[Libomptarget] Rework interface for enabling plugins (#86875)

Summary:
Previously we would build all of the plugins by default and then only
load some using the `LIBOMPTARGET_PLUGINS_TO_LOAD` variable. This patch
renamed this to `LIBOMPTARGET_PLUGINS_TO_BUILD` and changes whether or
not it will include the plugin in CMake.

Additionally this patch creates a new `Targets.def` file that allows us
to enumerate all of the enabled plugins. This is somewhat different from
the old method, and it's done this way for future use that will need to
be shared. This follows the same method that LLVM uses for its targets,
however it does require adding an extra include path.

Depends on https://github.com/llvm/llvm-project/pull/86868

6 files changed, 64 insertions, 32 deletions

diff --git a/offload/CMakeLists.txt b/offload/CMakeLists.txt
index abc8baa..a416ac2 100644
--- a/offload/CMakeLists.txt
+++ b/offload/CMakeLists.txt
@@ -151,6 +151,25 @@ if (NOT LIBOMPTARGET_LLVM_INCLUDE_DIRS)
   message(FATAL_ERROR "Missing definition for LIBOMPTARGET_LLVM_INCLUDE_DIRS")
 endif()
 
+set(LIBOMPTARGET_ALL_PLUGIN_TARGETS amdgpu cuda host)
+set(LIBOMPTARGET_PLUGINS_TO_BUILD "all" CACHE STRING
+    "Semicolon-separated list of plugins to use: cuda, amdgpu, host or \"all\".")
+
+if(LIBOMPTARGET_PLUGINS_TO_BUILD STREQUAL "all")
+  set(LIBOMPTARGET_PLUGINS_TO_BUILD ${LIBOMPTARGET_ALL_PLUGIN_TARGETS})
+endif()
+
+set(LIBOMPTARGET_ENUM_PLUGIN_TARGETS "")
+foreach(plugin IN LISTS LIBOMPTARGET_PLUGINS_TO_BUILD)
+  set(LIBOMPTARGET_ENUM_PLUGIN_TARGETS
+      "${LIBOMPTARGET_ENUM_PLUGIN_TARGETS}PLUGIN_TARGET(${plugin})\n")
+endforeach()
+string(STRIP ${LIBOMPTARGET_ENUM_PLUGIN_TARGETS} LIBOMPTARGET_ENUM_PLUGIN_TARGETS)
+configure_file(
+  ${CMAKE_CURRENT_SOURCE_DIR}/include/Shared/Targets.def.in
+  ${CMAKE_CURRENT_BINARY_DIR}/include/Shared/Targets.def
+)
+
 include_directories(${LIBOMPTARGET_LLVM_INCLUDE_DIRS})
 
 # This is a list of all the targets that are supported/tested right now.
@@ -288,6 +307,7 @@ set(LIBOMPTARGET_GPU_LIBC_SUPPORT ${LLVM_LIBC_GPU_BUILD} CACHE BOOL
 pythonize_bool(LIBOMPTARGET_GPU_LIBC_SUPPORT)
 
 set(LIBOMPTARGET_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/include)
+set(LIBOMPTARGET_BINARY_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
 message(STATUS "OpenMP tools dir in libomptarget: ${LIBOMP_OMP_TOOLS_INCLUDE_DIR}")
 if(LIBOMP_OMP_TOOLS_INCLUDE_DIR)
   include_directories(${LIBOMP_OMP_TOOLS_INCLUDE_DIR})
diff --git a/offload/include/Shared/Targets.def.in b/offload/include/Shared/Targets.def.in
new file mode 100644
index 0000000..f34b523
--- /dev/null
+++ b/offload/include/Shared/Targets.def.in
@@ -0,0 +1,20 @@
+//===-- Shared/Targets.def - Target plugin enumerator -----------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Enumerates over all of the supported target plugins that are available to
+// the offloading library.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef PLUGIN_TARGET
+#  error Please define the macro PLUGIN_TARGET(TargetName)
+#endif
+
+@LIBOMPTARGET_ENUM_PLUGIN_TARGETS@
+
+#undef PLUGIN_TARGET
diff --git a/offload/plugins-nextgen/CMakeLists.txt b/offload/plugins-nextgen/CMakeLists.txt
index dbd82ac..df625e9 100644
--- a/offload/plugins-nextgen/CMakeLists.txt
+++ b/offload/plugins-nextgen/CMakeLists.txt
@@ -69,9 +69,12 @@ function(add_target_library target_name lib_name)
   set_target_properties(${target_name} PROPERTIES CXX_VISIBILITY_PRESET protected)
 endfunction()
 
-add_subdirectory(amdgpu)
-add_subdirectory(cuda)
-add_subdirectory(host)
+foreach(plugin IN LISTS LIBOMPTARGET_PLUGINS_TO_BUILD)
+  if(NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${plugin})
+    message(FATAL_ERROR "Unknown plugin target '${plugin}'")
+  endif()
+  add_subdirectory(${plugin})
+endforeach()
 
 # Make sure the parent scope can see the plugins that will be created.
 set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
diff --git a/offload/plugins-nextgen/common/CMakeLists.txt b/offload/plugins-nextgen/common/CMakeLists.txt
index a7350e6..acf0af6 100644
--- a/offload/plugins-nextgen/common/CMakeLists.txt
+++ b/offload/plugins-nextgen/common/CMakeLists.txt
@@ -62,6 +62,7 @@ target_link_options(PluginCommon PUBLIC ${offload_link_flags})
 target_include_directories(PluginCommon PUBLIC 
   ${CMAKE_CURRENT_SOURCE_DIR}/include
   ${LIBOMPTARGET_LLVM_INCLUDE_DIRS}
+  ${LIBOMPTARGET_BINARY_INCLUDE_DIR}
   ${LIBOMPTARGET_INCLUDE_DIR}
 )
 
diff --git a/offload/src/CMakeLists.txt b/offload/src/CMakeLists.txt
index 8b7be98..eda5a85 100644
--- a/offload/src/CMakeLists.txt
+++ b/offload/src/CMakeLists.txt
@@ -37,6 +37,7 @@ add_llvm_library(omptarget
 
   ADDITIONAL_HEADER_DIRS
   ${LIBOMPTARGET_INCLUDE_DIR}
+  ${LIBOMPTARGET_BINARY_INCLUDE_DIR}
 
   LINK_COMPONENTS
   Support
@@ -49,7 +50,9 @@ add_llvm_library(omptarget
   NO_INSTALL_RPATH
   BUILDTREE_ONLY
 )
-target_include_directories(omptarget PRIVATE ${LIBOMPTARGET_INCLUDE_DIR})
+target_include_directories(omptarget PRIVATE 
+  ${LIBOMPTARGET_INCLUDE_DIR} ${LIBOMPTARGET_BINARY_INCLUDE_DIR}
+)
 
 if (LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
   target_link_libraries(omptarget PRIVATE
@@ -65,20 +68,6 @@ target_compile_definitions(omptarget PRIVATE
 target_compile_options(omptarget PUBLIC ${offload_compile_flags})
 target_link_options(omptarget PUBLIC ${offload_link_flags})
 
-macro(check_plugin_target target)
-if (TARGET omptarget.rtl.${target})
-	list(APPEND LIBOMPTARGET_PLUGINS_TO_LOAD ${target})
-endif()
-endmacro()
-
-set(LIBOMPTARGET_PLUGINS_TO_LOAD "" CACHE STRING
-  "Comma separated list of plugin names to look for at runtime")
-if (NOT LIBOMPTARGET_PLUGINS_TO_LOAD)
-	check_plugin_target(cuda)
-	check_plugin_target(amdgpu)
-	check_plugin_target(host)
-endif()
-
 list(TRANSFORM LIBOMPTARGET_PLUGINS_TO_LOAD PREPEND "\"libomptarget.rtl.")
 list(TRANSFORM LIBOMPTARGET_PLUGINS_TO_LOAD APPEND "\"")
 list(JOIN LIBOMPTARGET_PLUGINS_TO_LOAD "," ENABLED_OFFLOAD_PLUGINS)
diff --git a/offload/src/PluginManager.cpp b/offload/src/PluginManager.cpp
index 792cae3..dbb556c 100644
--- a/offload/src/PluginManager.cpp
+++ b/offload/src/PluginManager.cpp
@@ -23,9 +23,6 @@ using namespace llvm::sys;
 
 PluginManager *PM = nullptr;
 
-// List of all plugins that can support offloading.
-static const char *RTLNames[] = {ENABLED_OFFLOAD_PLUGINS};
-
 Expected<std::unique_ptr<PluginAdaptorTy>>
 PluginAdaptorTy::create(const std::string &Name) {
   DP("Attempting to load library '%s'...\n", Name.c_str());
@@ -95,17 +92,19 @@ void PluginManager::init() {
 
   // Attempt to open all the plugins and, if they exist, check if the interface
   // is correct and if they are supporting any devices.
-  for (const char *Name : RTLNames) {
-    auto PluginAdaptorOrErr =
-        PluginAdaptorTy::create(std::string(Name) + ".so");
-    if (!PluginAdaptorOrErr) {
-      [[maybe_unused]] std::string InfoMsg =
-          toString(PluginAdaptorOrErr.takeError());
-      DP("%s", InfoMsg.c_str());
-    } else {
-      PluginAdaptors.push_back(std::move(*PluginAdaptorOrErr));
-    }
-  }
+#define PLUGIN_TARGET(Name)                                                    \
+  do {                                                                         \
+    auto PluginAdaptorOrErr =                                                  \
+        PluginAdaptorTy::create("libomptarget.rtl." #Name ".so");              \
+    if (!PluginAdaptorOrErr) {                                                 \
+      [[maybe_unused]] std::string InfoMsg =                                   \
+          toString(PluginAdaptorOrErr.takeError());                            \
+      DP("%s", InfoMsg.c_str());                                               \
+    } else {                                                                   \
+      PluginAdaptors.push_back(std::move(*PluginAdaptorOrErr));                \
+    }                                                                          \
+  } while (false);
+#include "Shared/Targets.def"
 
   DP("RTLs loaded!\n");
 }