[cmake] Make include(GNUInstallDirs) always below project(..)

[Ericson2314]

Summary

Its defaulting logic must go after project(..) to work correctly, but project(..) is often in a standalone condition making this
awkward, since the rest of the condition code may also need GNUInstallDirs.

The good thing is there are the various standalone booleans, which I had missed before. This makes splitting the conditional blocks less awkward.

[Ericson2314]

Don't forget compiler-rt

[arichardson]

I believe LLVM_LIBDIR_SUFFIX was added as a workaround for not being able to use GNUInstallDirs (which will automatically detect the right suffixed e.g. for SuSE) in rG46fed3b475ddd92d02d9b72d0d77c5a939f132d1. Would it be possible to move the include() below the project()/enable_language() calls so that CMake can detect the expected libdir suffix and then use something like the following:

# If LLVM_LIBDIR_SUFFIX is defined, we use that to override the libdir, otherwise GNUInstallDirs defaults should be correct.
if(DEFINED LLVM_LIBDIR_SUFFIX)
  message(DEPRECATION "LLVM_LIBDIR_SUFFIX is deprecated, set CMAKE_INSTALL_LIBDIR to lib${LLVM_LIBDIR_SUFFIX} instead")
  set(CMAKE_INSTALL_LIBDIR lib${LLVM_LIBDIR_SUFFIX})
endif()
include(GNUInstallDirs)

[arichardson]

I can't see anywhere where the GNUInstallDirs variables are used before project(), so can't we just move the includes further down?

[arichardson]

I see AddLLVM already includes GNUInstallDirs, can we add the LLVM_LIBDIR_SUFFIX check to that file and avoid including GNUInstallDirs explicitly in all the projects? The standalone builds will pull in GNUInstallDirs via AddLLVM, and the non-standalone builds should already have the variables defined?

[Ericson2314]

In D117639#3254065, @arichardson wrote:

I believe LLVM_LIBDIR_SUFFIX was added as a workaround for not being able to use GNUInstallDirs (which will automatically detect the right suffixed e.g. for SuSE) in rG46fed3b475ddd92d02d9b72d0d77c5a939f132d1. Would it be possible to move the include() below the project()/enable_language() calls so that CMake can detect the expected libdir suffix and then use something like the following:

# If LLVM_LIBDIR_SUFFIX is defined, we use that to override the libdir, otherwise GNUInstallDirs defaults should be correct.
if(DEFINED LLVM_LIBDIR_SUFFIX)
  message(DEPRECATION "LLVM_LIBDIR_SUFFIX is deprecated, set CMAKE_INSTALL_LIBDIR to lib${LLVM_LIBDIR_SUFFIX} instead")
  set(CMAKE_INSTALL_LIBDIR lib${LLVM_LIBDIR_SUFFIX})
endif()
include(GNUInstallDirs)

I would love to do this, but I was unsure whether that was acceptable.

It gets even more complicated downstream when other *_LIBDIR_SUFFIX variable are defaulted from LLVM_LIBDIR_SUFFIX. Can we deprecate that too?

[Ericson2314]

Just move them

@arichardson as the description now indicates, I found the STANDALONE variables, which made doing what was originally asked less awkard than I feared.

I do also prefer splitting the blocks to putting the logic further below. as I rather not get clever with questions of "does this include transitively reference gnu install dirs?" etc.

[Ericson2314]

Rebase after D117617 landed

[arichardson]

This LGTM, but please wait for someone else to review before committing it.

lldb/CMakeLists.txt

20

Could keep this in the first if then you won't have to duplicate setting LLDB_BUILT_STANDALONE?

[beanz]

LGTM.

[phosek]

LGTM

flang/CMakeLists.txt

 cmake_minimum_required(VERSION 3.13.4)
 
 set(CMAKE_BUILD_WITH_INSTALL_NAME_DIR ON)
 
 # Flang requires C++17.
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 set(FLANG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE)
   message(FATAL_ERROR "In-source builds are not allowed. \
           Please create a directory and run cmake from there,\
           passing the path to this source directory as the last argument.\

libcxx/CMakeLists.txt

 # See https://libcxx.llvm.org/docs/BuildingLibcxx.html for instructions on how
 # to build libcxx with CMake.
 
 if (NOT IS_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/../libcxxabi")
   message(FATAL_ERROR "libc++ now requires being built in a monorepo layout with libcxxabi available")
 endif()
 
 #===============================================================================
 # Setup Project
 #===============================================================================
 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"

libcxxabi/CMakeLists.txt

 # See www/CMake.html for instructions on how to build libcxxabi with CMake.
 
 if (NOT IS_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/../libcxx")
   message(FATAL_ERROR "libc++abi now requires being built in a monorepo layout with libcxx available")
 endif()
 
 #===============================================================================
 # Setup Project
 #===============================================================================
 
 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"

libunwind/CMakeLists.txt

 if (NOT IS_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/../libcxx")
   message(FATAL_ERROR "libunwind requires being built in a monorepo layout with libcxx available")
 endif()
 
 #===============================================================================
 # Setup Project
 #===============================================================================
 
 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"

lld/CMakeLists.txt

 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 # If we are not building as a part of LLVM, build LLD as an
 # standalone project, using LLVM as an external library:
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(lld)
 
   set(CMAKE_INCLUDE_CURRENT_DIR ON)

lldb/CMakeLists.txt

 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 # Add path for custom modules.
 set(CMAKE_MODULE_PATH
   ${CMAKE_MODULE_PATH}
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
   )
 
 # If we are not building as part of LLVM, build LLDB as a standalone project,
 # using LLVM as an external library.
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(lldb)
   include(LLDBStandalone)
 
   set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)
   set(CMAKE_CXX_EXTENSIONS NO)
 endif()
 
 include(LLDBConfig)
 include(AddLLDB)

llvm/CMakeLists.txt

 # See docs/CMake.html for instructions about how to build LLVM with CMake.
 
 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 # CMP0116: Ninja generators transform `DEPFILE`s from `add_custom_command()`
 # New in CMake 3.20. https://cmake.org/cmake/help/latest/policy/CMP0116.html
 if(POLICY CMP0116)
   cmake_policy(SET CMP0116 OLD)
 endif()
 

polly/CMakeLists.txt

+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 # Check if this is a in tree build.
 if (NOT DEFINED LLVM_MAIN_SRC_DIR)
   project(Polly)
   cmake_minimum_required(VERSION 3.13.4)
 
   # Where is LLVM installed?

pstl/CMakeLists.txt

 #===-- CMakeLists.txt ----------------------------------------------------===##
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===----------------------------------------------------------------------===##
 cmake_minimum_required(VERSION 3.13.4)
 
+if(NOT DEFINED CMAKE_INSTALL_LIBDIR)
+  # No suffixes by default: LLVM does those separately.
+  set(CMAKE_INSTALL_LIBDIR lib)
+endif()
 include(GNUInstallDirs)
 
 set(PARALLELSTL_VERSION_FILE "${CMAKE_CURRENT_SOURCE_DIR}/include/pstl/internal/pstl_config.h")
 file(STRINGS "${PARALLELSTL_VERSION_FILE}" PARALLELSTL_VERSION_SOURCE REGEX "#define _PSTL_VERSION .*$")
 string(REGEX REPLACE "#define _PSTL_VERSION (.*)$" "\\1" PARALLELSTL_VERSION_SOURCE "${PARALLELSTL_VERSION_SOURCE}")
 math(EXPR VERSION_MAJOR "(${PARALLELSTL_VERSION_SOURCE} / 1000)")
 math(EXPR VERSION_MINOR "((${PARALLELSTL_VERSION_SOURCE} % 1000) / 10)")
 math(EXPR VERSION_PATCH "(${PARALLELSTL_VERSION_SOURCE} % 10)")