[CMake] Factor out config prefix finding logic

[Ericson2314]

Summary

See the docs in the new function for details.

I think I found every instance of this copy pasted code. Polly could
also use it, but currently does something different, so I will save the
behavior change for a future revision.

We get the shared, non-installed CMake modules following the pattern
established in D116472.

It might be good to have LLD and Flang also use this, but that would be
a functional change and so I leave it as future work.

[Ericson2314]

Fix arg order error in Clang

[Ericson2314]

Oh, Flang and LLD are the same. Just do them now then

[Ericson2314]

Get MLIR too

[Ericson2314]

Oops, forgot some includes

[lebedev.ri]

Seems like a cleanup to me, and consistent with D116524.
Soft-accept, but only if D116524 is accepted first.

[beanz]

LGTM

[sebastian-ne]

llvm/CMakeLists.txt

205

Hi, adding this module path overwrites the llvm_check_linker_flag from llvm/cmake/modules/LLVMCheckLinkerFlag.cmake with the one defined in cmake/Modules/CheckLinkerFlag.cmake, which does not check the linker but the compiler.
This breaks our gcc+ld build because ld does not support --color-diagnostics.

Our downstream issue is here: https://github.com/GPUOpen-Drivers/llpc/issues/1645

[Ericson2314]

llvm/CMakeLists.txt

205

Thanks for letting me know. Let's just rename the /cmake one then; nothing there is installed, on purpose, so we can change it freely without worrying breaking an interface used downstream.

I will make a patch for that in the next 2 days if no one beats me to it.

[Ericson2314]

llvm/CMakeLists.txt

205

D117537 fixes this.

clang/CMakeLists.txt

if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
   endif()
 
   set( CLANG_BUILT_STANDALONE 1 )
   set(BACKEND_PACKAGE_STRING "LLVM ${LLVM_PACKAGE_VERSION}")
 else()
   set(BACKEND_PACKAGE_STRING "${PACKAGE_STRING}")
 endif()
 
+if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
+  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
+endif()
+
 # Make sure that our source directory is on the current cmake module path so that
 # we can include cmake files from this directory.
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
+list(INSERT CMAKE_MODULE_PATH 0
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
+  "${LLVM_COMMON_CMAKE_UTILS}/Modules"
+  )
 
 if(LLVM_ENABLE_LIBXML2)
   # Don't look for libxml if we're using MSan, since uninstrumented third party
   # code may call MSan interceptors like strlen, leading to false positives.
   if(NOT LLVM_USE_SANITIZER MATCHES "Memory.*")
     set (LIBXML2_FOUND 0)
     find_package(LibXml2 2.5.3 QUIET)
     if (LIBXML2_FOUND)

clang/cmake/modules/CMakeLists.txt

 include(LLVMDistributionSupport)
+include(FindPrefixFromConfig)
 
 # Generate a list of CMake library targets so that other CMake projects can
 # link against them. LLVM calls its version of this file LLVMExports.cmake, but
 # the usual CMake convention seems to be ${Project}Targets.cmake.
 set(CLANG_INSTALL_PACKAGE_DIR lib${LLVM_LIBDIR_SUFFIX}/cmake/clang)
 set(clang_cmake_builddir "${CMAKE_BINARY_DIR}/${CLANG_INSTALL_PACKAGE_DIR}")
 
 # Keep this in sync with llvm/cmake/CMakeLists.txt!

 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/ClangConfig.cmake.in
   ${clang_cmake_builddir}/ClangConfig.cmake
   @ONLY)
 set(CLANG_CONFIG_CMAKE_DIR)
 set(CLANG_CONFIG_LLVM_CMAKE_DIR)
 
 # Generate ClangConfig.cmake for the install tree.
-set(CLANG_CONFIG_CODE "
-# Compute the installation prefix from this LLVMConfig.cmake file location.
-get_filename_component(CLANG_INSTALL_PREFIX \"\${CMAKE_CURRENT_LIST_FILE}\" PATH)")
-# Construct the proper number of get_filename_component(... PATH)
-# calls to compute the installation prefix.
-string(REGEX REPLACE "/" ";" _count "${CLANG_INSTALL_PACKAGE_DIR}")
-foreach(p ${_count})
-  set(CLANG_CONFIG_CODE "${CLANG_CONFIG_CODE}
-get_filename_component(CLANG_INSTALL_PREFIX \"\${CLANG_INSTALL_PREFIX}\" PATH)")
-endforeach(p)
+find_prefix_from_config(CLANG_CONFIG_CODE CLANG_INSTALL_PREFIX "${CLANG_INSTALL_PACKAGE_DIR}")
 set(CLANG_CONFIG_CMAKE_DIR "\${CLANG_INSTALL_PREFIX}/${CLANG_INSTALL_PACKAGE_DIR}")
 set(CLANG_CONFIG_LLVM_CMAKE_DIR "\${CLANG_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 get_config_exports_includes(Clang CLANG_CONFIG_INCLUDE_EXPORTS)
 set(CLANG_CONFIG_INCLUDE_DIRS
   "\${CLANG_INSTALL_PREFIX}/include"
   )
 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/ClangConfig.cmake.in

cmake/Modules/FindPrefixFromConfig.cmake

+# Find the prefix from the `*Config.cmake` file being generated.
+#
+# When generating an installed `*Config.cmake` file, we often want to be able
+# to refer to the ancestor directory which contains all the installed files.
+#
+# We want to do this without baking in an absolute path when the config file is
+# generated, in order to allow for a "relocatable" binary distribution that
+# doesn't need to know what path it ends up being installed at when it is
+# built.
+#
+# The solution that we know the relative path that the config file will be at
+# within that prefix, like `"${prefix_var}/lib/cmake/${project}"`, so we count
+# the number of components in that path to figure out how many parent dirs we
+# need to traverse from the location of the config file to get to the prefix
+# dir.
+#
+# out_var:
+#   variable to set the "return value" of the function, which is the code to
+#   include in the config file under construction.
+#
+# prefix_var:
+#   Name of the variable to define in the returned code (not directory for the
+#   faller!) that will contain the prefix path.
+#
+# path_to_leave:
+#   Path from the prefix to the config file, a relative path which we wish to
+#   go up and out from to find the prefix directory.
+function(find_prefix_from_config out_var prefix_var path_to_leave)
+  set(config_code
+    "# Compute the installation prefix from this LLVMConfig.cmake file location."
+    "get_filename_component(${prefix_var} \"\${CMAKE_CURRENT_LIST_FILE}\" PATH)")
+  # Construct the proper number of get_filename_component(... PATH)
+  # calls to compute the installation prefix.
+  string(REGEX REPLACE "/" ";" _count "${path_to_leave}")
+  foreach(p ${_count})
+    list(APPEND config_code
+      "get_filename_component(${prefix_var} \"\${${prefix_var}}\" PATH)")
+  endforeach(p)
+  string(REPLACE ";" "\n" config_code "${config_code}")
+  set("${out_var}" "${config_code}" PARENT_SCOPE)
+endfunction()

llvm/CMakeLists.txt

 endif()
 
 option(LLVM_ENABLE_DAGISEL_COV "Debug: Prints tablegen patterns that were used for selecting" OFF)
 option(LLVM_ENABLE_GISEL_COV "Enable collection of GlobalISel rule coverage" OFF)
 if(LLVM_ENABLE_GISEL_COV)
   set(LLVM_GISEL_COV_PREFIX "${CMAKE_BINARY_DIR}/gisel-coverage-" CACHE STRING "Provide a filename prefix to collect the GlobalISel rule coverage")
 endif()
 
+set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
+
 # Add path for custom modules
-set(CMAKE_MODULE_PATH
-  ${CMAKE_MODULE_PATH}
+list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
+  "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   )
 
 # Generate a CompilationDatabase (compile_commands.json file) for our build,
 # for use by clang_complete, YouCompleteMe, etc.
 set(CMAKE_EXPORT_COMPILE_COMMANDS 1)
 
 option(LLVM_INSTALL_BINUTILS_SYMLINKS
   "Install symlinks from the binutils tool names to the corresponding LLVM tools." OFF)

 # Each of them corresponds to llvm-config's.
 set(LLVM_TOOLS_BINARY_DIR ${LLVM_RUNTIME_OUTPUT_INTDIR}) # --bindir
 set(LLVM_LIBRARY_DIR      ${LLVM_LIBRARY_OUTPUT_INTDIR}) # --libdir
 set(LLVM_MAIN_SRC_DIR     ${CMAKE_CURRENT_SOURCE_DIR}  ) # --src-root
 set(LLVM_MAIN_INCLUDE_DIR ${LLVM_MAIN_SRC_DIR}/include ) # --includedir
 set(LLVM_BINARY_DIR       ${CMAKE_CURRENT_BINARY_DIR}  ) # --prefix
 
 set(LLVM_THIRD_PARTY_DIR  ${CMAKE_CURRENT_SOURCE_DIR}/../third-party)
-set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 
 # Note: LLVM_CMAKE_DIR does not include generated files
 set(LLVM_CMAKE_DIR ${LLVM_MAIN_SRC_DIR}/cmake/modules)
 set(LLVM_EXAMPLES_BINARY_DIR ${LLVM_BINARY_DIR}/examples)
 set(LLVM_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
 
 # List of all targets to be built by default:
 set(LLVM_ALL_TARGETS

llvm/cmake/modules/CMakeLists.txt

 include(LLVMDistributionSupport)
+include(FindPrefixFromConfig)
 
 set(LLVM_INSTALL_PACKAGE_DIR lib${LLVM_LIBDIR_SUFFIX}/cmake/llvm)
 set(llvm_cmake_builddir "${LLVM_BINARY_DIR}/${LLVM_INSTALL_PACKAGE_DIR}")
 
 # 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})

 # This should be removed in the future.
 file(COPY .
   DESTINATION ${llvm_cmake_builddir}
   FILES_MATCHING PATTERN *.cmake
   PATTERN CMakeFiles EXCLUDE
   )
 
 # Generate LLVMConfig.cmake for the install tree.
-set(LLVM_CONFIG_CODE "
-# Compute the installation prefix from this LLVMConfig.cmake file location.
-get_filename_component(LLVM_INSTALL_PREFIX \"\${CMAKE_CURRENT_LIST_FILE}\" PATH)")
-# Construct the proper number of get_filename_component(... PATH)
-# calls to compute the installation prefix.
-string(REGEX REPLACE "/" ";" _count "${LLVM_INSTALL_PACKAGE_DIR}")
-foreach(p ${_count})
-  set(LLVM_CONFIG_CODE "${LLVM_CONFIG_CODE}
-get_filename_component(LLVM_INSTALL_PREFIX \"\${LLVM_INSTALL_PREFIX}\" PATH)")
-endforeach(p)
+find_prefix_from_config(LLVM_CONFIG_CODE LLVM_INSTALL_PREFIX "${LLVM_INSTALL_PACKAGE_DIR}")
 set(LLVM_CONFIG_INCLUDE_DIRS "\${LLVM_INSTALL_PREFIX}/include")
 set(LLVM_CONFIG_INCLUDE_DIR "${LLVM_CONFIG_INCLUDE_DIRS}")
 set(LLVM_CONFIG_MAIN_INCLUDE_DIR "${LLVM_CONFIG_INCLUDE_DIRS}")
 set(LLVM_CONFIG_LIBRARY_DIRS "\${LLVM_INSTALL_PREFIX}/lib\${LLVM_LIBDIR_SUFFIX}")
 set(LLVM_CONFIG_CMAKE_DIR "\${LLVM_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 set(LLVM_CONFIG_BINARY_DIR "\${LLVM_INSTALL_PREFIX}")
 set(LLVM_CONFIG_TOOLS_BINARY_DIR "\${LLVM_INSTALL_PREFIX}/bin")