[OpenMP] Disabled profiling in `libomp` by default to unblock link errors

Link error occurred when time profiling in libomp is enabled by default
because `libomp` is assumed to be a C library but the dependence on
`libLLVMSupport` for profiling is a C++ library. Currently the issue blocks all
OpenMP tests in Phabricator.

This patch set a new CMake option `OPENMP_ENABLE_LIBOMP_PROFILING` to
enable/disable the feature. By default it is disabled. Note that once time
profiling is enabled for `libomp`, it becomes a C++ library.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D95585

(cherry picked from commit c571b168349fdf22d1dc8b920bcffa3d5161f0a2)

6 files changed, 29 insertions, 10 deletions

diff --git a/openmp/CMakeLists.txt b/openmp/CMakeLists.txt
index 67600bebdafb..4787d4b5a321 100644
--- a/openmp/CMakeLists.txt
+++ b/openmp/CMakeLists.txt
@@ -86,6 +86,12 @@ option(OPENMP_ENABLE_LIBOMPTARGET "Enable building libomptarget for offloading."
        ${ENABLE_LIBOMPTARGET})
 option(OPENMP_ENABLE_LIBOMPTARGET_PROFILING "Enable time profiling for libomptarget."
        ${ENABLE_LIBOMPTARGET})
+option(OPENMP_ENABLE_LIBOMP_PROFILING "Enable time profiling for libomp." OFF)
+
+# Build host runtime library, after LIBOMPTARGET variables are set since they are needed
+# to enable time profiling support in the OpenMP runtime.
+add_subdirectory(runtime)
+
 if (OPENMP_ENABLE_LIBOMPTARGET)
   # Check that the library can actually be built.
   if (APPLE OR WIN32)
diff --git a/openmp/docs/design/Runtimes.rst b/openmp/docs/design/Runtimes.rst
index 016b88ba324b..ad36e43eccdc 100644
--- a/openmp/docs/design/Runtimes.rst
+++ b/openmp/docs/design/Runtimes.rst
@@ -48,7 +48,10 @@ similar to Clang's ``-ftime-trace`` option. This generates a JSON file based on
 `Speedscope App`_. Building this feature depends on the `LLVM Support Library`_
 for time trace output. Using this library is enabled by default when building
 using the CMake option ``OPENMP_ENABLE_LIBOMPTARGET_PROFILING``. The output will
-be saved to the filename specified by the environment variable.
+be saved to the filename specified by the environment variable. For multi-threaded
+applications, profiling in ``libomp`` is also needed. Setting the CMake option
+``OPENMP_ENABLE_LIBOMP_PROFILING=ON`` to enable the feature. Note that this will
+turn ``libomp`` into a C++ library.
 
 .. _`Chrome Tracing`: https://www.chromium.org/developers/how-tos/trace-event-profiling-tool
 
diff --git a/openmp/runtime/CMakeLists.txt b/openmp/runtime/CMakeLists.txt
index 9fdd04f41646..8828ff8ef455 100644
--- a/openmp/runtime/CMakeLists.txt
+++ b/openmp/runtime/CMakeLists.txt
@@ -34,7 +34,6 @@ if(${OPENMP_STANDALONE_BUILD})
   # Should assertions be enabled?  They are on by default.
   set(LIBOMP_ENABLE_ASSERTIONS TRUE CACHE BOOL
     "enable assertions?")
-  set(LIBOMPTARGET_PROFILING_SUPPORT FALSE)
 else() # Part of LLVM build
   # Determine the native architecture from LLVM.
   string(TOLOWER "${LLVM_TARGET_ARCH}" LIBOMP_NATIVE_ARCH)
@@ -66,10 +65,11 @@ else() # Part of LLVM build
     libomp_get_architecture(LIBOMP_ARCH)
   endif ()
   set(LIBOMP_ENABLE_ASSERTIONS ${LLVM_ENABLE_ASSERTIONS})
-  # Time profiling support
-  set(LIBOMPTARGET_PROFILING_SUPPORT ${OPENMP_ENABLE_LIBOMPTARGET_PROFILING})
 endif()
 
+# Time profiling support
+set(LIBOMP_PROFILING_SUPPORT ${OPENMP_ENABLE_LIBOMP_PROFILING})
+
 # FUJITSU A64FX is a special processor because its cache line size is 256.
 # We need to pass this information into kmp_config.h.
 if(LIBOMP_ARCH STREQUAL "aarch64")
diff --git a/openmp/runtime/src/CMakeLists.txt b/openmp/runtime/src/CMakeLists.txt
index 2e927df84f5c..822f9ca2b825 100644
--- a/openmp/runtime/src/CMakeLists.txt
+++ b/openmp/runtime/src/CMakeLists.txt
@@ -50,6 +50,14 @@ if(${LIBOMP_USE_HWLOC})
   include_directories(${LIBOMP_HWLOC_INSTALL_DIR}/include)
 endif()
 
+# Building with time profiling support requires LLVM directory includes.
+if(LIBOMP_PROFILING_SUPPORT)
+  include_directories(
+    ${LLVM_MAIN_INCLUDE_DIR}
+    ${LLVM_INCLUDE_DIR}
+  )
+endif()
+
 # Getting correct source files to build library
 set(LIBOMP_CXXFILES)
 set(LIBOMP_ASMFILES)
@@ -135,7 +143,7 @@ libomp_get_ldflags(LIBOMP_CONFIGURED_LDFLAGS)
 
 libomp_get_libflags(LIBOMP_CONFIGURED_LIBFLAGS)
 # Build libomp library. Add LLVMSupport dependency if building in-tree with libomptarget profiling enabled.
-if(OPENMP_STANDALONE_BUILD OR (NOT OPENMP_ENABLE_LIBOMPTARGET_PROFILING))
+if(OPENMP_STANDALONE_BUILD OR (NOT OPENMP_ENABLE_LIBOMP_PROFILING))
   add_library(omp ${LIBOMP_LIBRARY_KIND} ${LIBOMP_SOURCE_FILES})
   # Linking command will include libraries in LIBOMP_CONFIGURED_LIBFLAGS
   target_link_libraries(omp ${LIBOMP_CONFIGURED_LIBFLAGS} ${CMAKE_DL_LIBS})
@@ -144,6 +152,8 @@ else()
     LINK_LIBS ${LIBOMP_CONFIGURED_LIBFLAGS} ${CMAKE_DL_LIBS}
     LINK_COMPONENTS Support
     )
+  # libomp must be a C++ library such that it can link libLLVMSupport
+  set(LIBOMP_LINKER_LANGUAGE CXX)
 endif()
 
 set_target_properties(omp PROPERTIES
diff --git a/openmp/runtime/src/kmp_config.h.cmake b/openmp/runtime/src/kmp_config.h.cmake
index 3d682c690fc7..f6aee7197ee8 100644
--- a/openmp/runtime/src/kmp_config.h.cmake
+++ b/openmp/runtime/src/kmp_config.h.cmake
@@ -44,8 +44,8 @@
 #define OMPT_DEBUG LIBOMP_OMPT_DEBUG
 #cmakedefine01 LIBOMP_OMPT_SUPPORT
 #define OMPT_SUPPORT LIBOMP_OMPT_SUPPORT
-#cmakedefine01 LIBOMPTARGET_PROFILING_SUPPORT
-#define OMPTARGET_PROFILING_SUPPORT LIBOMPTARGET_PROFILING_SUPPORT
+#cmakedefine01 LIBOMP_PROFILING_SUPPORT
+#define OMP_PROFILING_SUPPORT LIBOMP_PROFILING_SUPPORT
 #cmakedefine01 LIBOMP_OMPT_OPTIONAL
 #define OMPT_OPTIONAL LIBOMP_OMPT_OPTIONAL
 #cmakedefine01 LIBOMP_USE_ADAPTIVE_LOCKS
diff --git a/openmp/runtime/src/kmp_runtime.cpp b/openmp/runtime/src/kmp_runtime.cpp
index 4a0634d59cff..a6e32bd008e1 100644
--- a/openmp/runtime/src/kmp_runtime.cpp
+++ b/openmp/runtime/src/kmp_runtime.cpp
@@ -32,7 +32,7 @@
 #include "ompt-specific.h"
 #endif
 
-#if OMPTARGET_PROFILING_SUPPORT
+#if OMP_PROFILING_SUPPORT
 #include "llvm/Support/TimeProfiler.h"
 static char *ProfileTraceFile = nullptr;
 #endif
@@ -5740,7 +5740,7 @@ void __kmp_free_thread(kmp_info_t *this_th) {
 /* ------------------------------------------------------------------------ */
 
 void *__kmp_launch_thread(kmp_info_t *this_thr) {
-#if OMPTARGET_PROFILING_SUPPORT
+#if OMP_PROFILING_SUPPORT
   ProfileTraceFile = getenv("LIBOMPTARGET_PROFILE");
   // TODO: add a configuration option for time granularity
   if (ProfileTraceFile)
@@ -5848,7 +5848,7 @@ void *__kmp_launch_thread(kmp_info_t *this_thr) {
   KA_TRACE(10, ("__kmp_launch_thread: T#%d done\n", gtid));
   KMP_MB();
 
-#if OMPTARGET_PROFILING_SUPPORT
+#if OMP_PROFILING_SUPPORT
   llvm::timeTraceProfilerFinishThread();
 #endif
   return this_thr;