[gomp4 02/14] nvptx: emit pointers to OpenMP target region entry points

[Alexander Monakov <amonakov at ispras dot ru>]

Note: this patch will have to be more complex if we go with 'approach 2'
described in a later patch, 07/14 "launch target functions via gomp_nvptx_main".

For OpenMP offloading, libgomp invokes 'gomp_nvptx_main' as the accelerator
kernel, passing it a pointer to outlined target region function.  That
function needs to be a device function (.func rather than .kernel), unless we
want to bump the GPU requirement from sm_30 to sm_35.  To retrieve the device
function pointer from the host side, we need to emit a global-visibility
pointer to that function in PTX.  The naming scheme for deriving the pointer
name based on function name is an ABI item between the backend and libgomp
plugin.

	* config/nvptx/nvptx.c: (write_libgomp_anchor): New.  Use it...
        (nvptx_declare_function_name): ...here to emit pointers for libgomp.
---
 gcc/config/nvptx/nvptx.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index df7b61f..a619e4c 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -657,6 +657,26 @@ nvptx_init_axis_predicate (FILE *file, int regno, const char *name)
   fprintf (file, "\t}\n");
 }
 
+/* For function DECL outlined for an OpenMP 'target' region, emit a global
+   pointer: void *__ptr_NAME = NAME; to be used in libgomp nvptx plugin.  */
+
+static void
+write_libgomp_anchor (std::stringstream &s, const char *name, const_tree decl)
+{
+  if (!lookup_attribute ("omp target entrypoint", DECL_ATTRIBUTES (decl)))
+    return;
+
+  /* OpenMP target regions are entered via gomp_nvptx_main.  */
+  static bool gomp_nvptx_main_declared;
+  if (!gomp_nvptx_main_declared)
+    {
+      gomp_nvptx_main_declared = true;
+      s << "// BEGIN GLOBAL FUNCTION DECL: gomp_nvptx_main\n";
+    }
+  s << ".visible .global " << nvptx_ptx_type_from_mode (Pmode, false);
+  s << " __ptr_" << name << " = " << name << ";\n";
+}
+
 /* Implement ASM_DECLARE_FUNCTION_NAME.  Writes the start of a ptx
    function, including local var decls and copies from the arguments to
    local regs.  */
@@ -671,6 +691,8 @@ nvptx_declare_function_name (FILE *file, const char *name, const_tree decl)
 
   std::stringstream s;
   write_function_decl_and_comment (s, name, decl);
+  if (flag_openmp)
+    write_libgomp_anchor (s, name, decl);
   s << "// BEGIN";
   if (TREE_PUBLIC (decl))
     s << " GLOBAL";