
-  # This is overly conservative, but we have so few API notes files that
-  # haven't migrated to the Swift repo that it's probably fine in practice.
-  list(APPEND darwin_depends copy_apinotes)
-endif()
-
 set(swift_platform_compile_flags)
 if(SWIFT_ENABLE_REFLECTION)
   list(APPEND swift_platform_compile_flags "-DSWIFT_ENABLE_REFLECTION")
 endif()
 
-set(swiftDarwin_target_sdks ALL_APPLE_PLATFORMS)
-if(SWIFT_FREESTANDING_FLAVOR STREQUAL "apple" AND NOT SWIFT_FREESTANDING_IS_DARWIN)
-  set(swiftDarwin_target_sdks ALL_APPLE_PLATFORMS FREESTANDING)
-endif()
-
-set(swiftDarwin_common_options
-      IS_SDK_OVERLAY
-      ${swift_platform_sources}
-      POSIXError.swift
-      MachError.swift
-
-      "${SWIFT_SOURCE_DIR}/stdlib/linker-support/magic-symbols-for-install-name.c"
-
-      GYB_SOURCES
-        ${swift_platform_gyb_sources}
-        Darwin.swift.gyb
-
-      SWIFT_COMPILE_FLAGS
-        ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}
-        ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
-        -Xfrontend -disable-objc-attr-requires-foundation-module
-        ${swift_platform_compile_flags}
-      LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}"
-      DEPENDS ${darwin_depends})
-
-
-if(BOOTSTRAPPING_MODE STREQUAL "BOOTSTRAPPING" AND
-   SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS)
-
-  set(swiftDarwin_common_bootstrapping_options
-      ${swiftDarwin_common_options}
-      SHARED
-      IS_STDLIB
-      SDK ${SWIFT_HOST_VARIANT_SDK}
-      ARCHITECTURE ${SWIFT_HOST_VARIANT_ARCH}
-      INSTALL_IN_COMPONENT "never_install")
-
-  set(b0_deps swiftCore-bootstrapping0)
-  set(b1_deps swiftCore-bootstrapping1)
-  if(CMAKE_BUILD_TYPE STREQUAL "Debug")
-    set(b0_deps ${b0_deps} swiftSwiftOnoneSupport-bootstrapping0)
-    set(b1_deps ${b1_deps} swiftSwiftOnoneSupport-bootstrapping1)
-  endif()
-
-  add_swift_target_library_single(swiftDarwin-bootstrapping0 swiftDarwin
-      ${swiftDarwin_common_bootstrapping_options}
-      FILE_DEPENDS ${b0_deps}
-      BOOTSTRAPPING 0)
-
-  add_swift_target_library_single(swiftDarwin-bootstrapping1 swiftDarwin
-      ${swiftDarwin_common_bootstrapping_options}
-      FILE_DEPENDS ${b1_deps}
-      BOOTSTRAPPING 1)
-endif()
-
-add_swift_target_library(swiftDarwin ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES}
-    ${swiftDarwin_common_options}
-    TARGET_SDKS "${swiftDarwin_target_sdks}"
-    INSTALL_IN_COMPONENT sdk-overlay
-    MACCATALYST_BUILD_FLAVOR "zippered"
-    INSTALL_BINARY_SWIFTMODULE FALSE)
-
-if(SWIFT_SHOULD_BUILD_EMBEDDED_STDLIB)
-  set(SWIFT_ENABLE_REFLECTION OFF)
-
-  add_custom_target(embedded-darwin)
-  add_dependencies(embedded-libraries embedded-darwin)
-  foreach(entry ${EMBEDDED_STDLIB_TARGET_TRIPLES})
-    string(REGEX REPLACE "[ \t]+" ";" list "${entry}")
-    list(GET list 0 arch)
-    list(GET list 1 mod)
-    list(GET list 2 triple)
-
-    if(NOT "${mod}" MATCHES "-macos$")
-      continue()
-    endif()
-
-    set(SWIFT_SDK_embedded_ARCH_${arch}_MODULE "${mod}")
-    set(SWIFT_SDK_embedded_LIB_SUBDIR "embedded")
-    set(SWIFT_SDK_embedded_ARCH_${arch}_TRIPLE "${triple}")
-    set(SWIFT_SDK_embedded_PATH ${SWIFT_SDK_OSX_PATH})
-    set(SWIFT_SDK_embedded_ARCH_${arch}_PATH ${SWIFT_SDK_OSX_PATH})
-    set(SWIFT_SDK_embedded_USE_ISYSROOT TRUE)
-    add_swift_target_library_single(
-      embedded-darwin-${mod}
-      swiftDarwin
-      ONLY_SWIFTMODULE
-      IS_SDK_OVERLAY IS_FRAGILE
-
-      Platform.swift
-      TiocConstants.swift
-      POSIXError.swift
-      MachError.swift
-
-      GYB_SOURCES
-        tgmath.swift.gyb
-        Darwin.swift.gyb
-      
-      SWIFT_COMPILE_FLAGS
-        -Xcc -ffreestanding -enable-experimental-feature Embedded
-      C_COMPILE_FLAGS
-        -ffreestanding
-      MODULE_DIR "${CMAKE_BINARY_DIR}/lib/swift/embedded"
-      SDK "embedded"
-      ARCHITECTURE "${arch}"
-      DEPENDS embedded-stdlib-${mod}
-      INSTALL_IN_COMPONENT stdlib
-      )
-    add_dependencies(embedded-darwin embedded-darwin-${mod})
-  endforeach()
-endif()
-
 set(swiftGlibc_target_sdks CYGWIN FREEBSD OPENBSD LINUX HAIKU)
 if(SWIFT_FREESTANDING_FLAVOR STREQUAL "linux")
   set(swiftGlibc_target_sdks CYGWIN FREEBSD OPENBSD LINUX HAIKU FREESTANDING)
diff --git a/stdlib/public/Platform/Darwin.swift.gyb b/stdlib/public/Platform/Darwin.swift.gyb
deleted file mode 100644
index f0153220ff968..0000000000000
--- a/stdlib/public/Platform/Darwin.swift.gyb
+++ /dev/null
@@ -1,81 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
-//
-//===----------------------------------------------------------------------===//
-
-@_exported import Darwin // Clang module
-
-public let MAP_FAILED: UnsafeMutableRawPointer! = UnsafeMutableRawPointer(bitPattern: -1)
-
-//  Constants defined by <math.h>
-@available(swift, deprecated: 3.0, message: "Please use 'Double.pi' or '.pi' to get the value of correct type and avoid casting.")
-public let M_PI = Double.pi
-
-@available(swift, deprecated: 3.0, message: "Please use 'Double.pi / 2' or '.pi / 2' to get the value of correct type and avoid casting.")
-public let M_PI_2 = Double.pi / 2
-
-@available(swift, deprecated: 3.0, message: "Please use 'Double.pi / 4' or '.pi / 4' to get the value of correct type and avoid casting.")
-public let M_PI_4 = Double.pi / 4
-
-@available(swift, deprecated: 3.0, message: "Please use '2.squareRoot()'.")
-public let M_SQRT2 = 2.squareRoot()
-
-@available(swift, deprecated: 3.0, message: "Please use '0.5.squareRoot()'.")
-public let M_SQRT1_2 = 0.5.squareRoot()
-
-//  Constants defined by <float.h>
-@available(swift, deprecated: 3.0, message: "Please use 'T.radix' to get the radix of a FloatingPoint type 'T'.")
-public let FLT_RADIX = Double.radix
-
-%for type, prefix in [('Float', 'FLT'), ('Double', 'DBL'), ('Float80', 'LDBL')]:
-% if type == "Float80":
-#if arch(i386) || arch(x86_64)
-% end
-//  Where does the 1 come from? C counts the usually-implicit leading
-//  significand bit, but Swift does not. Neither is really right or wrong.
-@available(swift, deprecated: 3.0, message: "Please use '${type}.significandBitCount + 1'.")
-public let ${prefix}_MANT_DIG = ${type}.significandBitCount + 1
-
-//  Where does the 1 come from? C models floating-point numbers as having a
-//  significand in [0.5, 1), but Swift (following IEEE 754) considers the
-//  significand to be in [1, 2). This rationale applies to ${prefix}_MIN_EXP
-//  as well.
-@available(swift, deprecated: 3.0, message: "Please use '${type}.greatestFiniteMagnitude.exponent + 1'.")
-public let ${prefix}_MAX_EXP = ${type}.greatestFiniteMagnitude.exponent + 1
-
-@available(swift, deprecated: 3.0, message: "Please use '${type}.leastNormalMagnitude.exponent + 1'.")
-public let ${prefix}_MIN_EXP = ${type}.leastNormalMagnitude.exponent + 1
-
-@available(swift, deprecated: 3.0, message: "Please use '${type}.greatestFiniteMagnitude' or '.greatestFiniteMagnitude'.")
-public let ${prefix}_MAX = ${type}.greatestFiniteMagnitude
-
-@available(swift, deprecated: 3.0, message: "Please use '${type}.ulpOfOne' or '.ulpOfOne'.")
-public let ${prefix}_EPSILON = ${type}.ulpOfOne
-
-@available(swift, deprecated: 3.0, message: "Please use '${type}.leastNormalMagnitude' or '.leastNormalMagnitude'.")
-public let ${prefix}_MIN = ${type}.leastNormalMagnitude
-
-@available(swift, deprecated: 3.0, message: "Please use '${type}.leastNonzeroMagnitude' or '.leastNonzeroMagnitude'.")
-public let ${prefix}_TRUE_MIN = ${type}.leastNonzeroMagnitude
-
-% if type == "Float80":
-#endif
-% end
-%end
-
-// Macros defined in bsd/sys/proc.h that do not import into Swift.
-extension extern_proc {
-    // #define p_starttime p_un.__p_starttime
-    @_transparent
-    public var p_starttime: timeval {
-        get { return self.p_un.__p_starttime }
-        set { self.p_un.__p_starttime = newValue }
-    }
-}
diff --git a/stdlib/public/Platform/MachError.swift b/stdlib/public/Platform/MachError.swift
deleted file mode 100644
index 1dfecd66a5f1c..0000000000000
--- a/stdlib/public/Platform/MachError.swift
+++ /dev/null
@@ -1,205 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
-//
-//===----------------------------------------------------------------------===//
-
-#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && _runtime(_ObjC)
-/// Enumeration describing Mach error codes.
-@objc
-public enum MachErrorCode : Int32 {
-  case success                  = 0
-
-  /// Specified address is not currently valid.
-  case invalidAddress           = 1
-
-  /// Specified memory is valid, but does not permit the required
-  /// forms of access.
-  case protectionFailure        = 2
-
-  /// The address range specified is already in use, or no address
-  /// range of the size specified could be found.  
-  case noSpace                  = 3
-
-  /// The function requested was not applicable to this type of
-  /// argument, or an argument is invalid.
-  case invalidArgument          = 4
-
-  /// The function could not be performed.  A catch-all.
-  case failure                  = 5
-
-  /// A system resource could not be allocated to fulfill this
-  /// request.  This failure may not be permanent.
-  case resourceShortage         = 6
-
-  /// The task in question does not hold receive rights for the port
-  /// argument.
-  case notReceiver              = 7
-
-  /// Bogus access restriction.
-  case noAccess                 = 8
-
-  /// During a page fault, the target address refers to a memory
-  /// object that has been destroyed.  This failure is permanent.
-  case memoryFailure            = 9
-
-  /// During a page fault, the memory object indicated that the data
-  /// could not be returned.  This failure may be temporary; future
-  /// attempts to access this same data may succeed, as defined by the
-  /// memory object.
-  case memoryError              = 10
-
-  /// The receive right is already a member of the portset.
-  case alreadyInSet             = 11
-
-  /// The receive right is not a member of a port set.
-  case notInSet                 = 12
-
-  /// The name already denotes a right in the task.
-  case nameExists               = 13
-
-  /// The operation was aborted.  Ipc code will catch this and reflect
-  /// it as a message error.
-  case aborted                  = 14
-
-  /// The name doesn't denote a right in the task.
-  case invalidName              = 15
-
-  /// Target task isn't an active task.
-  case invalidTask              = 16
-
-  /// The name denotes a right, but not an appropriate right.
-  case invalidRight             = 17
-
-  /// A blatant range error.
-  case invalidValue             = 18
-
-  /// Operation would overflow limit on user-references.
-  case userReferencesOverflow   = 19
-
-  /// The supplied (port) capability is improper.
-  case invalidCapability        = 20
-
-  /// The task already has send or receive rights for the port under
-  /// another name.
-  case rightExists              = 21
-
-  /// Target host isn't actually a host.
-  case invalidHost              = 22
-
-  /// An attempt was made to supply "precious" data for memory that is
-  /// already present in a memory object.
-  case memoryPresent            = 23
-
-  /// A page was requested of a memory manager via
-  /// memory_object_data_request for an object using a
-  /// MEMORY_OBJECT_COPY_CALL strategy, with the VM_PROT_WANTS_COPY
-  /// flag being used to specify that the page desired is for a copy
-  /// of the object, and the memory manager has detected the page was
-  /// pushed into a copy of the object while the kernel was walking
-  /// the shadow chain from the copy to the object. This error code is
-  /// delivered via memory_object_data_error and is handled by the
-  /// kernel (it forces the kernel to restart the fault). It will not
-  /// be seen by users.
-  case memoryDataMoved          = 24
-
-  /// A strategic copy was attempted of an object upon which a quicker
-  /// copy is now possible.  The caller should retry the copy using
-  /// vm_object_copy_quickly. This error code is seen only by the
-  /// kernel.
-  case memoryRestartCopy        = 25
-
-  /// An argument applied to assert processor set privilege was not a
-  /// processor set control port.
-  case invalidProcessorSet      = 26
-
-  /// The specified scheduling attributes exceed the thread's limits.
-  case policyLimit              = 27
-
-  /// The specified scheduling policy is not currently enabled for the
-  /// processor set.
-  case invalidPolicy            = 28
-
-  /// The external memory manager failed to initialize the memory object.
-  case invalidObject            = 29
-
-  /// A thread is attempting to wait for an event for which there is
-  /// already a waiting thread.
-  case alreadyWaiting           = 30
-
-  /// An attempt was made to destroy the default processor set.
-  case defaultSet               = 31
-
-  /// An attempt was made to fetch an exception port that is
-  /// protected, or to abort a thread while processing a protected
-  /// exception.
-  case exceptionProtected       = 32
-
-  /// A ledger was required but not supplied.
-  case invalidLedger            = 33
-
-  /// The port was not a memory cache control port.
-  case invalidMemoryControl     = 34
-
-  /// An argument supplied to assert security privilege was not a host
-  /// security port.
-  case invalidSecurity          = 35
-
-  /// thread_depress_abort was called on a thread which was not
-  /// currently depressed.
-  case notDepressed             = 36
-
-  /// Object has been terminated and is no longer available.
-  case terminated               = 37
-
-  /// Lock set has been destroyed and is no longer available.
-  case lockSetDestroyed         = 38
-
-  /// The thread holding the lock terminated before releasing the lock.
-  case lockUnstable             = 39
-
-  /// The lock is already owned by another thread.
-  case lockOwned                = 40
-
-  /// The lock is already owned by the calling thread.
-  case lockOwnedSelf            = 41
-
-  /// Semaphore has been destroyed and is no longer available.
-  case semaphoreDestroyed       = 42
-
-  /// Return from RPC indicating the target server was terminated
-  /// before it successfully replied.
-  case rpcServerTerminated      = 43
-
-  /// Terminate an orphaned activation.
-  case rpcTerminateOrphan       = 44
-
-  /// Allow an orphaned activation to continue executing.
-  case rpcContinueOrphan        = 45
-
-  /// Empty thread activation (No thread linked to it).
-  case notSupported             = 46
-
-  /// Remote node down or inaccessible.
-  case nodeDown                 = 47
-
-  /// A signalled thread was not actually waiting.
-  case notWaiting               = 48
-
-  /// Some thread-oriented operation (semaphore_wait) timed out.
-  case operationTimedOut        = 49
-
-  /// During a page fault, indicates that the page was rejected as a
-  /// result of a signature check.
-  case codesignError            = 50
-
-  /// The requested property cannot be changed at this time.
-  case policyStatic             = 51
-}
-#endif // (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && _runtime(_ObjC)
diff --git a/stdlib/public/Platform/POSIXError.swift b/stdlib/public/Platform/POSIXError.swift
index a655bd655e4a5..b379fac5a20cc 100644
--- a/stdlib/public/Platform/POSIXError.swift
+++ b/stdlib/public/Platform/POSIXError.swift
@@ -10,260 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && _runtime(_ObjC)
-
-/// Enumeration describing POSIX error codes.
-@objc
-public enum POSIXErrorCode: Int32, Sendable {
-  /// Operation not permitted.
-  case EPERM           = 1
-  /// No such file or directory.
-  case ENOENT          = 2
-  /// No such process.
-  case ESRCH           = 3
-  /// Interrupted system call.
-  case EINTR           = 4
-  /// Input/output error.
-  case EIO             = 5
-  /// Device not configured.
-  case ENXIO           = 6
-  /// Argument list too long.
-  case E2BIG           = 7
-  /// Exec format error.
-  case ENOEXEC         = 8
-  /// Bad file descriptor.
-  case EBADF           = 9
-  /// No child processes.
-  case ECHILD          = 10
-  /// Resource deadlock avoided.
-  case EDEADLK         = 11
-  /// 11 was EAGAIN.
-  /// Cannot allocate memory.
-  case ENOMEM          = 12
-  /// Permission denied.
-  case EACCES          = 13
-  /// Bad address.
-  case EFAULT          = 14
-  /// Block device required.
-  case ENOTBLK         = 15
-  /// Device / Resource busy.
-  case EBUSY           = 16
-  /// File exists.
-  case EEXIST          = 17
-  /// Cross-device link.
-  case EXDEV           = 18
-  /// Operation not supported by device.
-  case ENODEV          = 19
-  /// Not a directory.
-  case ENOTDIR         = 20
-  /// Is a directory.
-  case EISDIR          = 21
-  /// Invalid argument.
-  case EINVAL          = 22
-  /// Too many open files in system.
-  case ENFILE          = 23
-  /// Too many open files.
-  case EMFILE          = 24
-  /// Inappropriate ioctl for device.
-  case ENOTTY          = 25
-  /// Text file busy.
-  case ETXTBSY         = 26
-  /// File too large.
-  case EFBIG           = 27
-  /// No space left on device.
-  case ENOSPC          = 28
-  /// Illegal seek.
-  case ESPIPE          = 29
-  /// Read-only file system.
-  case EROFS           = 30
-  /// Too many links.
-  case EMLINK          = 31
-  /// Broken pipe.
-  case EPIPE           = 32
-    
-  /// math software.
-  /// Numerical argument out of domain.
-  case EDOM            = 33
-  /// Result too large.
-  case ERANGE          = 34
-    
-  /// non-blocking and interrupt i/o.
-  /// Resource temporarily unavailable.
-  case EAGAIN          = 35
-  /// Operation would block.
-  public static var EWOULDBLOCK: POSIXErrorCode { return EAGAIN }
-  /// Operation now in progress.
-  case EINPROGRESS     = 36
-  /// Operation already in progress.
-  case EALREADY        = 37
-    
-  /// ipc/network software -- argument errors.
-  /// Socket operation on non-socket.
-  case ENOTSOCK        = 38
-  /// Destination address required.
-  case EDESTADDRREQ    = 39
-  /// Message too long.
-  case EMSGSIZE        = 40
-  /// Protocol wrong type for socket.
-  case EPROTOTYPE      = 41
-  /// Protocol not available.
-  case ENOPROTOOPT     = 42
-  /// Protocol not supported.
-  case EPROTONOSUPPORT = 43
-  /// Socket type not supported.
-  case ESOCKTNOSUPPORT = 44
-  /// Operation not supported.
-  case ENOTSUP         = 45
-  /// Protocol family not supported.
-  case EPFNOSUPPORT    = 46
-  /// Address family not supported by protocol family.
-  case EAFNOSUPPORT    = 47
-  /// Address already in use.
-  case EADDRINUSE      = 48
-  /// Can't assign requested address.
-  case EADDRNOTAVAIL   = 49
-    
-  /// ipc/network software -- operational errors
-  /// Network is down.
-  case ENETDOWN        = 50
-  /// Network is unreachable.
-  case ENETUNREACH     = 51
-  /// Network dropped connection on reset.
-  case ENETRESET       = 52
-  /// Software caused connection abort.
-  case ECONNABORTED    = 53
-  /// Connection reset by peer.
-  case ECONNRESET      = 54
-  /// No buffer space available.
-  case ENOBUFS         = 55
-  /// Socket is already connected.
-  case EISCONN         = 56
-  /// Socket is not connected.
-  case ENOTCONN        = 57
-  /// Can't send after socket shutdown.
-  case ESHUTDOWN       = 58
-  /// Too many references: can't splice.
-  case ETOOMANYREFS    = 59
-  /// Operation timed out.
-  case ETIMEDOUT       = 60
-  /// Connection refused.
-  case ECONNREFUSED    = 61
-    
-  /// Too many levels of symbolic links.
-  case ELOOP           = 62
-  /// File name too long.
-  case ENAMETOOLONG    = 63
-    
-  /// Host is down.
-  case EHOSTDOWN       = 64
-  /// No route to host.
-  case EHOSTUNREACH    = 65
-  /// Directory not empty.
-  case ENOTEMPTY       = 66
-    
-  /// quotas & mush.
-  /// Too many processes.
-  case EPROCLIM        = 67
-  /// Too many users.
-  case EUSERS          = 68
-  /// Disc quota exceeded.
-  case EDQUOT          = 69
-    
-  /// Network File System.
-  /// Stale NFS file handle.
-  case ESTALE          = 70
-  /// Too many levels of remote in path.
-  case EREMOTE         = 71
-  /// RPC struct is bad.
-  case EBADRPC         = 72
-  /// RPC version wrong.
-  case ERPCMISMATCH    = 73
-  /// RPC prog. not avail.
-  case EPROGUNAVAIL    = 74
-  /// Program version wrong.
-  case EPROGMISMATCH   = 75
-  /// Bad procedure for program.
-  case EPROCUNAVAIL    = 76
-    
-  /// No locks available.
-  case ENOLCK          = 77
-  /// Function not implemented.
-  case ENOSYS          = 78
-    
-  /// Inappropriate file type or format.
-  case EFTYPE          = 79
-  /// Authentication error.
-  case EAUTH           = 80
-  /// Need authenticator.
-  case ENEEDAUTH       = 81
-    
-  /// Intelligent device errors.
-  /// Device power is off.
-  case EPWROFF         = 82
-  /// Device error, e.g. paper out.
-  case EDEVERR         = 83
-    
-  /// Value too large to be stored in data type.
-  case EOVERFLOW       = 84
-
-  // MARK: Program loading errors.
-
-  /// Bad executable.
-  case EBADEXEC        = 85
-  /// Bad CPU type in executable.
-  case EBADARCH        = 86
-  /// Shared library version mismatch.
-  case ESHLIBVERS      = 87
-  /// Malformed Macho file.
-  case EBADMACHO       = 88
-    
-  /// Operation canceled.
-  case ECANCELED       = 89
-    
-  /// Identifier removed.
-  case EIDRM           = 90
-  /// No message of desired type.
-  case ENOMSG          = 91
-  /// Illegal byte sequence.
-  case EILSEQ          = 92
-  /// Attribute not found.
-  case ENOATTR         = 93
-    
-  /// Bad message.
-  case EBADMSG         = 94
-  /// Reserved.
-  case EMULTIHOP       = 95
-  /// No message available on STREAM.
-  case ENODATA         = 96
-  /// Reserved.
-  case ENOLINK         = 97
-  /// No STREAM resources.
-  case ENOSR           = 98
-  /// Not a STREAM.
-  case ENOSTR          = 99
-  /// Protocol error.
-  case EPROTO          = 100
-  /// STREAM ioctl timeout.
-  case ETIME           = 101
-    
-  /// No such policy registered.
-  case ENOPOLICY       = 103
-    
-  /// State not recoverable.
-  case ENOTRECOVERABLE = 104
-  /// Previous owner died.
-  case EOWNERDEAD      = 105
-  
-  /// Interface output queue is full.
-  case EQFULL          = 106
-  /// Must be equal largest errno.
-  public static var ELAST: POSIXErrorCode { return EQFULL }
-    
-  // FIXME: EOPNOTSUPP has different values depending on __DARWIN_UNIX03 and
-  // KERNEL.
-}
-
-#elseif os(Linux) || os(Android)
+#if os(Linux) || os(Android)
 
 /// Enumeration describing POSIX error codes.
 public enum POSIXErrorCode: Int32, Sendable {
diff --git a/stdlib/public/Platform/Platform.swift b/stdlib/public/Platform/Platform.swift
index 0c2d63a0cffdb..016461e90a997 100644
--- a/stdlib/public/Platform/Platform.swift
+++ b/stdlib/public/Platform/Platform.swift
@@ -13,77 +13,6 @@
 import SwiftShims
 import SwiftOverlayShims
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-//===----------------------------------------------------------------------===//
-// MacTypes.h
-//===----------------------------------------------------------------------===//
-
-public var noErr: OSStatus { return 0 }
-
-/// The `Boolean` type declared in MacTypes.h and used throughout Core
-/// Foundation.
-///
-/// The C type is a typedef for `unsigned char`.
-@frozen
-public struct DarwinBoolean : ExpressibleByBooleanLiteral {
-  @usableFromInline var _value: UInt8
-
-  @_transparent
-  public init(_ value: Bool) {
-    self._value = value ? 1 : 0
-  }
-
-  /// The value of `self`, expressed as a `Bool`.
-  @_transparent
-  public var boolValue: Bool {
-    return _value != 0
-  }
-
-  /// Create an instance initialized to `value`.
-  @_transparent
-  public init(booleanLiteral value: Bool) {
-    self.init(value)
-  }
-}
-
-#if SWIFT_ENABLE_REFLECTION
-extension DarwinBoolean : CustomReflectable {
-  /// Returns a mirror that reflects `self`.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: boolValue)
-  }
-}
-#endif
-
-@_unavailableInEmbedded
-extension DarwinBoolean : CustomStringConvertible {
-  /// A textual representation of `self`.
-  public var description: String {
-    return self.boolValue.description
-  }
-}
-
-extension DarwinBoolean : Equatable {
-  @_transparent
-  public static func ==(lhs: DarwinBoolean, rhs: DarwinBoolean) -> Bool {
-    return lhs.boolValue == rhs.boolValue
-  }
-}
-
-@_transparent
-public // COMPILER_INTRINSIC
-func _convertBoolToDarwinBoolean(_ x: Bool) -> DarwinBoolean {
-  return DarwinBoolean(x)
-}
-
-@_transparent
-public // COMPILER_INTRINSIC
-func _convertDarwinBooleanToBool(_ x: DarwinBoolean) -> Bool {
-  return x.boolValue
-}
-
-#endif
-
 //===----------------------------------------------------------------------===//
 // sys/errno.h
 //===----------------------------------------------------------------------===//
@@ -102,7 +31,7 @@ public var errno : Int32 {
 // stdio.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS) || os(FreeBSD) || os(PS4)
+#if os(FreeBSD) || os(PS4)
 public var stdin : UnsafeMutablePointer<FILE> {
   get {
     return __stdinp
@@ -250,9 +179,6 @@ public var S_IFBLK: mode_t  { return mode_t(0o060000) }
 public var S_IFREG: mode_t  { return mode_t(0o100000) }
 public var S_IFLNK: mode_t  { return mode_t(0o120000) }
 public var S_IFSOCK: mode_t { return mode_t(0o140000) }
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-public var S_IFWHT: mode_t  { return mode_t(0o160000) }
-#endif
 
 public var S_IRWXU: mode_t  { return mode_t(0o000700) }
 public var S_IRUSR: mode_t  { return mode_t(0o000400) }
@@ -272,13 +198,6 @@ public var S_IXOTH: mode_t  { return mode_t(0o000001) }
 public var S_ISUID: mode_t  { return mode_t(0o004000) }
 public var S_ISGID: mode_t  { return mode_t(0o002000) }
 public var S_ISVTX: mode_t  { return mode_t(0o001000) }
-
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
-public var S_ISTXT: mode_t  { return S_ISVTX }
-public var S_IREAD: mode_t  { return S_IRUSR }
-public var S_IWRITE: mode_t { return S_IWUSR }
-public var S_IEXEC: mode_t  { return S_IXUSR }
-#endif
 #endif
 
 //===----------------------------------------------------------------------===//
@@ -313,32 +232,11 @@ public func ioctl(
 // !os(Windows)
 #endif
 
-//===----------------------------------------------------------------------===//
-// unistd.h
-//===----------------------------------------------------------------------===//
-
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-@available(*, unavailable, message: "Please use threads or posix_spawn*()")
-public func fork() -> Int32 {
-  fatalError("unavailable function can't be called")
-}
-
-@available(*, unavailable, message: "Please use threads or posix_spawn*()")
-public func vfork() -> Int32 {
-  fatalError("unavailable function can't be called")
-}
-#endif
-
 //===----------------------------------------------------------------------===//
 // signal.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-public var SIG_DFL: sig_t? { return nil }
-public var SIG_IGN: sig_t { return unsafeBitCast(1, to: sig_t.self) }
-public var SIG_ERR: sig_t { return unsafeBitCast(-1, to: sig_t.self) }
-public var SIG_HOLD: sig_t { return unsafeBitCast(5, to: sig_t.self) }
-#elseif os(OpenBSD)
+#if os(OpenBSD)
 public var SIG_DFL: sig_t? { return nil }
 public var SIG_IGN: sig_t { return unsafeBitCast(1, to: sig_t.self) }
 public var SIG_ERR: sig_t { return unsafeBitCast(-1, to: sig_t.self) }
@@ -399,10 +297,7 @@ public typealias Semaphore = UnsafeMutablePointer<sem_t>
 
 /// The value returned by `sem_open()` in the case of failure.
 public var SEM_FAILED: Semaphore? {
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-  // The value is ABI.  Value verified to be correct for OS X, iOS, watchOS, tvOS.
-  return Semaphore(bitPattern: -1)
-#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(PS4) || os(Android) || os(Cygwin) || os(Haiku) || os(WASI)
+#if os(Linux) || os(FreeBSD) || os(OpenBSD) || os(PS4) || os(Android) || os(Cygwin) || os(Haiku) || os(WASI)
   // The value is ABI.  Value verified to be correct on Glibc.
   return Semaphore(bitPattern: 0)
 #else
@@ -432,7 +327,7 @@ public func sem_open(
 // time.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS) || os(Linux)
+#if os(Linux)
 
 @available(SwiftStdlib 5.7, *)
 extension timespec {
@@ -457,15 +352,9 @@ extension timeval {
   @available(SwiftStdlib 5.7, *)
   public init(_ duration: Duration) {
     let comps = duration.components
-#if os(Linux)
   // Linux platforms define timeval as Int/Int
   self.init(tv_sec: Int(comps.seconds),
               tv_usec: Int(comps.attoseconds / 1_000_000_000_000))
-#else
-    // Darwin platforms define timeval as Int/Int32
-    self.init(tv_sec: Int(comps.seconds),
-              tv_usec: Int32(comps.attoseconds / 1_000_000_000_000))
-#endif
   }
 }
 
@@ -485,7 +374,7 @@ extension Duration {
 
 // Some platforms don't have `extern char** environ` imported from C.
 #if SWIFT_STDLIB_HAS_ENVIRON
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS) || os(FreeBSD) || os(OpenBSD) || os(PS4)
+#if os(FreeBSD) || os(OpenBSD) || os(PS4)
 public var environ: UnsafeMutablePointer<UnsafeMutablePointer<CChar>?> {
   return _swift_stdlib_getEnviron()
 }
diff --git a/stdlib/public/Platform/README.md b/stdlib/public/Platform/README.md
index 5404201cf0701..d6845fc34b3c9 100644
--- a/stdlib/public/Platform/README.md
+++ b/stdlib/public/Platform/README.md
@@ -1,11 +1,10 @@
-This directory holds the Swift Standard Library's Darwin and Glibc Module,
-comprised of
+This directory holds the Swift Standard Library's Glibc Module, comprised of
 
 - The *overlay* library, which amends some APIs imported from Clang module.
-- Glibc only: The clang [module map] which specifies which headers need to
-  be imported from Glibc for bare minimum functionality.
+- The clang [module map] which specifies which headers need to be imported
+  from Glibc for bare minimum functionality.
 
-Note: On Darwin platforms, we assume clang [module map] is already installed
-in the system SDK.
+Note: Darwin platforms provide their own overlays and module maps in the
+system SDK.
 
 [module map]: http://clang.llvm.org/docs/Modules.html
diff --git a/stdlib/public/Platform/TiocConstants.swift b/stdlib/public/Platform/TiocConstants.swift
index 9510315d19908..d9df9acb4a2d4 100644
--- a/stdlib/public/Platform/TiocConstants.swift
+++ b/stdlib/public/Platform/TiocConstants.swift
@@ -10,10 +10,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Tty ioctl request constants, needed only on Darwin and FreeBSD.
+// Tty ioctl request constants, needed only on FreeBSD.
 
 // Constants available on all platforms, also available on Linux.
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS) || os(FreeBSD) || os(Haiku)
+#if os(FreeBSD) || os(Haiku)
 
 /// Set exclusive use of tty.
 public var TIOCEXCL: UInt { return 0x2000740d }
@@ -114,45 +114,6 @@ public var TIOCGLTC: UInt { return 0x40067474 }
 #endif
 
 
-// Darwin only constants, also available on Linux.
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
-
-/// Get termios struct.
-public var TIOCGETA: UInt { return 0x40487413 }
-/// Set termios struct.
-public var TIOCSETA: UInt { return 0x80487414 }
-/// Drain output, set.
-public var TIOCSETAW: UInt { return 0x80487415 }
-/// Drn out, fls in, set.
-public var TIOCSETAF: UInt { return 0x80487416 }
-/// Pty: generate signal.
-public var TIOCSIG: UInt { return 0x2000745f }
-/// Get modem control state.
-public var TIOCMODG: UInt { return 0x40047403 }
-/// Set modem control state.
-public var TIOCMODS: UInt { return 0x80047404 }
-/// Internal input VSTART.
-public var TIOCIXON: UInt { return 0x20007481 }
-/// Internal input VSTOP.
-public var TIOCIXOFF: UInt { return 0x20007480 }
-/// Remote input editing.
-public var TIOCREMOTE: UInt { return 0x80047469 }
-/// 4.2 compatibility.
-public var TIOCSCONS: UInt { return 0x20007463 }
-/// Enable/get timestamp of last DCd rise.
-public var TIOCDCDTIMESTAMP: UInt { return 0x40107458 }
-/// Download microcode to DSI Softmodem.
-public var TIOCDSIMICROCODE: UInt { return 0x20007455 }
-/// Grantpt(3).
-public var TIOCPTYGRANT: UInt { return 0x20007454 }
-/// Ptsname(3).
-public var TIOCPTYGNAME: UInt { return 0x40807453 }
-/// Unlockpt(3).
-public var TIOCPTYUNLK: UInt { return 0x20007452 }
-
-#endif
-
-
 // FreeBSD specific values and constants available only on FreeBSD.
 #if os(FreeBSD)
 
diff --git a/stdlib/public/Platform/tgmath.swift.gyb b/stdlib/public/Platform/tgmath.swift.gyb
index 1680044d4d59f..6983daf30a280 100644
--- a/stdlib/public/Platform/tgmath.swift.gyb
+++ b/stdlib/public/Platform/tgmath.swift.gyb
@@ -222,7 +222,7 @@ def TypedBinaryFunctions():
 // Note these do not have a corresponding LLVM intrinsic
 % for T, CT, f, ufunc in TypedUnaryFunctions():
 %  if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
+#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux)))
 %  end
 @_transparent
 public func ${ufunc}(_ x: ${T}) -> ${T} {
@@ -234,23 +234,6 @@ public func ${ufunc}(_ x: ${T}) -> ${T} {
 
 % end
 
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
-// Unary intrinsic functions
-// Note these have a corresponding LLVM intrinsic
-% for T, ufunc in TypedUnaryIntrinsicFunctions():
-%  if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
-%  end
-@_transparent
-public func ${ufunc}(_ x: ${T}) -> ${T} {
-  return _${ufunc}(x)
-}
-%  if T == 'Float80':
-#endif
-%  end
-
-% end
-#else
 // FIXME: As of now, we cannot declare 64-bit (Double/CDouble) overlays here.
 // Since CoreFoundation also exports libc functions, they will conflict with
 // Swift overlays when building Foundation. For now, just like normal
@@ -258,7 +241,7 @@ public func ${ufunc}(_ x: ${T}) -> ${T} {
 % for ufunc in UnaryIntrinsicFunctions:
 %  for T, CT, f in OverlayFloatTypes():
 %   if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
+#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux)))
 %   end
 @_transparent
 public func ${ufunc}(_ x: ${T}) -> ${T} {
@@ -269,13 +252,12 @@ public func ${ufunc}(_ x: ${T}) -> ${T} {
 %   end
 %  end
 % end
-#endif
 
 // Binary functions
 
 % for T, CT, f, bfunc in TypedBinaryFunctions():
 %  if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
+#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux)))
 %  end
 @_transparent
 public func ${bfunc}(_ lhs: ${T}, _ rhs: ${T}) -> ${T} {
@@ -290,7 +272,7 @@ public func ${bfunc}(_ lhs: ${T}, _ rhs: ${T}) -> ${T} {
 % # This is AllFloatTypes not OverlayFloatTypes because of the tuple return.
 % for T, CT, f in AllFloatTypes():
 %  if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || os(OpenBSD) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
+#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || os(OpenBSD) || ($Embedded && !os(Linux)))
 %  else:
 //  lgamma not available on Windows, apparently?
 #if !os(Windows)
@@ -308,7 +290,7 @@ public func lgamma(_ x: ${T}) -> (${T}, Int) {
 % # This is AllFloatTypes not OverlayFloatTypes because of the tuple return.
 % for T, CT, f in AllFloatTypes():
 %  if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
+#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux)))
 %  end
 @_transparent
 public func remquo(_ x: ${T}, _ y: ${T}) -> (${T}, Int) {
@@ -324,7 +306,7 @@ public func remquo(_ x: ${T}, _ y: ${T}) -> (${T}, Int) {
 
 % for T, CT, f in OverlayFloatTypes():
 %  if T == 'Float80':
-#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux) && !(os(macOS) || os(iOS) || os(watchOS) || os(tvOS))))
+#if (arch(i386) || arch(x86_64)) && !(os(Windows) || os(Android) || ($Embedded && !os(Linux)))
 %  end
 @available(swift, deprecated: 4.2/*, obsoleted: 5.1*/, message:
            "use ${T}(nan: ${T}.RawSignificand).")
diff --git a/stdlib/public/Synchronization/CMakeLists.txt b/stdlib/public/Synchronization/CMakeLists.txt
index 302d332b82c3e..b410bdf3fee92 100644
--- a/stdlib/public/Synchronization/CMakeLists.txt
+++ b/stdlib/public/Synchronization/CMakeLists.txt
@@ -37,18 +37,12 @@ set(SWIFT_SYNCHRONIZATION_GYB_SOURCES
 
 set(SWIFT_SYNCHRONIZATION_DARWIN_DEPENDENCIES)
 
-if(SWIFT_BUILD_SDK_OVERLAY)
-  set(SWIFT_SYNCHRONIZATION_DARWIN_DEPENDENCIES Darwin)
-endif()
-
 if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND SWIFT_SYNCHRONIZATION_DARWIN_DEPENDENCIES _Builtin_float)
 endif()
 
diff --git a/stdlib/public/libexec/swift-backtrace/CMakeLists.txt b/stdlib/public/libexec/swift-backtrace/CMakeLists.txt
index 8f42800b0e6f3..0c9c45b0b8fda 100644
--- a/stdlib/public/libexec/swift-backtrace/CMakeLists.txt
+++ b/stdlib/public/libexec/swift-backtrace/CMakeLists.txt
@@ -6,7 +6,6 @@ set(glibc)
 set(musl)
 
 if(SWIFT_BUILD_SDK_OVERLAY)
-  set(darwin Darwin)
   set(wincrt_sdk CRT WinSDK)
   set(glibc Glibc)
   set(musl Musl)
@@ -16,10 +15,8 @@ if((SWIFT_BUILD_CLANG_OVERLAYS
     OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
    AND (NOT DEFINED SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT
         OR NOT SWIFT_BUILD_CLANG_OVERLAYS_SKIP_BUILTIN_FLOAT))
-  # We need to make this dependency explicit because this library
-  # imports Darwin and Darwin re-exports _Builtin_float,
-  # but in most configurations we pull Darwin from the SDK,
-  # meaning we specify no Darwin dependency in the build system
+  # This library imports Darwin from the SDK, which re-exports
+  # _Builtin_float which is part of this build.
   list(APPEND darwin _Builtin_float)
 endif()