[llvm] [cmake] Move LLVM_INSTALL_PACKAGE_DIR top-level to fix llvm-config

[mgorny]

Summary

Move the LLVM_INSTALL_PACKAGE_DIR declaration from llvm/cmake/modules
directory to the top-level llvm/CMakeLists.txt, in order to fix
the regression in llvm-config --cmakedir output for installed LLVM.
Since the tools directory is processed by CMake prior to
llvm/cmake/modules, the llvm-config executable ended up using
the variable prior to it being defined and incorrectly used an empty
path, resulting in e.g.:

$ llvm-config --cmakedir
/usr/lib/llvm/16/

With this patch, the path is defined (and therefore the default value
is being set) prior to adding the tools subdirectory and llvm-config
starts working correctly:

$ llvm-config --cmakedir
/usr/lib/llvm/16/lib64/cmake/llvm

This fixes a regression introduced by D130539. Thanks to Petr Polezhaev
for reporting the problem @ https://bugs.gentoo.org/865165

[Ericson2314]

Can we add comment saying why it is this way? This breaks the pattern of how it is everywhere else, which is fine. But I want anyone reading the code to know why the pattern is broken here (llvm-config).

[mgorny]

Add a comment.

[mgorny]

In D131878#3722955, @Ericson2314 wrote:

Can we add comment saying why it is this way? This breaks the pattern of how it is everywhere else, which is fine. But I want anyone reading the code to know why the pattern is broken here (llvm-config).

Done.

[mgorny]

Thanks!

[Ericson2314]

Thanks!

[Ericson2314]

BTW this should be backported to the LLVM 15 release branch too.

[mgorny]

In D131878#3723336, @Ericson2314 wrote:

BTW this should be backported to the LLVM 15 release branch too.

I'm going to open a bug after giving buildbots some time to test it.

[Ericson2314]

Great; sounds good. Happy to review that one too when the time comes.

llvm/CMakeLists.txt

 
 if (CMAKE_BUILD_TYPE AND
     NOT uppercase_CMAKE_BUILD_TYPE MATCHES "^(DEBUG|RELEASE|RELWITHDEBINFO|MINSIZEREL)$")
   message(FATAL_ERROR "Invalid value for CMAKE_BUILD_TYPE: ${CMAKE_BUILD_TYPE}")
 endif()
 
 set(LLVM_LIBDIR_SUFFIX "" CACHE STRING "Define suffix of library directory name (32/64)" )
 
+# LLVM_INSTALL_PACKAGE_DIR needs to be declared prior to adding the tools
+# subdirectory in order to have the value available for llvm-config.
+include(GNUInstallPackageDir)
+set(LLVM_INSTALL_PACKAGE_DIR "${CMAKE_INSTALL_PACKAGEDIR}/llvm" CACHE STRING
+  "Path for CMake subdirectory for LLVM (defaults to '${CMAKE_INSTALL_PACKAGEDIR}/llvm')")
+
 set(LLVM_TOOLS_INSTALL_DIR "${CMAKE_INSTALL_BINDIR}" CACHE STRING
     "Path for binary subdirectory (defaults to '${CMAKE_INSTALL_BINDIR}')")
 mark_as_advanced(LLVM_TOOLS_INSTALL_DIR)
 
 set(LLVM_UTILS_INSTALL_DIR "${LLVM_TOOLS_INSTALL_DIR}" CACHE STRING
     "Path to install LLVM utilities (enabled by LLVM_INSTALL_UTILS=ON) (defaults to LLVM_TOOLS_INSTALL_DIR)")
 mark_as_advanced(LLVM_UTILS_INSTALL_DIR)
 

llvm/cmake/modules/CMakeLists.txt

-include(GNUInstallPackageDir)
 include(ExtendPath)
 include(LLVMDistributionSupport)
 include(FindPrefixFromConfig)
 
-set(LLVM_INSTALL_PACKAGE_DIR "${CMAKE_INSTALL_PACKAGEDIR}/llvm" CACHE STRING
-  "Path for CMake subdirectory for LLVM (defaults to '${CMAKE_INSTALL_PACKAGEDIR}/llvm')")
 # CMAKE_INSTALL_PACKAGEDIR might be absolute, so don't reuse below.
 set(llvm_cmake_builddir "${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/llvm")
 
 # First for users who use an installed LLVM, create the LLVMExports.cmake file.
 set(LLVM_EXPORTS_FILE ${llvm_cmake_builddir}/LLVMExports.cmake)
 get_property(LLVM_EXPORTS GLOBAL PROPERTY LLVM_EXPORTS)
 export(TARGETS ${LLVM_EXPORTS} FILE ${LLVM_EXPORTS_FILE})