[cmake] Use `GNUInstallDirs` to support custom installation dirs.

This is the original patch in my GNUInstallDirs series, now last to merge as the final piece!

It arose as a new draft of D28234. I initially did the unorthodox thing of pushing to that when I wasn't the original author, but since I ended up

 - Using `GNUInstallDirs`, rather than mimicking it, as the original author was hesitant to do but others requested.

 - Converting all the packages, not just LLVM, effecting many more projects than LLVM itself.

I figured it was time to make a new revision.

I have used this patch series (and many back-ports) as the basis of https://github.com/NixOS/nixpkgs/pull/111487 for my distro (NixOS), which was merged last spring (2021). It looked like people were generally on board in D28234, but I make note of this here in case extra motivation is useful.

---

As pointed out in the original issue, a central tension is that LLVM already has some partial support for these sorts of things. Variables like `COMPILER_RT_INSTALL_PATH` have already been dealt with. Variables like `LLVM_LIBDIR_SUFFIX` however, will require further work, so that we may use `CMAKE_INSTALL_LIBDIR`.

These remaining items will be addressed in further patches. What is here is now rote and so we should get it out of the way before dealing more intricately with the remainder.

Reviewed By: #libunwind, #libc, #libc_abi, compnerd

Differential Revision: https://reviews.llvm.org/D99484

3 files changed, 16 insertions, 12 deletions

diff --git a/polly/CMakeLists.txt b/polly/CMakeLists.txt
index fb62dbd3a09b..d6bcc8f7f285 100644
--- a/polly/CMakeLists.txt
+++ b/polly/CMakeLists.txt
@@ -1,3 +1,5 @@
+include(GNUInstallDirs)
+
 # Check if this is a in tree build.
 if (NOT DEFINED LLVM_MAIN_SRC_DIR)
   project(Polly)
@@ -124,13 +126,13 @@ include_directories(
 
 if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   install(DIRECTORY include/
-    DESTINATION include
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
     FILES_MATCHING
     PATTERN "*.h"
     )
 
   install(DIRECTORY ${POLLY_BINARY_DIR}/include/
-    DESTINATION include
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
     FILES_MATCHING
     PATTERN "*.h"
     PATTERN "CMakeFiles" EXCLUDE
diff --git a/polly/cmake/CMakeLists.txt b/polly/cmake/CMakeLists.txt
index 524d6069c117..9b508941a139 100644
--- a/polly/cmake/CMakeLists.txt
+++ b/polly/cmake/CMakeLists.txt
@@ -1,5 +1,6 @@
 # Keep this in sync with llvm/cmake/CMakeLists.txt!
 
+include(ExtendPath)
 include(FindPrefixFromConfig)
 
 set(LLVM_INSTALL_PACKAGE_DIR "lib${LLVM_LIBDIR_SUFFIX}/cmake/llvm")
@@ -83,17 +84,18 @@ file(GENERATE
 # Generate PollyConfig.cmake for the install tree.
 unset(POLLY_EXPORTS)
 find_prefix_from_config(POLLY_CONFIG_CODE POLLY_INSTALL_PREFIX "${POLLY_INSTALL_PACKAGE_DIR}")
-set(POLLY_CONFIG_LLVM_CMAKE_DIR "\${POLLY_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
-set(POLLY_CONFIG_CMAKE_DIR "\${POLLY_INSTALL_PREFIX}/${POLLY_INSTALL_PACKAGE_DIR}")
-set(POLLY_CONFIG_LIBRARY_DIRS "\${POLLY_INSTALL_PREFIX}/lib${LLVM_LIBDIR_SUFFIX}")
+extend_path(POLLY_CONFIG_LLVM_CMAKE_DIR "\${POLLY_INSTALL_PREFIX}" "${LLVM_INSTALL_PACKAGE_DIR}")
+extend_path(POLLY_CONFIG_CMAKE_DIR "\${POLLY_INSTALL_PREFIX}" "${POLLY_INSTALL_PACKAGE_DIR}")
+extend_path(POLLY_CONFIG_LIBRARY_DIRS "\${POLLY_INSTALL_PREFIX}" "lib${LLVM_LIBDIR_SUFFIX}")
+extend_path(base_includedir "\${POLLY_INSTALL_PREFIX}" "${CMAKE_INSTALL_INCLUDEDIR}")
 if (POLLY_BUNDLED_ISL)
   set(POLLY_CONFIG_INCLUDE_DIRS
-    "\${POLLY_INSTALL_PREFIX}/include"
-    "\${POLLY_INSTALL_PREFIX}/include/polly"
+    "${base_includedir}"
+    "${base_includedir}/polly"
     )
 else()
   set(POLLY_CONFIG_INCLUDE_DIRS
-    "\${POLLY_INSTALL_PREFIX}/include"
+    "${base_includedir}"
     ${ISL_INCLUDE_DIRS}
     )
 endif()
@@ -110,12 +112,12 @@ set(POLLY_EXPORTS
 foreach(tgt IN LISTS POLLY_CONFIG_EXPORTED_TARGETS)
   get_target_property(tgt_type ${tgt} TYPE)
   if (tgt_type STREQUAL "EXECUTABLE")
-    set(tgt_prefix "bin/")
+    set(tgt_prefix "${CMAKE_INSTALL_BINDIR}/")
   else()
-    set(tgt_prefix "lib/")
+    set(tgt_prefix "${CMAKE_INSTALL_LIBDIR}/")
   endif()
 
-  set(tgt_path "\${POLLY_INSTALL_PREFIX}/${tgt_prefix}$<TARGET_FILE_NAME:${tgt}>")
+  extend_path(tgt_path "\${POLLY_INSTALL_PREFIX}" "${tgt_prefix}$<TARGET_FILE_NAME:${tgt}>")
 
   if (NOT tgt_type STREQUAL "INTERFACE_LIBRARY")
     set(POLLY_EXPORTS
diff --git a/polly/lib/External/CMakeLists.txt b/polly/lib/External/CMakeLists.txt
index e3a5683fccdc..2f912e7daeb2 100644
--- a/polly/lib/External/CMakeLists.txt
+++ b/polly/lib/External/CMakeLists.txt
@@ -290,7 +290,7 @@ if (POLLY_BUNDLED_ISL)
     install(DIRECTORY
       ${ISL_SOURCE_DIR}/include/
       ${ISL_BINARY_DIR}/include/
-      DESTINATION include/polly
+      DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/polly"
       FILES_MATCHING
       PATTERN "*.h"
       PATTERN "CMakeFiles" EXCLUDE