An attempt to abandon omptarget out-of-tree builds.

I want to start using LLVM component libraries in libomptarget
to stop duplicating implementations already available in LLVM
(e.g. LLVMObject, LLVMSupport, etc.). Without relying on LLVM
in all libomptarget builds one has to provide fallback implementation
for each used LLVM feature.

This is an attempt to stop supporting out-of-llvm-tree builds of libomptarget.

I understand that I may need to revert this,
if this affects downstream projects in a bad way.

Differential Revision: https://reviews.llvm.org/D101509

Author: Vyacheslav Zakharin

openmp/CMakeLists.txt

@@ -39,8 +39,6 @@ else()
     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang.exe)
     set(OPENMP_TEST_CXX_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++.exe)
   endif()
-
-  list(APPEND LIBOMPTARGET_LLVM_INCLUDE_DIRS ${LLVM_MAIN_INCLUDE_DIR} ${LLVM_BINARY_DIR}/include)
 endif()
 
 # Check and set up common compiler flags.
@@ -63,20 +61,6 @@ if (APPLE OR WIN32 OR NOT OPENMP_HAVE_STD_CPP14_FLAG)
   set(ENABLE_LIBOMPTARGET OFF)
 endif()
 
-# Attempt to locate LLVM source, required by libomptarget
-if (NOT LIBOMPTARGET_LLVM_INCLUDE_DIRS)
-  if (LLVM_MAIN_INCLUDE_DIR)
-    list(APPEND LIBOMPTARGET_LLVM_INCLUDE_DIRS ${LLVM_MAIN_INCLUDE_DIR})
-  elseif (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/../llvm/include)
-    list(APPEND LIBOMPTARGET_LLVM_INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/../llvm/include)
-  endif()
-endif()
-
-if (NOT LIBOMPTARGET_LLVM_INCLUDE_DIRS)
-  message(STATUS "Missing definition for LIBOMPTARGET_LLVM_INCLUDE_DIRS, disabling libomptarget")
-  set(ENABLE_LIBOMPTARGET OFF)
-endif()
-
 option(OPENMP_ENABLE_LIBOMPTARGET "Enable building libomptarget for offloading."
        ${ENABLE_LIBOMPTARGET})
 option(OPENMP_ENABLE_LIBOMPTARGET_PROFILING "Enable time profiling for libomptarget."

openmp/README.rst

@@ -243,6 +243,15 @@ These flags are **appended**, they do not overwrite any of the preset flags.
 Options for ``libomptarget``
 ----------------------------
 
+An installed LLVM package is a prerequisite for building ``libomptarget``
+library. So ``libomptarget`` may only be built in two cases:
+
+- As a project of a regular LLVM build via **LLVM_ENABLE_PROJECTS**,
+  **LLVM_EXTERNAL_PROJECTS**, or **LLVM_ENABLE_RUNTIMES** or
+- as a standalone project build that uses a pre-installed LLVM package.
+  In this mode one has to make sure that the default CMake
+  ``find_package(LLVM)`` call `succeeds <https://cmake.org/cmake/help/latest/command/find_package.html#search-procedure>`_.
+
 **LIBOMPTARGET_OPENMP_HEADER_FOLDER** = ``""``
   Path of the folder that contains ``omp.h``.  This is required for testing
   out-of-tree builds.

openmp/libomptarget/cmake/Modules/LibomptargetGetDependencies.cmake

@@ -19,6 +19,25 @@
 
 include (FindPackageHandleStandardArgs)
 
+################################################################################
+# Looking for LLVM...
+################################################################################
+
+if (OPENMP_STANDALONE_BUILD)
+  # Complete LLVM package is required for building libomptarget
+  # in an out-of-tree mode.
+  find_package(LLVM REQUIRED)
+  message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
+  message(STATUS "Using LLVM in: ${LLVM_DIR}")
+  list(APPEND LIBOMPTARGET_LLVM_INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
+  list(APPEND CMAKE_MODULE_PATH ${LLVM_CMAKE_DIR})
+  include(AddLLVM)
+else()
+  list(APPEND LIBOMPTARGET_LLVM_INCLUDE_DIRS
+    ${LLVM_MAIN_INCLUDE_DIR} ${LLVM_BINARY_DIR}/include
+    )
+endif()
+
 ################################################################################
 # Looking for libelf...
 ################################################################################
@@ -250,27 +269,4 @@ if (NOT LIBOMPTARGET_CUDA_TOOLKIT_ROOT_DIR_PRESET AND
   endif()
 endif()
 
-if (OPENMP_STANDALONE_BUILD)
-  # This duplicates code from llvm/cmake/config-ix.cmake
-  if( WIN32 AND NOT CYGWIN )
-    # We consider Cygwin as another Unix
-    set(PURE_WINDOWS 1)
-  endif()
-
-  # library checks
-  if( NOT PURE_WINDOWS )
-    check_library_exists(pthread pthread_create "" HAVE_LIBPTHREAD)
-  endif()
-
-  if(HAVE_LIBPTHREAD)
-    # We want to find pthreads library and at the moment we do want to
-    # have it reported as '-l<lib>' instead of '-pthread'.
-    # TODO: switch to -pthread once the rest of the build system can deal with it.
-    set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
-    set(THREADS_HAVE_PTHREAD_ARG Off)
-    find_package(Threads REQUIRED)
-    set(OPENMP_PTHREAD_LIB ${CMAKE_THREAD_LIBS_INIT})
-  endif()
-else()
-  set(OPENMP_PTHREAD_LIB ${LLVM_PTHREAD_LIB})
-endif()
+set(OPENMP_PTHREAD_LIB ${LLVM_PTHREAD_LIB})

openmp/libomptarget/deviceRTLs/amdgcn/CMakeLists.txt

@@ -10,32 +10,6 @@
 #
 ##===----------------------------------------------------------------------===##
 
-find_package(LLVM QUIET CONFIG
-  PATHS
-  $ENV{AOMP}
-  $ENV{HOME}/rocm/aomp
-  /opt/rocm/aomp
-  /usr/lib/rocm/aomp
-  ${LIBOMPTARGET_NVPTX_CUDA_COMPILER_DIR}
-  ${LIBOMPTARGET_NVPTX_CUDA_LINKER_DIR}
-  ${CMAKE_CXX_COMPILER_DIR}
-  NO_DEFAULT_PATH)
-
-if (LLVM_DIR)
-  libomptarget_say("Found LLVM ${LLVM_PACKAGE_VERSION}. Configure: ${LLVM_DIR}/LLVMConfig.cmake")
-else()
-  libomptarget_say("Not building AMDGCN device RTL: AOMP not found")
-  return()
-endif()
-
-set(AOMP_INSTALL_PREFIX ${LLVM_INSTALL_PREFIX})
-
-if (AOMP_INSTALL_PREFIX)
-  set(AOMP_BINDIR ${AOMP_INSTALL_PREFIX}/bin)
-else()
-  set(AOMP_BINDIR ${LLVM_BUILD_BINARY_DIR}/bin)
-endif()
-
 # Copied from nvptx CMakeLists
 if(CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "x86_64")
   set(aux_triple x86_64-unknown-linux-gnu)
@@ -48,7 +22,20 @@ else()
   return()
 endif()
 
-libomptarget_say("Building AMDGCN device RTL. LLVM_COMPILER_PATH=${AOMP_BINDIR}")
+if (LLVM_DIR)
+  # Builds that use pre-installed LLVM have LLVM_DIR set.
+  find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+  find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR}
+    NO_DEFAULT_PATH)
+  find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+  libomptarget_say("Building AMDGCN device RTL. Using clang: ${CLANG_TOOL}")
+else()
+  # LLVM in-tree builds may use CMake target names to discover the tools.
+  set(CLANG_TOOL $<TARGET_FILE:clang>)
+  set(LINK_TOOL $<TARGET_FILE:llvm-link>)
+  set(OPT_TOOL $<TARGET_FILE:opt>)
+  libomptarget_say("Building AMDGCN device RTL. Using clang from in-tree build")
+endif()
 
 project(omptarget-amdgcn)
 
@@ -109,7 +96,7 @@ if (DEFINED LIBOMPTARGET_AMDGCN_GFXLIST)
 endif()
 
 macro(add_cuda_bc_library)
-  set(cu_cmd ${AOMP_BINDIR}/clang++
+  set(cu_cmd ${CLANG_TOOL}
     -xc++
     -c
     -std=c++14
@@ -145,7 +132,7 @@ macro(add_cuda_bc_library)
 
   add_custom_command(
     OUTPUT linkout.cuda.${mcpu}.bc
-    COMMAND ${AOMP_BINDIR}/llvm-link ${bc1_files} -o linkout.cuda.${mcpu}.bc
+    COMMAND ${LINK_TOOL} ${bc1_files} -o linkout.cuda.${mcpu}.bc
     DEPENDS ${bc1_files})
 
   list(APPEND bc_files linkout.cuda.${mcpu}.bc)
@@ -160,7 +147,7 @@ foreach(mcpu ${mcpus})
   set(bc_libname lib${libname}-${mcpu}.bc)
   add_custom_command(
     OUTPUT ${bc_libname}
-    COMMAND ${AOMP_BINDIR}/llvm-link ${bc_files} | ${AOMP_BINDIR}/opt --always-inline -o ${OUTPUTDIR}/${bc_libname}
+    COMMAND ${LINK_TOOL} ${bc_files} | ${OPT_TOOL} --always-inline -o ${OUTPUTDIR}/${bc_libname}
     DEPENDS ${bc_files})
 
   add_custom_target(lib${libname}-${mcpu} ALL DEPENDS ${bc_libname})

openmp/libomptarget/src/CMakeLists.txt

@@ -24,29 +24,19 @@ set(LIBOMPTARGET_SRC_FILES ${LIBOMPTARGET_SRC_FILES} PARENT_SCOPE)
 
 include_directories(${LIBOMPTARGET_LLVM_INCLUDE_DIRS})
 
-# Build libomptarget library with libdl dependency. Add LLVMSupport
-# dependency if building in-tree with profiling enabled.
-if(OPENMP_STANDALONE_BUILD OR (NOT OPENMP_ENABLE_LIBOMPTARGET_PROFILING))
-  add_library(omptarget SHARED ${LIBOMPTARGET_SRC_FILES})
-  target_link_libraries(omptarget
-    ${CMAKE_DL_LIBS}
-    "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/exports")
-else()
-  set(LLVM_LINK_COMPONENTS
-    Support
-    )
-  add_llvm_library(omptarget SHARED ${LIBOMPTARGET_SRC_FILES}
-      LINK_LIBS ${CMAKE_DL_LIBS}
-      "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/exports"
-      )
+# Build libomptarget library with libdl dependency.
+add_library(omptarget SHARED ${LIBOMPTARGET_SRC_FILES})
+if (OPENMP_ENABLE_LIBOMPTARGET_PROFILING)
+  # Add LLVMSupport dependency if profiling is enabled.
+  # Linking with LLVM component libraries also requires
+  # aligning the compile flags.
+  llvm_update_compile_flags(omptarget)
   target_compile_definitions(omptarget PUBLIC OMPTARGET_PROFILE_ENABLED)
+  target_link_libraries(omptarget PRIVATE LLVMSupport)
 endif()
-
-# libomptarget needs to be set separately because add_llvm_library doesn't
-# conform with location configuration of its parent scope.
-set_target_properties(omptarget
-  PROPERTIES
-  LIBRARY_OUTPUT_DIRECTORY ${LIBOMPTARGET_LIBRARY_DIR})
+target_link_libraries(omptarget PRIVATE
+  ${CMAKE_DL_LIBS}
+  "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/exports")
 
 # Install libomptarget under the lib destination folder.
 install(TARGETS omptarget LIBRARY COMPONENT omptarget