[Clang][LLD][cmake] Drop deprecated support for `llvm-config`-based build

[Ericson2314]

Summary

This has been deprecated for Clang since D51714 (2018), and LLD since
D116492 (earlier in 2022).

That means both methods have been deprecated for at least two releases
(14 and 15), and Clang may more.

Not sure what the deprecation policy is, but I am opening this now for
whenever it's OK to land.

[compnerd]

Since it has been deprecated for 2 releases, it seems reasonable to cleanup. This seems good to me from the build side, please do wait a bit for anyone else to chime in on this.

[phosek]

LGTM we should consider removing llvm-config from other subprojects as a follow up cleanup.

[Ericson2314]

Should I wait for anyone else / do something like announcing this on discourse?

It looks like the only other use case is libclc, which sadly only supports the old way so we will need to do another deprecation cycle I'd think for it.

[tstellar]

In D130735#3691016, @Ericson2314 wrote:

Should I wait for anyone else / do something like announcing this on discourse?

It looks like the only other use case is libclc, which sadly only supports the old way so we will need to do another deprecation cycle I'd think for it.

I think it is fine to drop it from libclc without deprecating it.

[tstellar]

LGTM. I just tested this patch in our build config and it works fine.

[Ericson2314]

Abandoing based on @phosek's point in D128777 about it being nice to have it easy to revert them individually.

clang/CMakeLists.txt

 # Must go below project(..)
 include(GNUInstallDirs)
 
 if(CLANG_BUILT_STANDALONE)
   set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)
   set(CMAKE_CXX_EXTENSIONS NO)
 
-  # Rely on llvm-config.
-  set(LLVM_CONFIG_OUTPUT)
-  if(LLVM_CONFIG)
-    set (LLVM_CONFIG_FOUND 1)
-    message(STATUS "Found LLVM_CONFIG as ${LLVM_CONFIG}")
-    message(DEPRECATION "Using llvm-config to detect the LLVM installation is \
-          deprecated.  The installed cmake files should be used \
-          instead.  CMake should be able to detect your LLVM install \
-          automatically, but you can also use LLVM_DIR to specify \
-          the path containing LLVMConfig.cmake.")
-    set(CONFIG_COMMAND ${LLVM_CONFIG}
-      "--includedir"
-      "--prefix"
-      "--src-root"
-      "--cmakedir"
-      "--bindir"
-      "--libdir"
-      "--assertion-mode"
-      )
-    execute_process(
-      COMMAND ${CONFIG_COMMAND}
-      RESULT_VARIABLE HAD_ERROR
-      OUTPUT_VARIABLE LLVM_CONFIG_OUTPUT
-    )
-    if(NOT HAD_ERROR)
-      string(REGEX REPLACE
-        "[ \t]*[\r\n]+[ \t]*" ";"
-        LLVM_CONFIG_OUTPUT ${LLVM_CONFIG_OUTPUT})
-    else()
-      string(REPLACE ";" " " CONFIG_COMMAND_STR "${CONFIG_COMMAND}")
-      message(STATUS "${CONFIG_COMMAND_STR}")
-      message(FATAL_ERROR "llvm-config failed with status ${HAD_ERROR}")
-    endif()
-
-    list(GET LLVM_CONFIG_OUTPUT 0 MAIN_INCLUDE_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 1 LLVM_OBJ_ROOT)
-    list(GET LLVM_CONFIG_OUTPUT 2 MAIN_SRC_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 3 LLVM_CONFIG_CMAKE_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 4 TOOLS_BINARY_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 5 LIBRARY_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 6 ENABLE_ASSERTIONS)
-
-    # Normalize LLVM_CMAKE_DIR. --cmakedir might contain backslashes.
-    # CMake assumes slashes as PATH.
-    file(TO_CMAKE_PATH ${LLVM_CONFIG_CMAKE_DIR} LLVM_CMAKE_DIR)
-  endif()
-
-
   if(NOT MSVC_IDE)
     set(LLVM_ENABLE_ASSERTIONS ${ENABLE_ASSERTIONS}
       CACHE BOOL "Enable assertions")
     # Assertions should follow llvm-config's.
     mark_as_advanced(LLVM_ENABLE_ASSERTIONS)
   endif()
 
   find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_DIR}")
   list(APPEND CMAKE_MODULE_PATH "${LLVM_DIR}")
 
-  # We can't check LLVM_CONFIG here, because find_package(LLVM ...) also sets
-  # LLVM_CONFIG.
-  if (NOT LLVM_CONFIG_FOUND)
-    # Pull values from LLVMConfig.cmake.  We can drop this once the llvm-config
-    # path is removed.
-    set(INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
-    set(LLVM_OBJ_DIR "${LLVM_BINARY_DIR}")
-    # N.B. this is just a default value, the CACHE PATHs below can be overriden.
-    set(MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm")
-    set(TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}")
-    set(LIBRARY_DIR "${LLVM_LIBRARY_DIR}")
-  else()
-    set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
-  endif()
-
-  set(LLVM_INCLUDE_DIRS ${INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
-  set(LLVM_BINARY_DIR "${LLVM_OBJ_ROOT}" CACHE PATH "Path to LLVM build tree")
-  set(LLVM_MAIN_SRC_DIR "${MAIN_SRC_DIR}" CACHE PATH "Path to LLVM source tree")
-  set(LLVM_TOOLS_BINARY_DIR "${TOOLS_BINARY_DIR}" CACHE PATH "Path to llvm/bin")
-  set(LLVM_LIBRARY_DIR "${LIBRARY_DIR}" CACHE PATH "Path to llvm/lib")
+  # Turn into CACHE PATHs for overwritting
+  set(LLVM_INCLUDE_DIRS ${LLVM_INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
+  set(LLVM_BINARY_DIR "${LLVM_BINARY_DIR}" CACHE PATH "Path to LLVM build tree")
+  set(LLVM_MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm" CACHE PATH "Path to LLVM source tree")
+  set(LLVM_TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}" CACHE PATH "Path to llvm/bin")
+  set(LLVM_LIBRARY_DIR "${LLVM_LIBRARY_DIR}" CACHE PATH "Path to llvm/lib")
 
   find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)
 
   # They are used as destination of target generators.
   set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
   set(LLVM_LIBRARY_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
   if(WIN32 OR CYGWIN)
if (CLANG_ENABLE_BOOTSTRAP)
   # otherwise it defaults the linker to be link.exe.
   if(BOOTSTRAP_LLVM_ENABLE_LLD)
     if((WIN32 AND NOT BOOTSTRAP_CMAKE_SYSTEM_NAME) OR BOOTSTRAP_CMAKE_SYSTEM_NAME STREQUAL "Windows")
       set(${CLANG_STAGE}_LINKER -DCMAKE_LINKER=${LLVM_RUNTIME_OUTPUT_INTDIR}/lld-link${CMAKE_EXECUTABLE_SUFFIX})
     endif()
   endif()
 
   if(BOOTSTRAP_CMAKE_SYSTEM_NAME)
-    set(${CLANG_STAGE}_CONFIG -DLLVM_CONFIG_PATH=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-config)
     set(${CLANG_STAGE}_TABLEGEN
       -DLLVM_TABLEGEN=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-tblgen
       -DCLANG_TABLEGEN=${LLVM_RUNTIME_OUTPUT_INTDIR}/clang-tblgen)
     if(BOOTSTRAP_CMAKE_SYSTEM_NAME STREQUAL "Linux")
       if(BOOTSTRAP_LLVM_ENABLE_LLD)
         set(${CLANG_STAGE}_LINKER -DCMAKE_LINKER=${LLVM_RUNTIME_OUTPUT_INTDIR}/ld.lld)
       endif()
       if(NOT BOOTSTRAP_LLVM_ENABLE_LTO)
ExternalProject_Add(${NEXT_CLANG_STAGE}
     CMAKE_ARGS
                 # We shouldn't need to set this here, but INSTALL_DIR doesn't
                 # seem to work, so instead I'm passing this through
                 -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
                 ${PASSTHROUGH_VARIABLES}
                 ${CLANG_BOOTSTRAP_CMAKE_ARGS}
                  -DCLANG_STAGE=${NEXT_CLANG_STAGE}
                 ${COMPILER_OPTIONS}
-                ${${CLANG_STAGE}_CONFIG}
                 ${${CLANG_STAGE}_TABLEGEN}
                 ${LTO_LIBRARY} ${verbose} ${PGO_OPT}
                 ${${CLANG_STAGE}_LINKER}
                 ${${CLANG_STAGE}_AR}
                 ${${CLANG_STAGE}_RANLIB}
                 ${${CLANG_STAGE}_OBJCOPY}
                 ${${CLANG_STAGE}_STRIP}
     INSTALL_COMMAND ""

lld/CMakeLists.txt

 
 if(LLD_BUILT_STANDALONE)
   set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)
   set(CMAKE_CXX_EXTENSIONS NO)
 
   set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
-  # Rely on llvm-config.
-  set(LLVM_CONFIG_OUTPUT)
-  if(NOT LLVM_CONFIG)
-   # back compat
-   set(LLVM_CONFIG "${LLVM_CONFIG_PATH}")
-  endif()
-  if(LLVM_CONFIG)
-    set (LLVM_CONFIG_FOUND 1)
-    message(STATUS "Found LLVM_CONFIG as ${LLVM_CONFIG}")
-    message(DEPRECATION "Using llvm-config to detect the LLVM installation is \
-          deprecated.  The installed cmake files should be used \
-          instead.  CMake should be able to detect your LLVM install \
-          automatically, but you can also use LLVM_DIR to specify \
-          the path containing LLVMConfig.cmake.")
-    set(CONFIG_COMMAND ${LLVM_CONFIG}
-      "--includedir"
-      "--prefix"
-      "--src-root"
-      "--cmakedir"
-      )
-    execute_process(
-      COMMAND ${CONFIG_COMMAND}
-      RESULT_VARIABLE HAD_ERROR
-      OUTPUT_VARIABLE LLVM_CONFIG_OUTPUT
-    )
-    if(NOT HAD_ERROR)
-      string(REGEX REPLACE
-        "[ \t]*[\r\n]+[ \t]*" ";"
-        LLVM_CONFIG_OUTPUT ${LLVM_CONFIG_OUTPUT})
-    else()
-      string(REPLACE ";" " " CONFIG_COMMAND_STR "${CONFIG_COMMAND}")
-      message(STATUS "${CONFIG_COMMAND_STR}")
-      message(FATAL_ERROR "llvm-config failed with status ${HAD_ERROR}")
-    endif()
-
-    list(GET LLVM_CONFIG_OUTPUT 0 MAIN_INCLUDE_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 1 LLVM_OBJ_ROOT)
-    list(GET LLVM_CONFIG_OUTPUT 2 MAIN_SRC_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 3 LLVM_CONFIG_CMAKE_DIR)
-
-    # Normalize LLVM_CMAKE_DIR. --cmakedir might contain backslashes.
-    # CMake assumes slashes as PATH.
-    file(TO_CMAKE_PATH ${LLVM_CONFIG_CMAKE_DIR} LLVM_CMAKE_DIR)
-  endif()
-
   find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_DIR}")
   list(APPEND CMAKE_MODULE_PATH "${LLVM_DIR}")
 
-  # We can't check LLVM_CONFIG here, because find_package(LLVM ...) also sets
-  # LLVM_CONFIG.
-  if (NOT LLVM_CONFIG_FOUND)
-    # Pull values from LLVMConfig.cmake.  We can drop this once the llvm-config
-    # path is removed.
-    set(INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
-    set(LLVM_OBJ_DIR "${LLVM_BINARY_DIR}")
-    # N.B. this is just a default value, the CACHE PATHs below can be overridden.
-    set(MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm")
-  else()
-    set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
-  endif()
-
-  set(LLVM_INCLUDE_DIRS ${INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
-  set(LLVM_BINARY_DIR "${LLVM_OBJ_ROOT}" CACHE PATH "Path to LLVM build tree")
-  set(LLVM_MAIN_SRC_DIR "${MAIN_SRC_DIR}" CACHE PATH "Path to LLVM source tree")
+  # Turn into CACHE PATHs for overwritting
+  set(LLVM_INCLUDE_DIRS ${LLVM_INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
+  set(LLVM_BINARY_DIR "${LLVM_BINARY_DIR}" CACHE PATH "Path to LLVM build tree")
+  set(LLVM_MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm" CACHE PATH "Path to LLVM source tree")
 
   find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)
 
   # They are used as destination of target generators.
   set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
   set(LLVM_LIBRARY_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})