[MLIR] Removes CMake work-arounds.

[Mordante]

Summary

CMake older than 3.20.0 is no longer supported.
This removes work-arounds for no longer supported versions.

[h-vetinari]

mlir/tools/mlir-vulkan-runner/CMakeLists.txt

16–17

[h-vetinari]

mlir/cmake/modules/MLIRDetectPythonEnv.cmake

14–19

Not sure if removing mentions of old CMake is in scope as well. There may occasionally be a good reason to keep such comments, but it does pollute the search results when looking for old CMake

[h-vetinari]

Two more mentions of old CMake in https://github.com/llvm/llvm-project/blob/main/mlir/lib/Dialect/SparseTensor/IR/CMakeLists.txt

[Mordante]

In D152101#4397725, @h-vetinari wrote:

Two more mentions of old CMake in https://github.com/llvm/llvm-project/blob/main/mlir/lib/Dialect/SparseTensor/IR/CMakeLists.txt

I feel changing this is out of scope. I agree it would be nice to fix this, but I will not pursue it. Feel free to provide patches for these improvements.

[Mordante]

mlir/cmake/modules/MLIRDetectPythonEnv.cmake

14–19

I prefer to leave that cleanup to the MLIR maintainers. They might have intended to to more than just removing the comment.

mlir/cmake/modules/MLIRDetectPythonEnv.cmake

 # Macros and functions related to detecting details of the Python environment.
 
 # Finds and configures python packages needed to build MLIR Python bindings.
 macro(mlir_configure_python_dev_packages)
-  if(CMAKE_VERSION VERSION_LESS "3.19.0")
-  message(SEND_ERROR
-      "Building MLIR Python bindings is known to rely on CMake features "
-      "that require at least version 3.19. Recommend upgrading to 3.19+ "
-      "for full support. Detected current version: ${CMAKE_VERSION}")
-  endif()
-
   if(MLIR_DETECT_PYTHON_ENV_PRIME_SEARCH)
     # Prime the search for python to see if there is a full development
     # package. This seems to work around cmake bugs searching only for
     # Development.Module in some environments. However, in other environments
     # it may interfere with the subsequent search for Development.Module.
     find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION}
       COMPONENTS Interpreter Development)
   endif()
 
   # After CMake 3.18, we are able to limit the scope of the search to just
   # Development.Module. Searching for Development will fail in situations where
   # the Python libraries are not available. When possible, limit to just
   # Development.Module.
   # See https://pybind11.readthedocs.io/en/stable/compiling.html#findpython-mode
   set(_python_development_component Development.Module)
 
   find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION}
     COMPONENTS Interpreter ${_python_development_component} NumPy REQUIRED)
   unset(_python_development_component)
   message(STATUS "Found python include dirs: ${Python3_INCLUDE_DIRS}")
   message(STATUS "Found python libraries: ${Python3_LIBRARIES}")
   message(STATUS "Found numpy v${Python3_NumPy_VERSION}: ${Python3_NumPy_INCLUDE_DIRS}")
   mlir_detect_pybind11_install()

mlir/tools/mlir-vulkan-runner/CMakeLists.txt

 set(LLVM_OPTIONAL_SOURCES
   mlir-vulkan-runner.cpp
   vulkan-runtime-wrappers.cpp
   VulkanRuntime.cpp
   VulkanRuntime.h
   )
 
 if (MLIR_ENABLE_VULKAN_RUNNER)
   message(STATUS "Building the Vulkan runner")
 
-  # At first try "FindVulkan" from:
-  # https://cmake.org/cmake/help/v3.7/module/FindVulkan.html
-  if (NOT CMAKE_VERSION VERSION_LESS 3.7.0)
-    find_package(Vulkan)
-  endif()
 
   # If Vulkan is not found try a path specified by VULKAN_SDK.
   if (NOT Vulkan_FOUND)
     if ("$ENV{VULKAN_SDK}" STREQUAL "")
-      message(FATAL_ERROR "Please use at least CMAKE 3.7.0 or provide "
+      message(FATAL_ERROR "Vulkan not found through CMake; please provide "
                           "VULKAN_SDK path as an environment variable")
     endif()
 
     find_library(Vulkan_LIBRARY vulkan HINTS "$ENV{VULKAN_SDK}/lib" REQUIRED)
     if (Vulkan_LIBRARY)
       set(Vulkan_FOUND ON)
       set(Vulkan_INCLUDE_DIR "$ENV{VULKAN_SDK}/include")
       message(STATUS "Found Vulkan: " ${Vulkan_LIBRARY})
     endif()