Prepare Compiler-RT for GnuInstallDirs, matching libcxx, document all

This is a second attempt at D101497, which landed as
9a9bc76c0e but had to be reverted in
8cf7ddbdd4.

This issue was that in the case that `COMPILER_RT_INSTALL_PATH` is
empty, expressions like "${COMPILER_RT_INSTALL_PATH}/bin" evaluated to
"/bin" not "bin" as intended and as was originally.

One solution is to make `COMPILER_RT_INSTALL_PATH` always non-empty,
defaulting it to `CMAKE_INSTALL_PREFIX`. D99636 adopted that approach.
But, I think it is more ergonomic to allow those project-specific paths
to be relative the global ones. Also, making install paths absolute by
default inhibits the proper behavior of functions like
`GNUInstallDirs_get_absolute_install_dir` which make relative install
paths absolute in a more complicated way.

Given all this, I will define a function like the one asked for in
https://gitlab.kitware.com/cmake/cmake/-/issues/19568 (and needed for a
similar use-case).

---

Original message:

Instead of using `COMPILER_RT_INSTALL_PATH` through the CMake for
complier-rt, just use it to define variables for the subdirs which
themselves are used.

This preserves compatibility, but later on we might consider getting rid
of `COMPILER_RT_INSTALL_PATH` and just changing the defaults for the
subdir variables directly.

---

There was a seaming bug where the (non-Apple) per-target libdir was
`${target}` not `lib/${target}`. I suspect that has to do with the docs
on `COMPILER_RT_INSTALL_PATH` saying was the library dir when that's no
longer true, so I just went ahead and fixed it, allowing me to define
fewer and more sensible variables.

That last part should be the only behavior changes; everything else
should be a pure refactoring.

---

I added some documentation of these variables too. In particular, I
wanted to highlight the gotcha where `-DSomeCachePath=...` without the
`:PATH` will lead CMake to make the path absolute. See [1] for
discussion of the problem, and [2] for the brief official documentation
they added as a result.

[1]: https://cmake.org/pipermail/cmake/2015-March/060204.html

[2]: https://cmake.org/cmake/help/latest/manual/cmake.1.html#options

In 38b2dec37e the problem was somewhat
misidentified and so `:STRING` was used, but `:PATH` is better as it
sets the correct type from the get-go.

---

D99484 is the main thrust of the `GnuInstallDirs` work. Once this lands,
it should be feasible to follow both of these up with a simple patch for
compiler-rt analogous to the one for libcxx.

Reviewed By: phosek, #libc_abi, #libunwind

Differential Revision: https://reviews.llvm.org/D105765

clang/runtime/CMakeLists.txt

@@ -82,7 +82,7 @@ if(LLVM_BUILD_EXTERNAL_COMPILER_RT AND EXISTS ${COMPILER_RT_SRC_ROOT}/)
                -DLLVM_LIT_ARGS=${LLVM_LIT_ARGS}
                -DCOMPILER_RT_OUTPUT_DIR=${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}
                -DCOMPILER_RT_EXEC_OUTPUT_DIR=${LLVM_RUNTIME_OUTPUT_INTDIR}
-               -DCOMPILER_RT_INSTALL_PATH:STRING=lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}
+               -DCOMPILER_RT_INSTALL_PATH:PATH=lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}
                -DCOMPILER_RT_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
                -DLLVM_LIBDIR_SUFFIX=${LLVM_LIBDIR_SUFFIX}

compiler-rt/cmake/Modules/AddCompilerRT.cmake

@@ -371,7 +371,7 @@ function(add_compiler_rt_runtime name type)
         add_custom_command(TARGET ${libname}
           POST_BUILD  
           COMMAND codesign --sign - $<TARGET_FILE:${libname}>
-          WORKING_DIRECTORY ${COMPILER_RT_LIBRARY_OUTPUT_DIR}
+          WORKING_DIRECTORY ${COMPILER_RT_OUTPUT_LIBRARY_DIR}
         )
       endif()
     endif()
@@ -511,7 +511,7 @@ macro(add_compiler_rt_resource_file target_name file_name component)
   add_custom_target(${target_name} DEPENDS ${dst_file})
   # Install in Clang resource directory.
   install(FILES ${file_name}
-    DESTINATION ${COMPILER_RT_INSTALL_PATH}/share
+    DESTINATION ${COMPILER_RT_INSTALL_DATA_DIR}
     COMPONENT ${component})
   add_dependencies(${component} ${target_name})
 
@@ -528,7 +528,7 @@ macro(add_compiler_rt_script name)
   add_custom_target(${name} DEPENDS ${dst})
   install(FILES ${dst}
     PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE
-    DESTINATION ${COMPILER_RT_INSTALL_PATH}/bin)
+    DESTINATION ${COMPILER_RT_INSTALL_BINARY_DIR})
 endmacro(add_compiler_rt_script src name)
 
 # Builds custom version of libc++ and installs it in <prefix>.

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

@@ -457,8 +457,8 @@ macro(darwin_add_builtin_libraries)
                       PARENT_TARGET builtins
                       LIPO_FLAGS ${${os}_cc_kext_lipo_flags}
                       DEPENDS ${${os}_cc_kext_libs}
-                      OUTPUT_DIR ${COMPILER_RT_LIBRARY_OUTPUT_DIR}
+                      OUTPUT_DIR ${COMPILER_RT_OUTPUT_LIBRARY_DIR}
-                      INSTALL_DIR ${COMPILER_RT_LIBRARY_INSTALL_DIR})
+                      INSTALL_DIR ${COMPILER_RT_INSTALL_LIBRARY_DIR})
     endif()
   endforeach()
 
@@ -467,8 +467,8 @@ macro(darwin_add_builtin_libraries)
                      PARENT_TARGET builtins
                      LIPO_FLAGS ${${os}_builtins_lipo_flags}
                      DEPENDS ${${os}_builtins_libs}
-                     OUTPUT_DIR ${COMPILER_RT_LIBRARY_OUTPUT_DIR}
+                     OUTPUT_DIR ${COMPILER_RT_OUTPUT_LIBRARY_DIR}
-                     INSTALL_DIR ${COMPILER_RT_LIBRARY_INSTALL_DIR})
+                     INSTALL_DIR ${COMPILER_RT_INSTALL_LIBRARY_DIR})
   endforeach()
   darwin_add_embedded_builtin_libraries()
 endmacro()
@@ -506,9 +506,9 @@ macro(darwin_add_embedded_builtin_libraries)
     set(DARWIN_macho_embedded_ARCHS armv6m armv7m armv7em armv7 i386 x86_64)
 
     set(DARWIN_macho_embedded_LIBRARY_OUTPUT_DIR
-      ${COMPILER_RT_OUTPUT_DIR}/lib/macho_embedded)
+      ${COMPILER_RT_OUTPUT_LIBRARY_DIR}/macho_embedded)
     set(DARWIN_macho_embedded_LIBRARY_INSTALL_DIR
-      ${COMPILER_RT_INSTALL_PATH}/lib/macho_embedded)
+      ${COMPILER_RT_INSTALL_LIBRARY_DIR}/macho_embedded)
       
     set(CFLAGS_armv7 "-target thumbv7-apple-darwin-eabi")
     set(CFLAGS_i386 "-march=pentium")

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

@@ -498,18 +498,18 @@ endfunction()
 function(get_compiler_rt_install_dir arch install_dir)
   if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
     get_compiler_rt_target(${arch} target)
-    set(${install_dir} ${COMPILER_RT_INSTALL_PATH}/lib/${target} PARENT_SCOPE)
+    set(${install_dir} ${COMPILER_RT_INSTALL_LIBRARY_DIR}/${target} PARENT_SCOPE)
   else()
-    set(${install_dir} ${COMPILER_RT_LIBRARY_INSTALL_DIR} PARENT_SCOPE)
+    set(${install_dir} ${COMPILER_RT_INSTALL_LIBRARY_DIR} PARENT_SCOPE)
   endif()
 endfunction()
 
 function(get_compiler_rt_output_dir arch output_dir)
   if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
     get_compiler_rt_target(${arch} target)
-    set(${output_dir} ${COMPILER_RT_OUTPUT_DIR}/lib/${target} PARENT_SCOPE)
+    set(${output_dir} ${COMPILER_RT_OUTPUT_LIBRARY_DIR}/${target} PARENT_SCOPE)
   else()
-    set(${output_dir} ${COMPILER_RT_LIBRARY_OUTPUT_DIR} PARENT_SCOPE)
+    set(${output_dir} ${COMPILER_RT_OUTPUT_LIBRARY_DIR} PARENT_SCOPE)
   endif()
 endfunction()
 

compiler-rt/cmake/base-config-ix.cmake

@@ -68,8 +68,8 @@ else()
     "Path where built compiler-rt libraries should be stored.")
   set(COMPILER_RT_EXEC_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/bin CACHE PATH
     "Path where built compiler-rt executables should be stored.")
-  set(COMPILER_RT_INSTALL_PATH ${CMAKE_INSTALL_PREFIX} CACHE PATH
+  set(COMPILER_RT_INSTALL_PATH "" CACHE PATH
-    "Path where built compiler-rt libraries should be installed.")
+    "Prefix for directories where built compiler-rt artifacts should be installed.")
   option(COMPILER_RT_INCLUDE_TESTS "Generate and build compiler-rt unit tests." OFF)
   option(COMPILER_RT_ENABLE_WERROR "Fail and stop if warning is triggered" OFF)
   # Use a host compiler to compile/link tests.
@@ -85,20 +85,45 @@ else()
   set(COMPILER_RT_TEST_COMPILER_ID GNU)
 endif()
 
+function(extend_install_path joined_path current_segment)
+  if("${current_segment}" STREQUAL "")
+    set(temp_path "${COMPILER_RT_INSTALL_PATH}")
+  elseif("${COMPILER_RT_INSTALL_PATH}" STREQUAL "")
+    set(temp_path "${current_segment}")
+  elseif(IS_ABSOLUTE "${current_segment}")
+    message(WARNING "Since \"${current_segment}\" is absolute, it overrides COMPILER_RT_INSTALL_PATH: \"${COMPILER_RT_INSTALL_PATH}\".")
+    set(temp_path "${current_segment}")
+  else()
+    set(temp_path "${COMPILER_RT_INSTALL_PATH}/${current_segment}")
+  endif()
+  set(${joined_path} "${temp_path}" PARENT_SCOPE)
+endfunction()
+
 if(NOT DEFINED COMPILER_RT_OS_DIR)
   string(TOLOWER ${CMAKE_SYSTEM_NAME} COMPILER_RT_OS_DIR)
 endif()
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
-  set(COMPILER_RT_LIBRARY_OUTPUT_DIR
+  set(COMPILER_RT_OUTPUT_LIBRARY_DIR
-    ${COMPILER_RT_OUTPUT_DIR})
+    ${COMPILER_RT_OUTPUT_DIR}/lib)
-  set(COMPILER_RT_LIBRARY_INSTALL_DIR
+  extend_install_path(default_install_path lib)
-    ${COMPILER_RT_INSTALL_PATH})
+  set(COMPILER_RT_INSTALL_LIBRARY_DIR "${default_install_path}" CACHE PATH
-else(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR)
+    "Path where built compiler-rt libraries should be installed.")
-  set(COMPILER_RT_LIBRARY_OUTPUT_DIR
+else(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
+  set(COMPILER_RT_OUTPUT_LIBRARY_DIR
     ${COMPILER_RT_OUTPUT_DIR}/lib/${COMPILER_RT_OS_DIR})
-  set(COMPILER_RT_LIBRARY_INSTALL_DIR
+  extend_install_path(default_install_path "lib/${COMPILER_RT_OS_DIR}")
-    ${COMPILER_RT_INSTALL_PATH}/lib/${COMPILER_RT_OS_DIR})
+  set(COMPILER_RT_INSTALL_LIBRARY_DIR "${default_install_path}" CACHE PATH
+    "Path where built compiler-rt libraries should be installed.")
 endif()
+extend_install_path(default_install_path bin)
+set(COMPILER_RT_INSTALL_BINARY_DIR "${default_install_path}" CACHE PATH
+  "Path where built compiler-rt executables should be installed.")
+extend_install_path(default_install_path include)
+set(COMPILER_RT_INSTALL_INCLUDE_DIR "${default_install_path}" CACHE PATH
+  "Path where compiler-rt headers should be installed.")
+extend_install_path(default_install_path share)
+set(COMPILER_RT_INSTALL_DATA_DIR "${default_install_path}" CACHE PATH
+  "Path where compiler-rt data files should be installed.")
 
 if(APPLE)
   # On Darwin if /usr/include/c++ doesn't exist, the user probably has Xcode but

compiler-rt/docs/BuildingCompilerRT.rst

@@ -0,0 +1,92 @@
+.. _BuildingCompilerRT:
+
+===============
+Building Compiler-RT
+===============
+
+.. contents::
+  :local:
+
+.. _build instructions:
+
+The instructions on this page are aimed at vendors who ship Compiler-RT as part of an
+operating system distribution, a toolchain or similar shipping vehicules. If you
+are a user merely trying to use Compiler-RT in your program, you most likely want to
+refer to your vendor's documentation, or to the general documentation for using
+LLVM, Clang, the various santizers, etc.
+
+CMake Options
+=============
+
+Here are some of the CMake variables that are used often, along with a
+brief explanation and LLVM-specific notes. For full documentation, check the
+CMake docs or execute ``cmake --help-variable VARIABLE_NAME``.
+
+**CMAKE_BUILD_TYPE**:STRING
+  Sets the build type for ``make`` based generators. Possible values are
+  Release, Debug, RelWithDebInfo and MinSizeRel. On systems like Visual Studio
+  the user sets the build type with the IDE settings.
+
+**CMAKE_INSTALL_PREFIX**:PATH
+  Path where LLVM will be installed if "make install" is invoked or the
+  "INSTALL" target is built.
+
+**CMAKE_CXX_COMPILER**:STRING
+  The C++ compiler to use when building and testing Compiler-RT.
+
+
+.. _compiler-rt-specific options:
+
+Compiler-RT specific options
+-----------------------
+
+.. option:: COMPILER_RT_INSTALL_PATH:PATH
+
+  **Default**: ```` (empty relative path)
+
+  Prefix for directories where built Compiler-RT artifacts should be installed.
+  Can be an absolute path, like the default empty string, in which case it is
+  relative ``CMAKE_INSTALL_PREFIX``. If setting a relative path, make sure to
+  include the ``:PATH`` with your ``-D``, i.e. use
+  ``-DCOMPILER_RT_INSTALL_PATH:PATH=...`` not
+  ``-DCOMPILER_RT_INSTALL_PATH=...``, otherwise CMake will convert the
+  path to an absolute path.
+
+.. option:: COMPILER_RT_INSTALL_LIBRARY_DIR:PATH
+
+  **Default**: ``lib``
+
+  Path where built Compiler-RT libraries should be installed. If a relative
+  path, relative to ``COMPILER_RT_INSTALL_PATH``.
+
+.. option:: COMPILER_RT_INSTALL_BINARY_DIR:PATH
+
+  **Default**: ``bin``
+
+  Path where built Compiler-RT executables should be installed. If a relative
+  path, relative to ``COMPILER_RT_INSTALL_PATH``.
+
+.. option:: COMPILER_RT_INSTALL_INCLUDE_DIR:PATH
+
+  **Default**: ``include``
+
+  Path where Compiler-RT headers should be installed. If a relative
+  path, relative to ``COMPILER_RT_INSTALL_PATH``.
+
+.. option:: COMPILER_RT_INSTALL_DATA_DIR:PATH
+
+  **Default**: ``share``
+
+  Path where Compiler-RT data should be installed. If a relative
+  path, relative to ``COMPILER_RT_INSTALL_PATH``.
+
+.. _LLVM-specific variables:
+
+LLVM-specific options
+---------------------
+
+.. option:: LLVM_LIBDIR_SUFFIX:STRING
+
+  Extra suffix to append to the directory where libraries are to be
+  installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
+  to install libraries to ``/usr/lib64``.

compiler-rt/include/CMakeLists.txt

@@ -69,22 +69,22 @@ set_target_properties(compiler-rt-headers PROPERTIES FOLDER "Compiler-RT Misc")
 install(FILES ${SANITIZER_HEADERS}
   COMPONENT compiler-rt-headers
   PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-  DESTINATION ${COMPILER_RT_INSTALL_PATH}/include/sanitizer)
+  DESTINATION ${COMPILER_RT_INSTALL_INCLUDE_DIR}/sanitizer)
 # Install fuzzer headers.
 install(FILES ${FUZZER_HEADERS}
   COMPONENT compiler-rt-headers
   PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-  DESTINATION ${COMPILER_RT_INSTALL_PATH}/include/fuzzer)
+  DESTINATION ${COMPILER_RT_INSTALL_INCLUDE_DIR}/fuzzer)
 # Install xray headers.
 install(FILES ${XRAY_HEADERS}
   COMPONENT compiler-rt-headers
   PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-  DESTINATION ${COMPILER_RT_INSTALL_PATH}/include/xray)
+  DESTINATION ${COMPILER_RT_INSTALL_INCLUDE_DIR}/xray)
 # Install profile headers.
 install(FILES ${PROFILE_HEADERS}
   COMPONENT compiler-rt-headers
   PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-  DESTINATION ${COMPILER_RT_INSTALL_PATH}/include/profile)
+  DESTINATION ${COMPILER_RT_INSTALL_INCLUDE_DIR}/profile)
 
 if (NOT CMAKE_CONFIGURATION_TYPES) # don't add this for IDEs.
   add_custom_target(install-compiler-rt-headers

compiler-rt/lib/dfsan/CMakeLists.txt

@@ -65,4 +65,4 @@ add_custom_command(OUTPUT ${dfsan_abilist_filename}
                    DEPENDS done_abilist.txt libc_ubuntu1404_abilist.txt)
 add_dependencies(dfsan dfsan_abilist)
 install(FILES ${dfsan_abilist_filename}
-        DESTINATION ${COMPILER_RT_INSTALL_PATH}/share)
+        DESTINATION ${COMPILER_RT_INSTALL_DATA_DIR})

libcxx/CMakeLists.txt

@@ -407,9 +407,12 @@ if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE})
   set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
   set(LIBCXX_GENERATED_INCLUDE_TARGET_DIR "${LLVM_BINARY_DIR}/include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1")
-  set(LIBCXX_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE})
+  set(LIBCXX_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE} CACHE PATH
-  set(LIBCXX_INSTALL_INCLUDE_DIR "include/c++/v1")
+      "Path where built libc++ libraries should be installed.")
-  set(LIBCXX_INSTALL_INCLUDE_TARGET_DIR "include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1")
+  set(LIBCXX_INSTALL_INCLUDE_DIR "include/c++/v1" CACHE PATH
+      "Path where target-agnostic libc++ headers should be installed.")
+  set(LIBCXX_INSTALL_INCLUDE_TARGET_DIR "include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1" CACHE PATH
+      "Path where target-specific libc++ headers should be installed.")
   if(LIBCXX_LIBDIR_SUBDIR)
     string(APPEND LIBCXX_LIBRARY_DIR /${LIBCXX_LIBDIR_SUBDIR})
     string(APPEND LIBCXX_INSTALL_LIBRARY_DIR /${LIBCXX_LIBDIR_SUBDIR})
@@ -418,16 +421,22 @@ elseif(LLVM_LIBRARY_OUTPUT_INTDIR)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
   set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
   set(LIBCXX_GENERATED_INCLUDE_TARGET_DIR "${LIBCXX_GENERATED_INCLUDE_DIR}")
-  set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX})
+  set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX} CACHE PATH
-  set(LIBCXX_INSTALL_INCLUDE_DIR "include/c++/v1")
+      "Path where built libc++ libraries should be installed.")
-  set(LIBCXX_INSTALL_INCLUDE_TARGET_DIR "${LIBCXX_INSTALL_INCLUDE_DIR}")
+  set(LIBCXX_INSTALL_INCLUDE_DIR "include/c++/v1" CACHE PATH
+      "Path where target-agnostic libc++ headers should be installed.")
+  set(LIBCXX_INSTALL_INCLUDE_TARGET_DIR "${LIBCXX_INSTALL_INCLUDE_DIR}" CACHE PATH
+      "Path where target-specific libc++ headers should be installed.")
 else()
   set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})
   set(LIBCXX_GENERATED_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include/c++/v1")
   set(LIBCXX_GENERATED_INCLUDE_TARGET_DIR "${LIBCXX_GENERATED_INCLUDE_DIR}")
-  set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX})
+  set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX} CACHE PATH
-  set(LIBCXX_INSTALL_INCLUDE_DIR "include/c++/v1")
+      "Path where built libc++ libraries should be installed.")
-  set(LIBCXX_INSTALL_INCLUDE_TARGET_DIR "${LIBCXX_INSTALL_INCLUDE_DIR}")
+  set(LIBCXX_INSTALL_INCLUDE_DIR "include/c++/v1" CACHE PATH
+      "Path where target-agnostic libc++ headers should be installed.")
+  set(LIBCXX_INSTALL_INCLUDE_TARGET_DIR "${LIBCXX_INSTALL_INCLUDE_DIR}" CACHE PATH
+      "Path where target-specific libc++ headers should be installed.")
 endif()
 
 file(MAKE_DIRECTORY "${LIBCXX_BINARY_INCLUDE_DIR}")

libcxx/docs/BuildingLibcxx.rst

@@ -251,6 +251,28 @@ libc++ specific options
    This option can be used to enable or disable the filesystem components on
    platforms that may not support them. For example on Windows.
 
+.. option:: LIBCXX_INSTALL_LIBRARY_DIR:PATH
+
+  **Default**: ``lib${LIBCXX_LIBDIR_SUFFIX}``
+
+  Path where built libc++ libraries should be installed. If a relative path,
+  relative to ``CMAKE_INSTALL_PREFIX``.
+
+.. option:: LIBCXX_INSTALL_INCLUDE_DIR:PATH
+
+  **Default**: ``include/c++/v1``
+
+  Path where target-agnostic libc++ headers should be installed. If a relative
+  path, relative to ``CMAKE_INSTALL_PREFIX``.
+
+.. option:: LIBCXX_INSTALL_INCLUDE_TARGET_DIR:PATH
+
+  **Default**: ``include/c++/v1`` or
+  ``include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1``
+
+  Path where target-specific libc++ headers should be installed. If a relative
+  path, relative to ``CMAKE_INSTALL_PREFIX``.
+
 .. _libc++experimental options:
 
 libc++experimental Specific Options

libcxxabi/CMakeLists.txt

@@ -195,7 +195,8 @@ set(CMAKE_MODULE_PATH
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   set(LIBCXXABI_HEADER_DIR ${LLVM_BINARY_DIR})
   set(LIBCXXABI_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE})
-  set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE})
+  set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE} CACHE PATH
+      "Path where built libc++abi libraries should be installed.")
   if(LIBCXX_LIBDIR_SUBDIR)
     string(APPEND LIBCXXABI_LIBRARY_DIR /${LIBCXXABI_LIBDIR_SUBDIR})
     string(APPEND LIBCXXABI_INSTALL_LIBRARY_DIR /${LIBCXXABI_LIBDIR_SUBDIR})
@@ -203,11 +204,13 @@ if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
 elseif(LLVM_LIBRARY_OUTPUT_INTDIR)
   set(LIBCXXABI_HEADER_DIR ${LLVM_BINARY_DIR})
   set(LIBCXXABI_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
-  set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LIBCXXABI_LIBDIR_SUFFIX})
+  set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LIBCXXABI_LIBDIR_SUFFIX} CACHE PATH
+      "Path where built libc++abi libraries should be installed.")
 else()
   set(LIBCXXABI_HEADER_DIR ${CMAKE_BINARY_DIR})
   set(LIBCXXABI_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXXABI_LIBDIR_SUFFIX})
-  set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LIBCXXABI_LIBDIR_SUFFIX})
+  set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LIBCXXABI_LIBDIR_SUFFIX} CACHE PATH
+      "Path where built libc++abi libraries should be installed.")
 endif()
 
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBCXXABI_LIBRARY_DIR})

libunwind/CMakeLists.txt

@@ -116,17 +116,20 @@ set(CMAKE_MODULE_PATH
 
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   set(LIBUNWIND_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE})
-  set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE})
+  set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE} CACHE PATH
+      "Path where built libunwind libraries should be installed.")
   if(LIBCXX_LIBDIR_SUBDIR)
     string(APPEND LIBUNWIND_LIBRARY_DIR /${LIBUNWIND_LIBDIR_SUBDIR})
     string(APPEND LIBUNWIND_INSTALL_LIBRARY_DIR /${LIBUNWIND_LIBDIR_SUBDIR})
   endif()
 elseif(LLVM_LIBRARY_OUTPUT_INTDIR)
   set(LIBUNWIND_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
-  set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LIBUNWIND_LIBDIR_SUFFIX})
+  set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LIBUNWIND_LIBDIR_SUFFIX} CACHE PATH
+      "Path where built libunwind libraries should be installed.")
 else()
   set(LIBUNWIND_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBUNWIND_LIBDIR_SUFFIX})
-  set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LIBUNWIND_LIBDIR_SUFFIX})
+  set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LIBUNWIND_LIBDIR_SUFFIX} CACHE PATH
+      "Path where built libunwind libraries should be installed.")
 endif()
 
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBUNWIND_LIBRARY_DIR})

libunwind/docs/BuildingLibunwind.rst

@@ -159,3 +159,10 @@ libunwind specific options
 .. option:: LIBUNWIND_SYSROOT
 
   Sysroot for cross compiling
+
+.. option:: LIBUNWIND_INSTALL_LIBRARY_DIR:PATH
+
+  **Default**: ``lib${LIBUNWIND_LIBDIR_SUFFIX}``
+
+  Path where built libunwind libraries should be installed. If a relative path,
+  relative to ``CMAKE_INSTALL_PREFIX``.