Add gold linker support for Swift executables and shared libraries on…

… Linux.

This skips the Swift standard library due to the linker script incompatibility
issue.

As before for other related projects, the build-script-impl option
'--use-gold-linker' triggers usage of this.


Swift SVN r32706

CMakeLists.txt

@@ -71,6 +71,11 @@ set(SWIFT_VENDOR "" CACHE STRING
 set(SWIFT_COMPILER_VERSION "" CACHE STRING
     "The internal version of the Swift compiler")
 
+# Indicate whether Swift should attempt to use the gold linker.
+# This is not used on Darwin.
+set(SWIFT_ENABLE_GOLD_LINKER FALSE CACHE BOOL
+    "Enable using the gold linker when available")
+
 set(_SWIFT_KNOWN_INSTALL_COMPONENTS
     "compiler;clang-builtin-headers;clang-resource-dir-symlink;clang-builtin-headers-in-clang-resource-dir;arclite-symlink;stdlib;stdlib-experimental;sdk-overlay;editor-integration;lang-docs;tools;testsuite-tools;dev")
 

cmake/modules/AddSwift.cmake

@@ -1037,6 +1037,18 @@ function(_add_swift_library_single target name)
       ${SWIFTLIB_SINGLE_USE_INTERNAL_SDK}
       link_flags)
 
+  # Handle gold linker flags for shared libraries.
+  if(SWIFT_ENABLE_GOLD_LINKER AND SWIFTLIB_SINGLE_SHARED)
+    if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "LINUX")
+      # Extend the link_flags for the gold linker so long as this
+      # isn't the standard library.  The standard library uses a
+      # linker script that isn't supported by the gold linker.
+      if(NOT SWIFTLIB_SINGLE_IS_STDLIB)
+        list(APPEND link_flags "-fuse-ld=gold")
+      endif()
+    endif()
+  endif()
+
   # Configure plist creation for OS X.
   set(PLIST_INFO_PLIST "Info.plist" CACHE STRING "Plist name")
   if(APPLE AND SWIFTLIB_SINGLE_IS_STDLIB)
@@ -1622,6 +1634,12 @@ function(_add_swift_executable_single name)
         "-Xlinker" "@executable_path/../lib/swift/${SWIFT_SDK_${SWIFTEXE_SINGLE_SDK}_LIB_SUBDIR}")
   endif()
 
+  if(SWIFT_ENABLE_GOLD_LINKER AND
+     ( "${SWIFTEXE_SINGLE_SDK}" STREQUAL "LINUX" ) )
+    # Extend the link_flags for the gold linker.
+    list(APPEND link_flags "-fuse-ld=gold")
+  endif()
+
   # Find the names of dependency library targets.
   #
   # We don't add the ${ARCH} to the target suffix because we want to link