[llvm] [openmp] [Offload] Correctly reject building on unsupported architectures (PR #92276)

[Joseph Huber via llvm-commits]

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@@ -17,26 +17,16 @@ if ("${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
   project(offload C CXX ASM)
 endif()
 
-set(ENABLE_LIBOMPTARGET ON)
-# Currently libomptarget cannot be compiled on Windows or MacOS X.
-# Since the device plugins are only supported on Linux anyway,
-# there is no point in trying to compile libomptarget on other OSes.
-# 32-bit systems are not supported either.
-if (APPLE OR WIN32 OR NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES OR NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
-  set(ENABLE_LIBOMPTARGET OFF)
-endif()
-
-option(OPENMP_ENABLE_LIBOMPTARGET "Enable building libomptarget for offloading."
-       ${ENABLE_LIBOMPTARGET})
-if (OPENMP_ENABLE_LIBOMPTARGET)
-  # Check that the library can actually be built.
-  if (APPLE OR WIN32)
-    message(FATAL_ERROR "libomptarget cannot be built on Windows and MacOS X!")
-  elseif (NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
-    message(FATAL_ERROR "Host compiler must support C++17 to build libomptarget!")
-  elseif (NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
-    message(FATAL_ERROR "libomptarget on 32-bit systems are not supported!")
-  endif()
+# Check that the library can actually be built.
+if(APPLE OR WIN32 OR WASM)
+  message(WARNING "libomptarget cannot be built on Windows and MacOS X!")
+  return()
+elseif(NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+  message(WARNING "Host compiler must support C++17 to build libomptarget!")
+  return()
+elseif(NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
+  message(WARNING "libomptarget on 32-bit systems are not yet supported!")
----------------
jhuber6 wrote:

It's theoretically possible to implement, since maybe some day someone will have a use-case for it. But since there's no active plans for it I suppose it's best to keep it simple.

https://github.com/llvm/llvm-project/pull/92276