[CMake] Factor out config prefix finding logic

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.

Reviewed By: beanz, lebedev.ri

Differential Revision: https://reviews.llvm.org/D116521

clang/CMakeLists.txt

@@ -192,9 +192,16 @@ else()
   set(BACKEND_PACKAGE_STRING "${PACKAGE_STRING}")
 endif() # standalone
 
+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

clang/cmake/modules/CMakeLists.txt

@@ -1,4 +1,5 @@
 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
@@ -29,16 +30,7 @@ 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)

cmake/Modules/FindPrefixFromConfig.cmake

@@ -0,0 +1,41 @@
+# 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()

flang/cmake/modules/CMakeLists.txt

@@ -1,4 +1,5 @@
 include(ExtendPath)
+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
@@ -29,16 +30,7 @@ set(FLANG_CONFIG_CMAKE_DIR)
 set(FLANG_CONFIG_LLVM_CMAKE_DIR)
 
 # Generate FlangConfig.cmake for the install tree.
-set(FLANG_CONFIG_CODE "
-  # Compute the installation prefix from this LLVMConfig.cmake file location.
-  get_filename_component(FLANG_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 "${FLANG_INSTALL_PACKAGE_DIR}")
-foreach(p ${_count})
-  set(FLANG_CONFIG_CODE "${FLANG_CONFIG_CODE}
-      get_filename_component(FLANG_INSTALL_PREFIX \"\${FLANG_INSTALL_PREFIX}\" PATH)")
-endforeach(p)
+find_prefix_from_config(FLANG_CONFIG_CODE FLANG_INSTALL_PREFIX "${FLANG_INSTALL_PACKAGE_DIR}")
 
 set(FLANG_CONFIG_CMAKE_DIR "\${FLANG_INSTALL_PREFIX}/${FLANG_INSTALL_PACKAGE_DIR}")
 set(FLANG_CONFIG_LLVM_CMAKE_DIR "\${FLANG_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")

lld/cmake/modules/CMakeLists.txt

@@ -1,4 +1,5 @@
 include(ExtendPath)
+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
@@ -29,16 +30,7 @@ set(LLD_CONFIG_CMAKE_DIR)
 set(LLD_CONFIG_LLVM_CMAKE_DIR)
 
 # Generate LLDConfig.cmake for the install tree.
-set(LLD_CONFIG_CODE "
-# Compute the installation prefix from this LLVMConfig.cmake file location.
-get_filename_component(LLD_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 "${LLD_INSTALL_PACKAGE_DIR}")
-foreach(p ${_count})
-  set(LLD_CONFIG_CODE "${LLD_CONFIG_CODE}
-get_filename_component(LLD_INSTALL_PREFIX \"\${LLD_INSTALL_PREFIX}\" PATH)")
-endforeach(p)
+find_prefix_from_config(LLD_CONFIG_CODE LLD_INSTALL_PREFIX "${LLD_INSTALL_PACKAGE_DIR}")
 set(LLD_CONFIG_CMAKE_DIR "\${LLD_INSTALL_PREFIX}/${LLD_INSTALL_PACKAGE_DIR}")
 set(LLD_CONFIG_LLVM_CMAKE_DIR "\${LLD_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 get_config_exports_includes(LLD LLD_CONFIG_INCLUDE_EXPORTS)

llvm/CMakeLists.txt

@@ -200,11 +200,13 @@ 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,
@@ -312,7 +314,6 @@ 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)

llvm/cmake/modules/CMakeLists.txt

@@ -1,4 +1,5 @@
 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}")
@@ -99,16 +100,7 @@ file(COPY .
   )
 
 # 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}")

mlir/CMakeLists.txt

@@ -33,7 +33,16 @@ set(MLIR_BINARY_DIR  ${CMAKE_CURRENT_BINARY_DIR})
 set(MLIR_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
 set(MLIR_TOOLS_DIR   ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
 
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
+if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
+  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
+endif()
+
+# Make sure that our source directory is on the current cmake module path so
+# that we can include cmake files from this directory.
+list(INSERT CMAKE_MODULE_PATH 0
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
+  "${LLVM_COMMON_CMAKE_UTILS}/Modules"
+  )
 
 include(AddMLIR)
 

mlir/cmake/modules/CMakeLists.txt

@@ -1,4 +1,5 @@
 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
@@ -44,16 +45,7 @@ file(COPY .
   )
 
 # Generate MLIRConfig.cmake for the install tree.
-set(MLIR_CONFIG_CODE "
-# Compute the installation prefix from this MLIRConfig.cmake file location.
-get_filename_component(MLIR_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 "${MLIR_INSTALL_PACKAGE_DIR}")
-foreach(p ${_count})
-  set(MLIR_CONFIG_CODE "${MLIR_CONFIG_CODE}
-get_filename_component(MLIR_INSTALL_PREFIX \"\${MLIR_INSTALL_PREFIX}\" PATH)")
-endforeach(p)
+find_prefix_from_config(MLIR_CONFIG_CODE MLIR_INSTALL_PREFIX "${MLIR_INSTALL_PACKAGE_DIR}")
 set(MLIR_CONFIG_CMAKE_DIR "\${MLIR_INSTALL_PREFIX}/${MLIR_INSTALL_PACKAGE_DIR}")
 set(MLIR_CONFIG_LLVM_CMAKE_DIR "\${MLIR_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 get_config_exports_includes(MLIR MLIR_CONFIG_INCLUDE_EXPORTS)