Fix LTO on newer macOS. (ldc-developers#4548)

The trouble was that the libLTO-ldc.dylib was not used by ld64, even though it is explicitly passed using -lto_library. Somehow the library renaming (adding "-ldc" postfix) is not working properly. I did not figure out how to fix it (the usual install-name-tool and resigning did not work), the only fix that worked is to not rename it at all.
This bug went unnoticed because at -O0, there is no LTO object file output at all; hence the -O3 addition to the thinlto testcase.

CMakeLists.txt

@@ -753,6 +753,23 @@ function(copy_and_rename_file source_path target_path)
     file(RENAME ${target_dir}/${source_name} ${target_path})
 endfunction()
 
+
+function(copy_and_install_llvm_library llvm_lib_path ldc_lib_name fixup_dylib)
+        set(ldc_lib_path ${PROJECT_BINARY_DIR}/lib${LIB_SUFFIX}/${ldc_lib_name})
+        copy_and_rename_file(${llvm_lib_path} ${ldc_lib_path})
+        if (APPLE AND fixup_dylib)
+            execute_process(COMMAND install_name_tool -id @rpath/${ldc_lib_name} ${ldc_lib_path} ERROR_VARIABLE INSTALL_NAME_TOOL_STDERR)
+            if(${INSTALL_NAME_TOOL_STDERR} MATCHES "warning: changes being made to the file will invalidate the code signature")
+                # Eat the warning, it's ok.
+            elseif("${INSTALL_NAME_TOOL_STDERR}" STREQUAL "")
+            else()
+                message(WARNING "install_name_tool stderr: ${INSTALL_NAME_TOOL_STDERR}")
+            endif()
+            execute_process(COMMAND codesign --force -s - ${ldc_lib_path})
+        endif()
+        install(FILES ${ldc_lib_path} DESTINATION ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX})
+endfunction()
+
 #
 # Locate LLVM's LTO binary and use it
 #
@@ -765,15 +782,14 @@ set(LDC_INSTALL_LTOPLUGIN ${LDC_INSTALL_LTOPLUGIN_DEFAULT} CACHE BOOL "Copy/inst
 if (LDC_INSTALL_LTOPLUGIN)
     if(APPLE)
         set(LLVM_LTO_BINARY ${LLVM_LIBRARY_DIRS}/libLTO.dylib)
-        set(LDC_LTO_BINARY_NAME libLTO-ldc.dylib)
+        set(LDC_LTO_BINARY_NAME libLTO.dylib)
     elseif(UNIX)
         set(LLVM_LTO_BINARY ${LLVM_LIBRARY_DIRS}/LLVMgold.so)
         set(LDC_LTO_BINARY_NAME LLVMgold-ldc.so)
     endif()
     if(EXISTS ${LLVM_LTO_BINARY})
         message(STATUS "-- Including LTO linker plugin (LDC_INSTALL_LTOPLUGIN): ON (${LLVM_LTO_BINARY})")
-        copy_and_rename_file(${LLVM_LTO_BINARY} ${PROJECT_BINARY_DIR}/lib${LIB_SUFFIX}/${LDC_LTO_BINARY_NAME})
-        install(PROGRAMS ${PROJECT_BINARY_DIR}/lib${LIB_SUFFIX}/${LDC_LTO_BINARY_NAME} DESTINATION ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX})
+        copy_and_install_llvm_library(${LLVM_LTO_BINARY} ${LDC_LTO_BINARY_NAME} TRUE)
     else()
         message(STATUS "-- Including LTO linker plugin (LDC_INSTALL_LTOPLUGIN): OFF (cannot find ${LLVM_LTO_BINARY})")
     endif()
@@ -799,18 +815,7 @@ function(copy_compilerrt_lib llvm_lib_name ldc_lib_name fixup_dylib)
     endif()
     if(EXISTS ${llvm_lib_path})
         message(STATUS "--  - ${llvm_lib_path} --> ${ldc_lib_name}")
-        set(ldc_lib_path ${PROJECT_BINARY_DIR}/lib${LIB_SUFFIX}/${ldc_lib_name})
-        copy_and_rename_file(${llvm_lib_path} ${ldc_lib_path})
-        if (fixup_dylib)
-            execute_process(COMMAND install_name_tool -id @rpath/${ldc_lib_name} ${ldc_lib_path} ERROR_VARIABLE INSTALL_NAME_TOOL_STDERR)
-            if(${INSTALL_NAME_TOOL_STDERR} MATCHES "warning: changes being made to the file will invalidate the code signature")
-                # Eat the warning, it's ok.
-            else()
-                message(WARNING "install_name_tool stderr: ${INSTALL_NAME_TOOL_STDERR}")
-            endif()
-            execute_process(COMMAND codesign --force -s - ${ldc_lib_path})
-        endif()
-        install(FILES ${ldc_lib_path} DESTINATION ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX})
+        copy_and_install_llvm_library(${llvm_lib_path} ${ldc_lib_name} ${fixup_dylib})
     else()
         message(STATUS "--  - not found: ${llvm_lib_path}")
     endif()

driver/linker-gcc.cpp

@@ -172,8 +172,8 @@ std::string getLTOdylibPath() {
     error(Loc(), "-flto-binary: '%s' not found", ltoLibrary.c_str());
     fatal();
   } else {
-    // The plugin packaged with LDC has a "-ldc" suffix.
-    std::string searchPath = exe_path::prependLibDir("libLTO-ldc.dylib");
+    // Give priority to the plugin packaged with LDC.
+    std::string searchPath = exe_path::prependLibDir("libLTO.dylib");
     if (llvm::sys::fs::exists(searchPath))
       return searchPath;
 

tests/linking/thinlto_1.d

@@ -3,7 +3,7 @@
 // REQUIRES: LTO
 
 // RUN: %ldc %s -of=%t%obj -c -flto=thin -vv | FileCheck %s
-// RUN: %ldc -flto=thin -run %s
+// RUN: %ldc -flto=thin -O3 -run %s
 
 // CHECK: Writing LLVM bitcode
 // CHECK: Creating module summary for ThinLTO