Revert "Revert "Revert "[CMake] Bumps minimum version to 3.20.0."""

This reverts commit 1ef4c3c859. Two buildbots still haven't been updated.
2024-11-23 05:40:09 +00:00 · 2023-04-15 20:12:24 +02:00 · 2023-04-15 20:12:24 +02:00 · 44d38022ab
commit 44d38022ab
parent d3df7b1568
37 changed files with 138 additions and 44 deletions
--- a/bolt/runtime/CMakeLists.txt
+++ b/bolt/runtime/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)
 include(CheckIncludeFiles)
 include(GNUInstallDirs)

--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
@ -11,6 +11,13 @@ include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  project(Clang)
  set(CLANG_BUILT_STANDALONE TRUE)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 endif()

 # Must go below project(..)
--- a/clang/tools/scan-build-py/tests/functional/exec/CMakeLists.txt
+++ b/clang/tools/scan-build-py/tests/functional/exec/CMakeLists.txt
@ -1,6 +1,6 @@
 project(exec C)

-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 include(CheckCCompilerFlag)
 check_c_compiler_flag("-std=c99" C99_SUPPORTED)
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@ -3,13 +3,20 @@
 # An important constraint of the build is that it only produces libraries
 # based on the ability of the host toolchain to target various platforms.

-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 # Check if compiler-rt is built as a standalone project.
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR OR COMPILER_RT_STANDALONE_BUILD)
  project(CompilerRT C CXX ASM)
  set(COMPILER_RT_STANDALONE_BUILD TRUE)
  set_property(GLOBAL PROPERTY USE_FOLDERS ON)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 endif()

 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@ -3,7 +3,14 @@
 # architecture-specific code in various subdirectories.

 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()

  set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
  project(CompilerRTBuiltins C ASM)
--- a/compiler-rt/lib/crt/CMakeLists.txt
+++ b/compiler-rt/lib/crt/CMakeLists.txt
@ -1,5 +1,12 @@
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()

  set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
  project(CompilerRTCRT C)
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
@ -31,6 +31,13 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  message("Building Flang as a standalone project.")
  project(Flang)
  set(FLANG_STANDALONE_BUILD ON)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 else()
  set(FLANG_STANDALONE_BUILD OFF)
 endif()
--- a/flang/lib/Decimal/CMakeLists.txt
+++ b/flang/lib/Decimal/CMakeLists.txt
@ -1,5 +1,5 @@
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)

  project(FortranDecimal C CXX)

--- a/flang/runtime/CMakeLists.txt
+++ b/flang/runtime/CMakeLists.txt
@ -7,7 +7,14 @@
 #===------------------------------------------------------------------------===#

 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()

  project(FlangRuntime C CXX)

--- a/libc/CMakeLists.txt
+++ b/libc/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 # Include LLVM's cmake policies.
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
--- a/libc/examples/hello_world/CMakeLists.txt
+++ b/libc/examples/hello_world/CMakeLists.txt
@ -1,5 +1,5 @@
 project(hello_world)
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)
 include(../examples.cmake)

 add_example(
--- a/libclc/CMakeLists.txt
+++ b/libclc/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 project( libclc VERSION 0.2.0 LANGUAGES CXX C)

--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@ -4,7 +4,7 @@
 #===============================================================================
 # Setup Project
 #===============================================================================
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")

--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@ -4,7 +4,7 @@
 # Setup Project
 #===============================================================================

-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")

--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@ -2,7 +2,7 @@
 # Setup Project
 #===============================================================================

-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")

--- a/libunwind/src/CMakeLists.txt
+++ b/libunwind/src/CMakeLists.txt
@ -35,7 +35,8 @@ set(LIBUNWIND_ASM_SOURCES
 # CMake doesn't work correctly with assembly on AIX. Workaround by compiling
 # as C files as well.
 if((APPLE AND CMAKE_VERSION VERSION_LESS 3.19) OR
-   (MINGW AND CMAKE_VERSION VERSION_LESS 3.17))
+   (MINGW AND CMAKE_VERSION VERSION_LESS 3.17) OR
+   (${CMAKE_SYSTEM_NAME} MATCHES "AIX"))
  set_source_files_properties(${LIBUNWIND_ASM_SOURCES} PROPERTIES LANGUAGE C)
 endif()

--- a/lld/CMakeLists.txt
+++ b/lld/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
@ -11,6 +11,13 @@ include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  project(lld)
  set(LLD_BUILT_STANDALONE TRUE)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 endif()

 # Must go below project(..)
--- a/lldb/CMakeLists.txt
+++ b/lldb/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
@ -19,6 +19,13 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  project(lldb)
  set(LLDB_BUILT_STANDALONE TRUE)
  set(LLVM_INCLUDE_TESTS ON CACHE INTERNAL "")
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 endif()

 # Must go below project(..)
--- a/lldb/tools/debugserver/CMakeLists.txt
+++ b/lldb/tools/debugserver/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 project(Debugserver LANGUAGES C CXX ASM-ATT)

@ -7,6 +7,13 @@ include(GNUInstallDirs)

 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  set(LLDB_BUILT_STANDALONE TRUE)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()

  set(CMAKE_MODULE_PATH
    ${CMAKE_MODULE_PATH}
--- a/llvm-libgcc/CMakeLists.txt
+++ b/llvm-libgcc/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 if (NOT IS_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/../libunwind")
  message(FATAL_ERROR "llvm-libgcc requires being built in a monorepo layout with libunwind available")
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@ -1,6 +1,13 @@
 # See docs/CMake.html for instructions about how to build LLVM with CMake.

-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)
+if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+  message(WARNING
+    "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+    "minimum version of CMake required to build LLVM will become 3.20.0, and "
+    "using an older CMake will become an error. Please upgrade your CMake to "
+    "at least 3.20.0 now to avoid issues in the future!")
+endif()

 set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
--- a/llvm/docs/CMake.rst
+++ b/llvm/docs/CMake.rst
@ -34,7 +34,7 @@ Quick start
 We use here the command-line, non-interactive CMake interface.

 #. `Download <http://www.cmake.org/cmake/resources/software.html>`_ and install
-   CMake. Version 3.20.0 is the minimum required.
+   CMake. Version 3.13.4 is the minimum required.

 #. Open a shell. Your development tools must be reachable from this shell
   through the PATH environment variable.
@ -911,7 +911,7 @@ and uses them to build a simple application ``simple-tool``.

 .. code-block:: cmake

-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
  project(SimpleProject)

  find_package(LLVM REQUIRED CONFIG)
--- a/llvm/docs/GettingStarted.rst
+++ b/llvm/docs/GettingStarted.rst
@ -280,7 +280,7 @@ uses the package and provides other details.
 =========================================================== ============ ==========================================
 Package                                                     Version      Notes
 =========================================================== ============ ==========================================
-`CMake <http://cmake.org/>`__                               >=3.20.0     Makefile/workspace generator
+`CMake <http://cmake.org/>`__                               >=3.13.4     Makefile/workspace generator
 `GCC <http://gcc.gnu.org/>`_                                >=7.1.0      C/C++ compiler\ :sup:`1`
 `python <http://www.python.org/>`_                          >=3.6        Automated test suite\ :sup:`2`
 `zlib <http://zlib.net>`_                                   >=1.2.3.4    Compression library\ :sup:`3`
--- a/llvm/docs/ReleaseNotes.rst
+++ b/llvm/docs/ReleaseNotes.rst
@ -47,11 +47,6 @@ Non-comprehensive list of changes in this release
 Update on required toolchains to build LLVM
 -------------------------------------------

-With LLVM 17.x we raised the version requirement of CMake used to build LLVM.
-The new requirements are as follows:
-
-* CMake >= 3.20.0
-
 Changes to the LLVM IR
 ----------------------

--- a/mlir/CMakeLists.txt
+++ b/mlir/CMakeLists.txt
@ -1,5 +1,5 @@
 # MLIR project.
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
  set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
@ -11,6 +11,13 @@ include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  project(mlir)
  set(MLIR_STANDALONE_BUILD TRUE)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 endif()

 # Must go below project(..)
--- a/mlir/examples/standalone/CMakeLists.txt
+++ b/mlir/examples/standalone/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)
 project(standalone-dialect LANGUAGES CXX C)

 set(CMAKE_BUILD_WITH_INSTALL_NAME_DIR ON)
--- a/openmp/CMakeLists.txt
+++ b/openmp/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)

@ -12,6 +12,13 @@ list(INSERT CMAKE_MODULE_PATH 0
 if (OPENMP_STANDALONE_BUILD OR "${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
  set(OPENMP_STANDALONE_BUILD TRUE)
  project(openmp C CXX)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
 endif()

 # Must go below project(..)
--- a/openmp/cmake/DetectTestCompiler/CMakeLists.txt
+++ b/openmp/cmake/DetectTestCompiler/CMakeLists.txt
@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)
 project(DetectTestCompiler C CXX)

 include(CheckCCompilerFlag)
--- a/openmp/docs/SupportAndFAQ.rst
+++ b/openmp/docs/SupportAndFAQ.rst
@ -307,7 +307,7 @@ require a few additions.

 .. code-block:: cmake

-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
  project(offloadTest VERSION 1.0 LANGUAGES CXX)

  list(APPEND CMAKE_MODULE_PATH "${PATH_TO_OPENMP_INSTALL}/lib/cmake/openmp")
@ -318,7 +318,7 @@ require a few additions.
  target_link_libraries(offload PRIVATE OpenMPTarget::OpenMPTarget_NVPTX)
  target_sources(offload PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src/Main.cpp)

-Using this module requires at least CMake version 3.20.0. Supported languages
+Using this module requires at least CMake version 3.13.4. Supported languages
 are C and C++ with Fortran support planned in the future. Compiler support is
 best for Clang but this module should work for other compiler vendors such as
 IBM, GNU.
--- a/openmp/libompd/src/CMakeLists.txt
+++ b/openmp/libompd/src/CMakeLists.txt
@ -9,7 +9,7 @@
 #

 project (libompd)
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 add_library (ompd SHARED TargetValue.cpp omp-debug.cpp omp-state.cpp omp-icv.cpp)

--- a/openmp/libomptarget/plugins/remote/src/CMakeLists.txt
+++ b/openmp/libomptarget/plugins/remote/src/CMakeLists.txt
@ -10,7 +10,7 @@
 #
 ##===----------------------------------------------------------------------===##

-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 # Define the suffix for the runtime messaging dumps.
 add_definitions(-DTARGET_NAME=RPC)
--- a/openmp/runtime/cmake/LibompCheckLinkerFlag.cmake
+++ b/openmp/runtime/cmake/LibompCheckLinkerFlag.cmake
@ -19,7 +19,7 @@ function(libomp_check_linker_flag flag boolean)
  set(library_source
    "int foo(int a) { return a*a; }")
  set(cmake_source
-    "cmake_minimum_required(VERSION 3.20.0)
+    "cmake_minimum_required(VERSION 3.13.4)
     project(foo C)
     set(CMAKE_SHARED_LINKER_FLAGS \"${flag}\")
     add_library(foo SHARED src_to_link.c)")
--- a/openmp/tools/Modules/FindOpenMPTarget.cmake
+++ b/openmp/tools/Modules/FindOpenMPTarget.cmake
@ -79,7 +79,7 @@ be used to override the standard flag searching for a given compiler.
 # TODO: Test more compilers

 cmake_policy(PUSH)
-cmake_policy(VERSION 3.20.0)
+cmake_policy(VERSION 3.13.4)

 find_package(OpenMP ${OpenMPTarget_FIND_VERSION} REQUIRED)

--- a/openmp/tools/Modules/README.rst
+++ b/openmp/tools/Modules/README.rst
@ -26,7 +26,7 @@ require a few additions.

 .. code-block:: cmake

-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
  project(offloadTest VERSION 1.0 LANGUAGES CXX)

  list(APPEND CMAKE_MODULE_PATH "${PATH_TO_OPENMP_INSTALL}/lib/cmake/openmp")
@ -37,7 +37,7 @@ require a few additions.
  target_link_libraries(offload PRIVATE OpenMPTarget::OpenMPTarget_NVPTX)
  target_sources(offload PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src/Main.cpp)

-Using this module requires at least CMake version 3.20.0. Supported languages
+Using this module requires at least CMake version 3.13.4. Supported languages
 are C and C++ with Fortran support planned in the future. If your application
 requires building for a specific device architecture you can set the
 ``OpenMPTarget_<device>_ARCH=<flag>`` variable. Compiler support is best for
--- a/polly/CMakeLists.txt
+++ b/polly/CMakeLists.txt
@ -1,7 +1,14 @@
 # Check if this is a in tree build.
 if (NOT DEFINED LLVM_MAIN_SRC_DIR)
  project(Polly)
-  cmake_minimum_required(VERSION 3.20.0)
+  cmake_minimum_required(VERSION 3.13.4)
+  if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+    message(WARNING
+      "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+      "minimum version of CMake required to build LLVM will become 3.20.0, and "
+      "using an older CMake will become an error. Please upgrade your CMake to "
+      "at least 3.20.0 now to avoid issues in the future!")
+  endif()
  set(POLLY_STANDALONE_BUILD TRUE)
 endif()

--- a/pstl/CMakeLists.txt
+++ b/pstl/CMakeLists.txt
@ -5,7 +5,7 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===----------------------------------------------------------------------===##
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)

 set(PARALLELSTL_VERSION_FILE "${CMAKE_CURRENT_SOURCE_DIR}/include/pstl/internal/pstl_config.h")
 file(STRINGS "${PARALLELSTL_VERSION_FILE}" PARALLELSTL_VERSION_SOURCE REGEX "#define _PSTL_VERSION .*$")
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@ -1,5 +1,12 @@
 # This file handles building LLVM runtime sub-projects.
-cmake_minimum_required(VERSION 3.20.0)
+cmake_minimum_required(VERSION 3.13.4)
+if ("${CMAKE_VERSION}" VERSION_LESS "3.20.0")
+  message(WARNING
+    "Your CMake version is ${CMAKE_VERSION}. Starting with LLVM 17.0.0, the "
+    "minimum version of CMake required to build LLVM will become 3.20.0, and "
+    "using an older CMake will become an error. Please upgrade your CMake to "
+    "at least 3.20.0 now to avoid issues in the future!")
+endif()
 project(Runtimes C CXX ASM)

 # Add path for custom and the LLVM build's modules to the CMake module path.