When building stdlib, pass -prespecialize-generic-metadata from CMake, and respect the flag in IRGenModule::shouldPrespecializeGenericMetadata (#38946)

Author: kubamracek

lib/IRGen/IRGenModule.cpp

@@ -1702,7 +1702,7 @@ bool IRGenModule::shouldPrespecializeGenericMetadata() {
       (Triple.isOSDarwin() ||
        (Triple.isOSLinux() && !(Triple.isARM() && Triple.isArch32Bit())));
   if (canPrespecializeTarget && isStandardLibrary()) {
-    return true;
+    return IRGen.Opts.PrespecializeGenericMetadata;
   }
   auto &context = getSwiftModule()->getASTContext();
   auto deploymentAvailability =

stdlib/CMakeLists.txt

@@ -44,6 +44,14 @@ else()
   set(SWIFT_BUILD_TEST_SUPPORT_MODULES_default FALSE)
 endif()
 
+if("${SWIFT_HOST_VARIANT_SDK}" MATCHES "(OSX|IOS*|TVOS*|WATCHOS*)")
+  set(SWIFT_STDLIB_ENABLE_PRESPECIALIZATION_default TRUE)
+elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "LINUX")
+  set(SWIFT_STDLIB_ENABLE_PRESPECIALIZATION_default TRUE)
+else()
+  set(SWIFT_STDLIB_ENABLE_PRESPECIALIZATION_default FALSE)
+endif()
+
 #
 # User-configurable options for the standard library.
 #
@@ -82,6 +90,10 @@ option(SWIFT_BUILD_TEST_SUPPORT_MODULES
 option(SWIFT_FREESTANDING_FLAVOR
        "When building the FREESTANDING stdlib, which build style to use (options: apple, linux)")
 
+option(SWIFT_STDLIB_ENABLE_PRESPECIALIZATION
+       "Should stdlib be built with generic metadata prespecialization enabled. Defaults to On on Darwin and on "
+       "${SWIFT_STDLIB_ENABLE_PRESPECIALIZATION_default}")
+
 set(SWIFT_STDLIB_ENABLE_LTO OFF CACHE STRING "Build Swift stdlib with LTO. One
     must specify the form of LTO by setting this to one of: 'full', 'thin'. This
     option only affects the standard library and runtime, not tools.")

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -1673,6 +1673,10 @@ function(add_swift_target_library name)
                       "-Xfrontend;-disable-implicit-distributed-module-import")
   endif()
 
+  if(SWIFTLIB_IS_STDLIB AND SWIFT_STDLIB_ENABLE_PRESPECIALIZATION)
+    list(APPEND SWIFTLIB_SWIFT_COMPILE_FLAGS "-Xfrontend;-prespecialize-generic-metadata")
+  endif()
+
   # If we are building this library for targets, loop through the various
   # SDKs building the variants of this library.
   list_intersect(

utils/build-presets.ini

@@ -2433,7 +2433,10 @@ swift-enable-compatibility-overrides=0
 swift-runtime-macho-no-dyld=1
 swift-stdlib-single-threaded-runtime=1
 swift-stdlib-os-versioning=0
-extra-cmake-options=-DSWIFT_ENABLE_DISPATCH:BOOL=FALSE -DSWIFT_IMPLICIT_CONCURRENCY_IMPORT:BOOL=FALSE
+extra-cmake-options=
+    -DSWIFT_ENABLE_DISPATCH:BOOL=FALSE
+    -DSWIFT_IMPLICIT_CONCURRENCY_IMPORT:BOOL=FALSE
+    -DSWIFT_STDLIB_ENABLE_PRESPECIALIZATION:BOOL=FALSE
 
 [preset: stdlib_S_standalone_minimal_macho_x86_64,build]
 mixin-preset=