[PATCH 8/8] nvptx: handle OpenMP "omp target entrypoint"

[Alexander Monakov]

This patch implements emission of OpenMP target region entrypoints: the
compiler emits the target function with '$impl' appended to the name, and
under the original name it emits a short entry sequence that sets up shared
memory arrays and calls the target function via 'gomp_nvptx_main' (which is
implemented in libgomp).

	* config/nvptx/nvptx.c (write_as_kernel): Restrict to OpenACC target
	regions.
	(write_omp_entry): New.  Use it...
	(nvptx_declare_function_name): ...here to emit OpenMP target region
	entrypoints.
	(nvptx_record_offload_symbol): Handle NULL attributes.
---
 gcc/config/nvptx/nvptx.c | 82 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 78 insertions(+), 4 deletions(-)

diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index d959f85..5e47002 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -723,7 +723,10 @@ static bool
 write_as_kernel (tree attrs)
 {
   return (lookup_attribute ("kernel", attrs) != NULL_TREE
-	  || lookup_attribute ("omp target entrypoint", attrs) != NULL_TREE);
+	  || (lookup_attribute ("omp target entrypoint", attrs) != NULL_TREE
+	      && lookup_attribute ("oacc function", attrs) != NULL_TREE));
+  /* For OpenMP target regions, the corresponding kernel entry is emitted from
+     write_omp_entry as a separate function.  */
 }
 
 /* Emit a linker marker for a function decl or defn.  */
@@ -1073,6 +1076,69 @@ nvptx_init_unisimt_predicate (FILE *file)
   need_unisimt_decl = true;
 }
 
+/* Emit kernel NAME for function ORIG outlined for an OpenMP 'target' region:
+
+   extern void gomp_nvptx_main (void (*fn)(void*), void *fnarg);
+   void __attribute__((kernel)) NAME (void *arg, char *stack, size_t stacksize)
+   {
+     __nvptx_stacks[tid.y] = stack + stacksize * (ctaid.x * ntid.y + tid.y + 1);
+     __nvptx_uni[tid.y] = 0;
+     gomp_nvptx_main (ORIG, arg);
+   }
+   ORIG itself should not be emitted as a PTX .entry function.  */
+
+static void
+write_omp_entry (FILE *file, const char *name, const char *orig)
+{
+  static bool gomp_nvptx_main_declared;
+  if (!gomp_nvptx_main_declared)
+    {
+      gomp_nvptx_main_declared = true;
+      write_fn_marker (func_decls, false, true, "gomp_nvptx_main");
+      func_decls << ".extern .func gomp_nvptx_main (.param.u" << POINTER_SIZE
+        << " %in_ar1, .param.u" << POINTER_SIZE << " %in_ar2);\n";
+    }
+#define ENTRY_TEMPLATE(PS, PS_BYTES, MAD_PS_32) "\
+ (.param.u" PS " %arg, .param.u" PS " %stack, .param.u" PS " %sz)\n\
+{\n\
+	.reg.u32 %r<3>;\n\
+	.reg.u" PS " %R<4>;\n\
+	mov.u32 %r0, %tid.y;\n\
+	mov.u32 %r1, %ntid.y;\n\
+	mov.u32 %r2, %ctaid.x;\n\
+	cvt.u" PS ".u32 %R1, %r0;\n\
+	" MAD_PS_32 " %R1, %r1, %r2, %R1;\n\
+	mov.u" PS " %R0, __nvptx_stacks;\n\
+	" MAD_PS_32 " %R0, %r0, " PS_BYTES ", %R0;\n\
+	ld.param.u" PS " %R2, [%stack];\n\
+	ld.param.u" PS " %R3, [%sz];\n\
+	add.u" PS " %R2, %R2, %R3;\n\
+	mad.lo.u" PS " %R2, %R1, %R3, %R2;\n\
+	st.shared.u" PS " [%R0], %R2;\n\
+	mov.u" PS " %R0, __nvptx_uni;\n\
+	" MAD_PS_32 " %R0, %r0, 4, %R0;\n\
+	mov.u32 %r0, 0;\n\
+	st.shared.u32 [%R0], %r0;\n\
+	mov.u" PS " %R0, \0;\n\
+	ld.param.u" PS " %R1, [%arg];\n\
+	{\n\
+		.param.u" PS " %P<2>;\n\
+		st.param.u" PS " [%P0], %R0;\n\
+		st.param.u" PS " [%P1], %R1;\n\
+		call.uni gomp_nvptx_main, (%P0, %P1);\n\
+	}\n\
+	ret.uni;\n\
+}\n"
+  static const char entry64[] = ENTRY_TEMPLATE ("64", "8", "mad.wide.u32");
+  static const char entry32[] = ENTRY_TEMPLATE ("32", "4", "mad.lo.u32  ");
+#undef ENTRY_TEMPLATE
+  const char *entry_1 = TARGET_ABI64 ? entry64 : entry32;
+  /* Position ENTRY_2 after the embedded nul using strlen of the prefix.  */
+  const char *entry_2 = entry_1 + strlen (entry64) + 1;
+  fprintf (file, ".visible .entry %s%s%s%s", name, entry_1, orig, entry_2);
+  need_softstack_decl = need_unisimt_decl = true;
+}
+
 /* Implement ASM_DECLARE_FUNCTION_NAME.  Writes the start of a ptx
    function, including local var decls and copies from the arguments to
    local regs.  */
@@ -1084,6 +1150,14 @@ nvptx_declare_function_name (FILE *file, const char *name, const_tree decl)
   tree result_type = TREE_TYPE (fntype);
   int argno = 0;
 
+  if (lookup_attribute ("omp target entrypoint", DECL_ATTRIBUTES (decl))
+      && !lookup_attribute ("oacc function", DECL_ATTRIBUTES (decl)))
+    {
+      char *buf = (char *) alloca (strlen (name) + sizeof ("$impl"));
+      sprintf (buf, "%s$impl", name);
+      write_omp_entry (file, name, buf);
+      name = buf;
+    }
   /* We construct the initial part of the function into a string
      stream, in order to share the prototype writing code.  */
   std::stringstream s;
@@ -4153,13 +4227,13 @@ nvptx_record_offload_symbol (tree decl)
     case FUNCTION_DECL:
       {
 	tree attr = get_oacc_fn_attrib (decl);
-	tree dims = TREE_VALUE (attr);
-	unsigned ix;
+	/* OpenMP offloading does not set this attribute.  */
+	tree dims = attr ? TREE_VALUE (attr) : NULL_TREE;
 
 	fprintf (asm_out_file, "//:FUNC_MAP \"%s\"",
 		 IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl)));
 
-	for (ix = 0; ix != GOMP_DIM_MAX; ix++, dims = TREE_CHAIN (dims))
+	for (; dims; dims = TREE_CHAIN (dims))
 	  {
 	    int size = TREE_INT_CST_LOW (TREE_VALUE (dims));
 
-- 
2.6.6