[CMake] Bumps minimum version to 3.20.0.

[Mordante]

Summary

This partly undoes D137724.

This change has been discussed on discourse
https://discourse.llvm.org/t/rfc-upgrading-llvms-minimum-required-cmake-version/66193

Note this does not remove work-arounds for older CMake versions, that
will be done in followup patches.

[sivachandra]

OK for libc.

[phosek]

LGTM

[Mordante]

Try to fix AIX CI.

[Mordante]

Rebased to test CI.

[glandium]

FYI, 65429b9af6a2c99d340ab2dcddd41dab201f399c is causing problems on Windows compiler-rt for some reason I haven't identified yet (with cmake 3.25.1). Which suggests for a same version of cmake, this is actually altering its behavior, which I wouldn't have expected...

[mstorsjo]

In D144509#4347562, @glandium wrote:

FYI, 65429b9af6a2c99d340ab2dcddd41dab201f399c is causing problems on Windows compiler-rt for some reason I haven't identified yet (with cmake 3.25.1). Which suggests for a same version of cmake, this is actually altering its behavior, which I wouldn't have expected...

See D150688 - I believe that might fix the issue you're seeing, as that one mentions compiler-rt.

[glandium]

In D144509#4347604, @mstorsjo wrote:

See D150688 - I believe that might fix the issue you're seeing, as that one mentions compiler-rt.

Unfortunately, it doesn't.

FWIW, the errors looks like:

lld-link: error: undefined symbol: __declspec(dllimport) _getpid
>>> referenced by clang_rt.profile-i386.lib(InstrProfilingFile.c.obj):(_getCurFilename)
>>> referenced by clang_rt.profile-i386.lib(InstrProfilingFile.c.obj):(_parseAndSetFilename)
>>> referenced by oldnames.lib(getpid.obi)

etc.

[glandium]

It's related, though, because now that I look at my build logs, the difference between when it works and when it doesn't is /MT vs -MD when compiler-rt is compiled. The main peculiarity on our end, though, is that the Windows compiler-rt is cross-compiled.

[glandium]

So the problem is that CMakePolicy.cmake is not included in compiler-rt/CMakeLists.txt.

[dyung]

I'm not really sure where else to post this, but the pre-merge linux bot still seems to be running 3.18.4.

https://buildkite.com/llvm-project/premerge-checks/builds/152678#018828d2-1837-4fc2-baec-fca595969219

CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.20.0 or higher is required.  You are running version 3.18.4

[hans]

In D144509#4347562, @glandium wrote:

FYI, 65429b9af6a2c99d340ab2dcddd41dab201f399c is causing problems on Windows compiler-rt for some reason I haven't identified yet (with cmake 3.25.1). Which suggests for a same version of cmake, this is actually altering its behavior, which I wouldn't have expected...

It is indeed unfortunate that this seems to come with such a fundamental behavior change. (we already have https://github.com/llvm/llvm-project/issues/62719) Do you have a repro for the issue you're seeing?

Since the breakages are piling up, perhaps it's time to revert this.

[mstorsjo]

In D144509#4349051, @hans wrote:

In D144509#4347562, @glandium wrote:

FYI, 65429b9af6a2c99d340ab2dcddd41dab201f399c is causing problems on Windows compiler-rt for some reason I haven't identified yet (with cmake 3.25.1). Which suggests for a same version of cmake, this is actually altering its behavior, which I wouldn't have expected...

It is indeed unfortunate that this seems to come with such a fundamental behavior change. (we already have https://github.com/llvm/llvm-project/issues/62719) Do you have a repro for the issue you're seeing?

Since the breakages are piling up, perhaps it's time to revert this.

Unfortunately, much of this is hard to sort out without actually trying to patch forward on main, since many of these issues don't show up easily in e.g. premerge testing or similar (the patch has been tried many times for months before in that form), so I'd appreciate if we'd give it a little more time to actually try to sort out the issues...

[hans]

In D144509#4349399, @mstorsjo wrote:

In D144509#4349051, @hans wrote:

In D144509#4347562, @glandium wrote:

FYI, 65429b9af6a2c99d340ab2dcddd41dab201f399c is causing problems on Windows compiler-rt for some reason I haven't identified yet (with cmake 3.25.1). Which suggests for a same version of cmake, this is actually altering its behavior, which I wouldn't have expected...

It is indeed unfortunate that this seems to come with such a fundamental behavior change. (we already have https://github.com/llvm/llvm-project/issues/62719) Do you have a repro for the issue you're seeing?

Since the breakages are piling up, perhaps it's time to revert this.

Unfortunately, much of this is hard to sort out without actually trying to patch forward on main, since many of these issues don't show up easily in e.g. premerge testing or similar (the patch has been tried many times for months before in that form), so I'd appreciate if we'd give it a little more time to actually try to sort out the issues...

But now we have identified issues and there are reproducers available (e.g. on https://github.com/llvm/llvm-project/issues/62719). Keeping it in main is just disruptive and risks making reverting harder (it's already not a clean revert). I think the policy of reverting back to green still applies.

[thakis]

Reverted this and follow-ups in d763c6e5e2d0a6b34097aa7dabca31e9aff9b0b6 for now.

Sorry this is such a pain to land :(

(See also discussion over in D150688)

[Mordante]

In D144509#4349921, @thakis wrote:

Reverted this and follow-ups in d763c6e5e2d0a6b34097aa7dabca31e9aff9b0b6 for now.

Sorry this is such a pain to land :(

(See also discussion over in D150688)

I'm not happy that the patch needs to be reverted again.

It has taken me a lot of time to contact all buildbots maintainers to get all buildbots updated to the minimal CMake requirement.
Now that they are updated it turned out that one of the two last updated bots has an issue with this patch and that has been fixed. But now it seems to break Chromium. I don't have access to Windows so I don't know how I can test patches.

Do you have a suggestion how we can move this patch forward?

[thakis]

https://github.com/llvm/llvm-project/issues/62719 is independent of chromium and others have reported problems above too, from what I understand. Is that not accurate?

[Mordante]

In D144509#4349017, @dyung wrote:

I'm not really sure where else to post this, but the pre-merge linux bot still seems to be running 3.18.4.

https://buildkite.com/llvm-project/premerge-checks/builds/152678#018828d2-1837-4fc2-baec-fca595969219

CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.20.0 or higher is required.  You are running version 3.18.4

Thanks, I've notified the owner of the build bot.

[Mordante]

In D144509#4350148, @thakis wrote:

https://github.com/llvm/llvm-project/issues/62719 is independent of chromium and others have reported problems above too, from what I understand. Is that not accurate?

That bug report originally was independent of Chromium, that part was fixed by D150688. This wasn't noticed earlier since that happened on one of the buildbots that took the longest to update. For the earlier failed landings there was never a notification this patch caused issues on Chromium, so I'm quite taken by surprise.

The other issues I see are build errors on Chromium, unless I missed something.

[thakis]

Is https://reviews.llvm.org/D144509#4347562 fixed?

[glandium]

In D144509#4349051, @hans wrote:

In D144509#4347562, @glandium wrote:

FYI, 65429b9af6a2c99d340ab2dcddd41dab201f399c is causing problems on Windows compiler-rt for some reason I haven't identified yet (with cmake 3.25.1). Which suggests for a same version of cmake, this is actually altering its behavior, which I wouldn't have expected...

It is indeed unfortunate that this seems to come with such a fundamental behavior change. (we already have https://github.com/llvm/llvm-project/issues/62719) Do you have a repro for the issue you're seeing?

The Chromium issue that is discussed there is essentially the same thing I was seeing.

[hans]

In D144509#4350052, @Mordante wrote:

In D144509#4349921, @thakis wrote:

Reverted this and follow-ups in d763c6e5e2d0a6b34097aa7dabca31e9aff9b0b6 for now.

Sorry this is such a pain to land :(

(See also discussion over in D150688)

I'm not happy that the patch needs to be reverted again.

It has taken me a lot of time to contact all buildbots maintainers to get all buildbots updated to the minimal CMake requirement.

I sympathize with this, but I still believe reverting in these situations is the right thing to do. It reduces disruption for everyone who needs their builds to keep working, while allowing the failures to be investigated without the pressure of knowing that head is currently broken. That this patch has been hard to land is in the nature of the change itself.

Now that they are updated it turned out that one of the two last updated bots has an issue with this patch and that has been fixed. But now it seems to break Chromium. I don't have access to Windows so I don't know how I can test patches.

I'm happy to test patches on my Windows machine.

Do you have a suggestion how we can move this patch forward?

IIRC, D150688 + the diff in https://github.com/llvm/llvm-project/issues/62719#issuecomment-1552903385 + upgrading the pre-merge linux bot should take care of all known issues.

[Mordante]

In D144509#4356160, @hans wrote:

In D144509#4350052, @Mordante wrote:

In D144509#4349921, @thakis wrote:

Reverted this and follow-ups in d763c6e5e2d0a6b34097aa7dabca31e9aff9b0b6 for now.

Sorry this is such a pain to land :(

(See also discussion over in D150688)

I'm not happy that the patch needs to be reverted again.

It has taken me a lot of time to contact all buildbots maintainers to get all buildbots updated to the minimal CMake requirement.

I sympathize with this, but I still believe reverting in these situations is the right thing to do. It reduces disruption for everyone who needs their builds to keep working, while allowing the failures to be investigated without the pressure of knowing that head is currently broken. That this patch has been hard to land is in the nature of the change itself.

I'm caught quite off-guard that it seems the LLVM buildbots don't cover our Windows support that well. It would also be great to know how we can improve the process to update dependency versions. The current way does not really encourage me to propose LLVM wide updates again.

Now that they are updated it turned out that one of the two last updated bots has an issue with this patch and that has been fixed. But now it seems to break Chromium. I don't have access to Windows so I don't know how I can test patches.

I'm happy to test patches on my Windows machine.

Thanks!

Do you have a suggestion how we can move this patch forward?

IIRC, D150688 + the diff in https://github.com/llvm/llvm-project/issues/62719#issuecomment-1552903385 + upgrading the pre-merge linux bot should take care of all known issues.

Would it make sense to put all these patches in one new review and then test that on Chromium and ask @glandium to test that too. Then we know whether it solves the issues. Do you want me to make a patch or do you want to do it?

[hans]

Do you have a suggestion how we can move this patch forward?

IIRC, D150688 + the diff in https://github.com/llvm/llvm-project/issues/62719#issuecomment-1552903385 + upgrading the pre-merge linux bot should take care of all known issues.

Would it make sense to put all these patches in one new review and then test that on Chromium and ask @glandium to test that too. Then we know whether it solves the issues. Do you want me to make a patch or do you want to do it?

I tested https://github.com/llvm/llvm-project/issues/62719#issuecomment-1552903385 on Chromium already, and that looks good.

[Mordante]

I've created D151344 @glandium @hans @thakis I really would appreciate when you can test the patch locally to avoid another revert round.

bolt/runtime/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 include(CheckIncludeFiles)
 include(GNUInstallDirs)
 
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(CMAKE_CXX_STANDARD 17)
 
 project(libbolt_rt_project)
 

clang/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 # If we are not building as a part of LLVM, build Clang as an
 # standalone project, using LLVM as an external library:
 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(..)
 include(GNUInstallDirs)
 
 if(CLANG_BUILT_STANDALONE)
   set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)

clang/tools/scan-build-py/tests/functional/exec/CMakeLists.txt

 project(exec C)
 
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 include(CheckCCompilerFlag)
 check_c_compiler_flag("-std=c99" C99_SUPPORTED)
 if (C99_SUPPORTED)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99")
 endif()
 
 include(CheckFunctionExists)

compiler-rt/CMakeLists.txt

 # CMake build for CompilerRT.
 #
 # 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 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 # 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")
 
 # Add path for custom compiler-rt modules.
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"

compiler-rt/lib/builtins/CMakeLists.txt

 # This directory contains a large amount of C code which provides
 # generic implementations of the core runtime library along with optimized
 # architecture-specific code in various subdirectories.
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  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()
+  cmake_minimum_required(VERSION 3.20.0)
 
   set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
   project(CompilerRTBuiltins C ASM)
   set(COMPILER_RT_STANDALONE_BUILD TRUE)
   set(COMPILER_RT_BUILTINS_STANDALONE_BUILD TRUE)
 
   set(COMPILER_RT_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../..")
 

compiler-rt/lib/crt/CMakeLists.txt

 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  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()
+  cmake_minimum_required(VERSION 3.20.0)
 
   set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
   project(CompilerRTCRT C)
   set(COMPILER_RT_STANDALONE_BUILD TRUE)
   set(COMPILER_RT_CRT_STANDALONE_BUILD TRUE)
 
   set(COMPILER_RT_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../..")
 

flang/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 set(CMAKE_BUILD_WITH_INSTALL_NAME_DIR ON)

 option(FLANG_ENABLE_WERROR "Fail and stop building flang if a warning is triggered." OFF)
 
 # Check for a standalone build and configure as appropriate from
 # there.
 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()
 
 # Must go below project(..)
 include(GNUInstallDirs)
 
 # MSVC + clang-cl build requires clang_rt.builtin.${target} library

flang/lib/Decimal/CMakeLists.txt

 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.13.4)
+  cmake_minimum_required(VERSION 3.20.0)
 
   project(FortranDecimal C CXX)
 
   set(CMAKE_CXX_STANDARD 17)
   set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
   set(CMAKE_CXX_EXTENSIONS OFF)
 
   set(FLANG_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../..")

flang/runtime/CMakeLists.txt

 #===-- runtime/CMakeLists.txt ----------------------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===------------------------------------------------------------------------===#
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  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()
+  cmake_minimum_required(VERSION 3.20.0)
 
   project(FlangRuntime C CXX)
 
   set(CMAKE_CXX_STANDARD 17)
   set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
   set(CMAKE_CXX_EXTENSIONS OFF)
 
   set(FLANG_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/..")

libc/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 # Default to C++17
 set(CMAKE_CXX_STANDARD 17)
 
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
 
 # The top-level sourse and binary directories.
 set(LIBC_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})

libc/examples/hello_world/CMakeLists.txt

 project(hello_world)
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 include(../examples.cmake)
 
 add_example(
   hello_world
   hello_world.c
 )

libclc/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 project( libclc VERSION 0.2.0 LANGUAGES CXX C)
 
 set(CMAKE_CXX_STANDARD 17)
 
 include( GNUInstallDirs )
 set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS
   amdgcn-amdhsa/lib/SOURCES;

libcxx/CMakeLists.txt

 # See https://libcxx.llvm.org/docs/BuildingLibcxx.html for instructions on how
 # to build libcxx with CMake.
 
 #===============================================================================
 # Setup Project
 #===============================================================================
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"
   "${CMAKE_CURRENT_SOURCE_DIR}/../runtimes/cmake/Modules"

libcxxabi/CMakeLists.txt

 # See www/CMake.html for instructions on how to build libcxxabi with CMake.
 
 #===============================================================================
 # Setup Project
 #===============================================================================
 
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"
   "${CMAKE_CURRENT_SOURCE_DIR}/../runtimes/cmake/Modules"

libunwind/CMakeLists.txt

 #===============================================================================
 # Setup Project
 #===============================================================================
 
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"
   "${CMAKE_CURRENT_SOURCE_DIR}/../runtimes/cmake/Modules"

libunwind/src/CMakeLists.txt

set(LIBUNWIND_ASM_SOURCES
     UnwindRegistersRestore.S
     UnwindRegistersSave.S
     )
 
 # See add_asm_sources() in compiler-rt for explanation of this workaround.
 # 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) OR
-   (${CMAKE_SYSTEM_NAME} MATCHES "AIX"))
+   (MINGW AND CMAKE_VERSION VERSION_LESS 3.17))
   set_source_files_properties(${LIBUNWIND_ASM_SOURCES} PROPERTIES LANGUAGE C)
 endif()
 
 set(LIBUNWIND_HEADERS
     AddressSpace.hpp
     assembly.h
     CompactUnwinder.hpp
     cet_unwind.h

lld/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 # If we are not building as a part of LLVM, build LLD as an
 # standalone project, using LLVM as an external library:
 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(..)
 include(GNUInstallDirs)
 
 if(LLD_BUILT_STANDALONE)
   set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)

lldb/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 # Add path for custom modules.
 set(CMAKE_MODULE_PATH
   ${CMAKE_MODULE_PATH}
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
   )
 
 # If we are not building as part of LLVM, build LLDB as a standalone project,
 # using LLVM as an external library.
 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(..)
 include(GNUInstallDirs)
 
 option(LLDB_INCLUDE_TESTS "Generate build targets for the LLDB unit tests." ${LLVM_INCLUDE_TESTS})
 
 if(LLDB_BUILT_STANDALONE)

lldb/tools/debugserver/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 project(Debugserver LANGUAGES C CXX ASM-ATT)
 
 # Must go below project(..)
 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
     ${CMAKE_MODULE_PATH}
     "${CMAKE_SOURCE_DIR}/../../cmake"
     "${CMAKE_SOURCE_DIR}/../../cmake/modules"
     )
 
   include(LLDBStandalone)

llvm-libgcc/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 if (NOT IS_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/../libunwind")
   message(FATAL_ERROR "llvm-libgcc requires being built in a monorepo layout with libunwind available")
 endif()
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 list(APPEND CMAKE_MODULE_PATH

llvm/CMakeLists.txt

 # See docs/CMake.html for instructions about how to build LLVM with CMake.
 
-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()
+cmake_minimum_required(VERSION 3.20.0)
 
 set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 set(CMAKE_BUILD_WITH_INSTALL_NAME_DIR ON)
 
 if(NOT DEFINED LLVM_VERSION_MAJOR)

llvm/docs/CMake.rst

 .. _Quick start:
 
 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 3.13.4 is the minimum required.
+   CMake. Version 3.20.0 is the minimum required.
 
 #. Open a shell. Your development tools must be reachable from this shell
    through the PATH environment variable.
 
 #. Create a build directory. Building LLVM in the source
    directory is not supported. cd to this directory:
 
    .. code-block:: console

 CMake to develop their own LLVM-based projects against an installed version of
 LLVM regardless of how it was built.
 
 Here is a simple example of a CMakeLists.txt file that imports the LLVM libraries
 and uses them to build a simple application ``simple-tool``.
 
 .. code-block:: cmake
 
-  cmake_minimum_required(VERSION 3.13.4)
+  cmake_minimum_required(VERSION 3.20.0)
   project(SimpleProject)
 
   find_package(LLVM REQUIRED CONFIG)
 
   message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
   message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
 
   # Set your project compile flags.

llvm/docs/GettingStarted.rst

 table below lists those required packages. The Package column is the usual name
 for the software package that LLVM depends on. The Version column provides
 "known to work" versions of the package. The Notes column describes how LLVM
 uses the package and provides other details.
 
 =========================================================== ============ ==========================================
 Package                                                     Version      Notes
 =========================================================== ============ ==========================================
-`CMake <http://cmake.org/>`__                               >=3.13.4     Makefile/workspace generator
+`CMake <http://cmake.org/>`__                               >=3.20.0     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`
 `GNU Make <http://savannah.gnu.org/projects/make>`_         3.79, 3.79.1 Makefile/build processor\ :sup:`4`
 =========================================================== ============ ==========================================
 
 .. note::
 

llvm/docs/ReleaseNotes.rst

.. NOTE
    functionality, or simply have a lot to talk about), see the `NOTE` below
    for adding a new subsection.
 
 * ...
 
 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
 ----------------------
 
 * Typed pointers are no longer supported. See the `opaque pointers
   <OpaquePointers.html>`__ documentation for migration instructions.
 
 * The ``nofpclass`` attribute was introduced. This allows more
   optimizations around special floating point value comparisons.

mlir/CMakeLists.txt

 # MLIR project.
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 # Check if MLIR is built as a standalone project.
 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(..)
 include(GNUInstallDirs)
 set(CMAKE_CXX_STANDARD 17)
 
 if(MLIR_STANDALONE_BUILD)
   find_package(LLVM CONFIG REQUIRED)

mlir/examples/standalone/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 project(standalone-dialect LANGUAGES CXX C)
 
 set(CMAKE_BUILD_WITH_INSTALL_NAME_DIR ON)
 
 set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
 
 find_package(MLIR REQUIRED CONFIG)
 

openmp/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   )
 
 # llvm/runtimes/ will set OPENMP_STANDALONE_BUILD.
 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(..)
 include(GNUInstallDirs)
 
 if (OPENMP_STANDALONE_BUILD)
   # CMAKE_BUILD_TYPE was not set, default to Release.
   if (NOT CMAKE_BUILD_TYPE)

openmp/cmake/DetectTestCompiler/CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 project(DetectTestCompiler C CXX)
 
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 include(CheckIncludeFile)
 include(CheckIncludeFileCXX)
 
 function(write_compiler_information lang)

openmp/docs/SupportAndFAQ.rst

 
 To use this module, simply add the path to CMake's current module path and call
 ``find_package``. The module will be installed with your OpenMP installation by
 default. Including OpenMP offloading support in an application should now only
 require a few additions.
 
 .. code-block:: cmake
 
-  cmake_minimum_required(VERSION 3.13.4)
+  cmake_minimum_required(VERSION 3.20.0)
   project(offloadTest VERSION 1.0 LANGUAGES CXX)
 
   list(APPEND CMAKE_MODULE_PATH "${PATH_TO_OPENMP_INSTALL}/lib/cmake/openmp")
 
   find_package(OpenMPTarget REQUIRED NVPTX)
 
   add_executable(offload)
   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 3.13.4. Supported languages
+Using this module requires at least CMake version 3.20.0. 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.
 
 Q: What does 'Stack size for entry function cannot be statically determined' mean?
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 This is a warning that the Nvidia tools will sometimes emit if the offloading

openmp/libompd/src/CMakeLists.txt

 #
 #//===----------------------------------------------------------------------===//
 #//
 #// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 #// See https://llvm.org/LICENSE.txt for license information.
 #// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #//
 #//===----------------------------------------------------------------------===//
 #
 
 project (libompd)
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 add_library (ompd SHARED TargetValue.cpp omp-debug.cpp omp-state.cpp omp-icv.cpp)
 
 target_link_libraries(ompd omp) # ensure generated import library is created first
 
 set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 
 set(LIBOMPD_LD_STD_FLAGS FALSE CACHE BOOL

openmp/libomptarget/plugins/remote/src/CMakeLists.txt

 ##===----------------------------------------------------------------------===##
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 ##===----------------------------------------------------------------------===##
 #
 # Build a plugin for remote offloading.
 #
 ##===----------------------------------------------------------------------===##
 
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 # Define the suffix for the runtime messaging dumps.
 add_definitions(-DTARGET_NAME=RPC)
 
 include_directories(${LIBOMPTARGET_SRC_DIR})
 include_directories(${LIBOMPTARGET_INCLUDE_DIR})
 include_directories(${GRPC_INCLUDE_DIR})
 include_directories(${RPC_INCLUDE_DIR})

openmp/runtime/cmake/LibompCheckLinkerFlag.cmake

 # There is no real trivial way to do this in CMake, so we implement it here
 # this will have ${boolean} = TRUE if the flag succeeds, otherwise FALSE.
 function(libomp_check_linker_flag flag boolean)
   if(NOT DEFINED "${boolean}")
   set(retval TRUE)
   set(library_source
     "int foo(int a) { return a*a; }")
   set(cmake_source
-    "cmake_minimum_required(VERSION 3.13.4)
+    "cmake_minimum_required(VERSION 3.20.0)
      project(foo C)
      set(CMAKE_SHARED_LINKER_FLAGS \"${flag}\")
      add_library(foo SHARED src_to_link.c)")
   # Compiling as a part of runtimes introduces ARCH-unknown-linux-gnu as a part
   # of a working directory.  So adding a guard for unknown.
   set(failed_regexes "[Ee]rror;[Uu]nknown[^-];[Ss]kipping;LINK : warning;Unsupported command line")
   set(base_dir ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/link_flag_check_${boolean})
   file(MAKE_DIRECTORY ${base_dir})

openmp/tools/Modules/FindOpenMPTarget.cmake

 
 # TODO: Support Fortran
 # TODO: Support multiple offloading targets by setting the "OpenMPTarget" target
 #       to include flags for all components loaded
 # TODO: Configure target architecture without a variable (component NVPTX_SM_70)
 # TODO: Test more compilers
 
 cmake_policy(PUSH)
-cmake_policy(VERSION 3.13.4)
+cmake_policy(VERSION 3.20.0)
 
 find_package(OpenMP ${OpenMPTarget_FIND_VERSION} REQUIRED)
 
 # Find the offloading flags for each compiler.
 function(_OPENMP_TARGET_DEVICE_FLAG_CANDIDATES LANG DEVICE)
   if(NOT OpenMPTarget_${LANG}_FLAGS)
     unset(OpenMPTarget_FLAG_CANDIDATES)
 

openmp/tools/Modules/README.rst

 
 To use this module, simply add the path to CMake's current module path and call
 ``find_package``. The module will be installed with your OpenMP installation by
 default. Including OpenMP offloading support in an application should now only
 require a few additions.
 
 .. code-block:: cmake
 
-  cmake_minimum_required(VERSION 3.13.4)
+  cmake_minimum_required(VERSION 3.20.0)
   project(offloadTest VERSION 1.0 LANGUAGES CXX)
 
   list(APPEND CMAKE_MODULE_PATH "${PATH_TO_OPENMP_INSTALL}/lib/cmake/openmp")
 
   find_package(OpenMPTarget REQUIRED NVPTX)
 
   add_executable(offload)
   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 3.13.4. Supported languages
+Using this module requires at least CMake version 3.20.0. 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
 Clang but this module should work for other compiler vendors such as IBM or GNU.

polly/CMakeLists.txt

 # Check if this is a in tree build.
 if (NOT DEFINED LLVM_MAIN_SRC_DIR)
   project(Polly)
-  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()
+  cmake_minimum_required(VERSION 3.20.0)
   set(POLLY_STANDALONE_BUILD TRUE)
 endif()
 
 # Must go below project(..)
 include(GNUInstallDirs)
 
 if(POLLY_STANDALONE_BUILD)
   # Where is LLVM installed?

pstl/CMakeLists.txt

 #===-- CMakeLists.txt ----------------------------------------------------===##
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===----------------------------------------------------------------------===##
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 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 .*$")
 string(REGEX REPLACE "#define _PSTL_VERSION (.*)$" "\\1" PARALLELSTL_VERSION_SOURCE "${PARALLELSTL_VERSION_SOURCE}")
 math(EXPR VERSION_MAJOR "(${PARALLELSTL_VERSION_SOURCE} / 1000)")
 math(EXPR VERSION_MINOR "((${PARALLELSTL_VERSION_SOURCE} % 1000) / 10)")
 math(EXPR VERSION_PATCH "(${PARALLELSTL_VERSION_SOURCE} % 10)")
 

runtimes/CMakeLists.txt

 # This file handles building LLVM runtime sub-projects.
-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()
+cmake_minimum_required(VERSION 3.20.0)
 project(Runtimes C CXX ASM)
 
 # Add path for custom and the LLVM build's modules to the CMake module path.
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
   "${LLVM_COMMON_CMAKE_UTILS}"