cygming.h (SUBTARGET_ATTRIBUTE_TABLE): Define, with entry for selectany attribute.

* config/i386/cygming.h (SUBTARGET_ATTRIBUTE_TABLE): Define,
	with entry for selectany attribute.
	* config/i386/i386-protos.h (ix86_handle_selectany_attribute):
	Declare.
	* config/i386/winnt.c (ix86_handle_selectany_attribute): Define.
	(i386_pe_asm_named_section): Handle sections generated by
	selectany attribute.
	* doc/extend.texi (selectany): Document attribute.

From-SVN: r97377

gcc/ChangeLog

@@ -1,3 +1,14 @@
+2005-04-01  Danny Smith  <dannysmith@users.sourceforge.net>
+
+	* config/i386/cygming.h (SUBTARGET_ATTRIBUTE_TABLE): Define,
+	with entry for selectany attribute.
+	* config/i386/i386-protos.h (ix86_handle_selectany_attribute):
+	Declare.
+	* config/i386/winnt.c (ix86_handle_selectany_attribute): Define.
+	(i386_pe_asm_named_section): Handle sections generated by
+	selectany attribute.
+	* doc/extend.texi (selectany): Document attribute.
+
 2005-04-01  Paolo Bonzini  <bonzini@gnu.org>
 	    Jan Hubicka  <jh@suse.cz>
 

gcc/config/i386/cygming.h

@@ -418,6 +418,10 @@ extern int i386_pe_dllimport_name_p (const char *);
 #undef TARGET_USE_LOCAL_THUNK_ALIAS_P
 #define TARGET_USE_LOCAL_THUNK_ALIAS_P(DECL) (!DECL_ONE_ONLY (DECL))
 
+#define SUBTARGET_ATTRIBUTE_TABLE \
+  /* { name, min_len, max_len, decl_req, type_req, fn_type_req, handler } */ \
+  { "selectany", 0, 0, true, false, false, ix86_handle_selectany_attribute }
+
 #undef TREE
 
 #ifndef BUFSIZ

gcc/config/i386/i386-protos.h

@@ -216,6 +216,7 @@ extern int ix86_data_alignment (tree, int);
 extern int ix86_local_alignment (tree, int);
 extern int ix86_constant_alignment (tree, int);
 extern tree ix86_handle_shared_attribute (tree *, tree, tree, int, bool *);
+extern tree ix86_handle_selectany_attribute (tree *, tree, tree, int, bool *); 
 
 extern unsigned int i386_pe_section_type_flags (tree, const char *, int);
 extern void i386_pe_asm_named_section (const char *, unsigned int, tree);

gcc/config/i386/winnt.c

@@ -78,6 +78,36 @@ ix86_handle_shared_attribute (tree *node, tree name,
 
   return NULL_TREE;
 }
+
+/* Handle a "selectany" attribute;
+   arguments as in struct attribute_spec.handler.  */
+tree
+ix86_handle_selectany_attribute (tree *node, tree name,
+			         tree args ATTRIBUTE_UNUSED,
+			         int flags ATTRIBUTE_UNUSED,
+				 bool *no_add_attrs)
+{
+  /* The attribute applies only to objects that are initialized and have
+     external linkage,  */	
+  if (TREE_CODE (*node) == VAR_DECL && TREE_PUBLIC (*node)
+      && (DECL_INITIAL (*node)
+          /* If an object is initialized with a ctor, the static
+	     initialization and destruction code for it is present in
+	     each unit defining the object.  The code that calls the
+	     ctor is protected by a link-once guard variable, so that
+	     the object still has link-once semantics,  */
+    	  || TYPE_NEEDS_CONSTRUCTING (TREE_TYPE (*node))))
+    make_decl_one_only (*node);
+  else
+    {	
+      error ("%qs attribute applies only to initialized variables"
+       	     " with external linkage",  IDENTIFIER_POINTER (name));
+      *no_add_attrs = true;
+    }
+
+  return NULL_TREE;
+}
+
 
 /* Return the type that we should use to determine if DECL is
    imported or exported.  */
@@ -622,7 +652,7 @@ i386_pe_section_type_flags (tree decl, const char *name, int reloc)
 
 void
 i386_pe_asm_named_section (const char *name, unsigned int flags, 
-			   tree decl ATTRIBUTE_UNUSED)
+			   tree decl)
 {
   char flagchars[8], *f = flagchars;
 
@@ -649,10 +679,16 @@ i386_pe_asm_named_section (const char *name, unsigned int flags,
   if (flags & SECTION_LINKONCE)
     {
       /* Functions may have been compiled at various levels of
-         optimization so we can't use `same_size' here.
-         Instead, have the linker pick one.  */
+	 optimization so we can't use `same_size' here.
+	 Instead, have the linker pick one, without warning.
+	 If 'selectany' attibute has been specified,  MS compiler
+	 sets 'discard' characteristic, rather than telling linker
+	 to warn of size or content mismatch, so do the same.  */ 
+      bool discard = (flags & SECTION_CODE)
+		      || lookup_attribute ("selectany",
+					   DECL_ATTRIBUTES (decl));	 
       fprintf (asm_out_file, "\t.linkonce %s\n",
-	       (flags & SECTION_CODE ? "discard" : "same_size"));
+	       (discard  ? "discard" : "same_size"));
     }
 }
 

gcc/doc/extend.texi

@@ -3000,6 +3000,26 @@ struct S  __attribute__ ((vector_size (16))) foo;
 is invalid even if the size of the structure is the same as the size of
 the @code{int}.
 
+@item selectany
+The @code{selectany} attribute causes an initialized global variable to
+have link-once semantics.  When multiple definitions of the variable are
+encountered by the linker, the first is selected and the remainder are
+discarded.  Following usage by the Microsoft compiler, the linker is told
+@emph{not} to warn about size or content differences of the multiple
+definitions.
+
+Although the primary usage of this attribute is for POD types, the
+attribute can also be applied to global C++ objects that are initialized
+by a constructor.  In this case, the static initialization and destruction
+code for the object is emitted in each translation defining the object,
+but the calls to the constructor and destructor are protected by a
+link-once guard variable. 
+
+The @code{selectany} attribute is only available on Microsoft Windows
+targets.  You can use @code{__declspec (selectany)} as a synonym for
+@code{__attribute__ ((selectany))} for compatibility with other
+compilers.
+
 @item weak
 The @code{weak} attribute is described in @xref{Function Attributes}.