[PATCH] add support for placing variables in shared memory

[Alexander Monakov <amonakov at ispras dot ru>]

Allow using __attribute__((shared)) to place static variables in '.shared'
memory space.

Previously posted here:

[gomp-nvptx 04/13] nvptx backend: add support for placing variables in shared memory
https://gcc.gnu.org/ml/gcc-patches/2016-01/msg01546.html

[gomp-nvptx] doc: document nvptx shared attribute
https://gcc.gnu.org/ml/gcc-patches/2016-04/msg00940.html

2016-04-19  Alexander Monakov  <amonakov@ispras.ru>

	* doc/extend.texi (Nvidia PTX Variable Attributes): New section.

2016-01-17  Alexander Monakov  <amonakov@ispras.ru>

	* config/nvptx/nvptx.c (nvptx_encode_section_info): Handle "shared"
	attribute.
	(nvptx_handle_shared_attribute): New.  Use it...
	(nvptx_attribute_table): ... here (new entry).


diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index 2d4dad1..e9e4d06 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -234,9 +224,12 @@ nvptx_encode_section_info (tree decl, rtx rtl, int first)
       if (TREE_CONSTANT (decl))
 	area = DATA_AREA_CONST;
       else if (TREE_CODE (decl) == VAR_DECL)
-	/* TODO: This would be a good place to check for a .shared or
-	   other section name.  */
-	area = TREE_READONLY (decl) ? DATA_AREA_CONST : DATA_AREA_GLOBAL;
+	{
+	  if (lookup_attribute ("shared", DECL_ATTRIBUTES (decl)))
+	    area = DATA_AREA_SHARED;
+	  else
+	    area = TREE_READONLY (decl) ? DATA_AREA_CONST : DATA_AREA_GLOBAL;
+	}
 
       SET_SYMBOL_DATA_AREA (XEXP (rtl, 0), area);
     }
@@ -3805,12 +4025,36 @@ nvptx_handle_kernel_attribute (tree *node, tree name, tree ARG_UNUSED (args),
   return NULL_TREE;
 }
 
+/* Handle a "shared" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+nvptx_handle_shared_attribute (tree *node, tree name, tree ARG_UNUSED (args),
+			       int ARG_UNUSED (flags), bool *no_add_attrs)
+{
+  tree decl = *node;
+
+  if (TREE_CODE (decl) != VAR_DECL)
+    {
+      error ("%qE attribute only applies to variables", name);
+      *no_add_attrs = true;
+    }
+  else if (current_function_decl && !TREE_STATIC (decl))
+    {
+      error ("%qE attribute only applies to non-stack variables", name);
+      *no_add_attrs = true;
+    }
+
+  return NULL_TREE;
+}
+
 /* Table of valid machine attributes.  */
 static const struct attribute_spec nvptx_attribute_table[] =
 {
   /* { name, min_len, max_len, decl_req, type_req, fn_type_req, handler,
        affects_type_identity } */
   { "kernel", 0, 0, true, false,  false, nvptx_handle_kernel_attribute, false },
+  { "shared", 0, 0, true, false,  false, nvptx_handle_shared_attribute, false },
   { NULL, 0, 0, false, false, false, NULL, false }
 };
 
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index e11ce4d..5eeb179 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -5469,6 +5469,7 @@ attributes.
 * MeP Variable Attributes::
 * Microsoft Windows Variable Attributes::
 * MSP430 Variable Attributes::
+* Nvidia PTX Variable Attributes::
 * PowerPC Variable Attributes::
 * RL78 Variable Attributes::
 * SPU Variable Attributes::
@@ -6099,6 +6100,20 @@ same name (@pxref{MSP430 Function Attributes}).
 These attributes can be applied to both functions and variables.
 @end table
 
+@node Nvidia PTX Variable Attributes
+@subsection Nvidia PTX Variable Attributes
+
+These variable attributes are supported by the Nvidia PTX back end:
+
+@table @code
+@item shared
+@cindex @code{shared} attribute, Nvidia PTX
+Use this attribute to place a variable in the @code{.shared} memory space.
+This memory space is private to each cooperative thread array; only threads
+within one thread block refer to the same instance of the variable.
+The runtime does not initialize variables in this memory space.
+@end table
+
 @node PowerPC Variable Attributes
 @subsection PowerPC Variable Attributes