Merge branch 'use-mold'

Use (faster) mold linker for the CI builds and, optionally, for the
local ones.

See #1106.

CMakeLists.txt

@@ -19,6 +19,12 @@ if(NOT DEFINED CMAKE_CXX_STANDARD OR CMAKE_CXX_STANDARD LESS 14)
 endif()
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
+# Path to additional CMake modules
+set(CMAKE_MODULE_PATH ${SOCI_SOURCE_DIR}/cmake/modules ${CMAKE_MODULE_PATH})
+set(CMAKE_MODULE_PATH ${SOCI_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH})
+
+include(SociUtilities)
+
 ###############################################################################
 # Build features and variants
 ##############################################################################
@@ -47,13 +53,7 @@ if (SOCI_LTO)
 
         if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
             # Check for lld as clang lto works best with its own linker
-            include(CheckCXXCompilerFlag)
-            check_cxx_compiler_flag("-fuse-ld=lld" HAS_LLD)
-            if (HAS_LLD)
-                SET(CMAKE_EXE_LINKER_FLAGS  "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=lld")
-                SET(CMAKE_SHARED_LINKER_FLAGS  "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=lld")
-                SET(CMAKE_MODULE_LINKER_FLAGS  "${CMAKE_MODULE_LINKER_FLAGS} -fuse-ld=lld")
-            endif()
+            soci_use_ld_if_supported(lld)
         endif()
     elseif(supported)
         message(STATUS "IPO / LTO is supported but conflicts with ASAN and not enabled")
@@ -82,15 +82,20 @@ else()
     set(SOCI_HAVE_VISIBILITY_SUPPORT off)
 endif()
 
-###############################################################################
-# SOCI CMake modules
-###############################################################################
+# Allow using alternative linker such as mold, which can be significantly
+# faster than GNU ld.
+option(SOCI_LD "Use non-default linker, such as 'mold'" "")
+if(SOCI_LD)
+	# -fuse-ld works only with recent gcc (>= 12), but we don't need to support
+	# this with all gcc versions as this is entirely optional. I.e. if we really
+	# wanted to, we could use -B option as explained in mold README to make it
+	# work with any gcc, but for now keep the things simple.
+	soci_use_ld_if_supported(${SOCI_LD})
+endif()
 
-# Path to additional CMake modules
-set(CMAKE_MODULE_PATH ${SOCI_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH})
-set(CMAKE_MODULE_PATH ${SOCI_SOURCE_DIR}/cmake/modules ${CMAKE_MODULE_PATH})
-
-include(SociUtilities)
+###############################################################################
+# SOCI configuration
+###############################################################################
 include(SociConfig)
 
 colormsg(_HIBLUE_ "Configuring SOCI:")

cmake/SociUtilities.cmake

@@ -424,3 +424,13 @@ function(soci_target_output_name TARGET_NAME OUTPUT_NAME)
 
   set(${OUTPUT_NAME} ${TARGET_NAME}${SUFFIX} PARENT_SCOPE)
 endfunction()
+
+# Check if the given linker is supported and use it if it is.
+function(soci_use_ld_if_supported ld)
+    include(CheckCXXCompilerFlag)
+    set(ld_flag "-fuse-ld=${ld}")
+    check_cxx_compiler_flag(${ld_flag} can_use_ld)
+    if (can_use_ld)
+        add_link_options(${ld_flag})
+    endif()
+endfunction()

scripts/ci/install.sh

@@ -40,6 +40,11 @@ case "$(uname)" in
 
         run_apt update
         run_apt install ${packages_to_install}
+
+        # Get mold and replace the default linker with it.
+        wget --quiet -O- https://github.com/rui314/mold/releases/download/v2.4.0/mold-2.4.0-$(uname -m)-linux.tar.gz | \
+          tar -C /usr/local --strip-components=1 -xzf -
+        ln -sf /usr/local/bin/mold /usr/bin/ld
         ;;
 
     FreeBSD)