[flang][runtime] Allow building CUDA PTX library without global vars definitions. (#90280)

Author: vzakhari

flang/cmake/modules/AddFlangOffloadRuntime.cmake

@@ -2,6 +2,10 @@ option(FLANG_EXPERIMENTAL_CUDA_RUNTIME
   "Compile Fortran runtime as CUDA sources (experimental)" OFF
   )
 
+option(FLANG_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS
+  "Do not compile global variables' definitions when producing PTX library" OFF
+  )
+
 set(FLANG_LIBCUDACXX_PATH "" CACHE PATH "Path to libcu++ package installation")
 
 set(FLANG_EXPERIMENTAL_OMP_OFFLOAD_BUILD "off" CACHE STRING
@@ -56,6 +60,11 @@ macro(enable_cuda_compilation name files)
     # Add an OBJECT library consisting of CUDA PTX.
     llvm_add_library(${name}PTX OBJECT PARTIAL_SOURCES_INTENDED ${files})
     set_property(TARGET obj.${name}PTX PROPERTY CUDA_PTX_COMPILATION ON)
+    if (FLANG_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS)
+      target_compile_definitions(obj.${name}PTX
+        PRIVATE FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+        )
+    endif()
   endif()
 endmacro()
 

flang/runtime/environment.cpp

@@ -23,9 +23,11 @@ extern char **environ;
 
 namespace Fortran::runtime {
 
+#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
 RT_OFFLOAD_VAR_GROUP_BEGIN
 RT_VAR_ATTRS ExecutionEnvironment executionEnvironment;
 RT_OFFLOAD_VAR_GROUP_END
+#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
 
 static void SetEnvironmentDefaults(const EnvironmentDefaultList *envDefaults) {
   if (!envDefaults) {

flang/runtime/unit.cpp

@@ -19,11 +19,13 @@
 
 namespace Fortran::runtime::io {
 
+#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
 RT_OFFLOAD_VAR_GROUP_BEGIN
 RT_VAR_ATTRS ExternalFileUnit *defaultInput{nullptr}; // unit 5
 RT_VAR_ATTRS ExternalFileUnit *defaultOutput{nullptr}; // unit 6
 RT_VAR_ATTRS ExternalFileUnit *errorOutput{nullptr}; // unit 0 extension
 RT_OFFLOAD_VAR_GROUP_END
+#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 

flang/runtime/utf.cpp

@@ -10,6 +10,7 @@
 
 namespace Fortran::runtime {
 
+#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
 // clang-format off
 RT_OFFLOAD_VAR_GROUP_BEGIN
 const RT_CONST_VAR_ATTRS std::uint8_t UTF8FirstByteTable[256]{
@@ -40,6 +41,7 @@ const RT_CONST_VAR_ATTRS std::uint8_t UTF8FirstByteTable[256]{
 };
 RT_OFFLOAD_VAR_GROUP_END
 // clang-format on
+#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 // Non-minimal encodings are accepted.