d: Use weak linkage for template symbols instead of gnu.linkonce (PR99914)

The default linkage of templates in the D language is now DECL_WEAK
instead of  DECL_ONE_ONLY, if supported.  This better matches the
expected override semantics of template symbols compiled to object code.

For example:

 module rt.config;
 template rt_flag()
 {
   pragma(mangle, "rt_flag") __gshared bool rt_flag = true;
 }

 module main;
 extern(C) __gshared bool rt_flag = false;

The above currently does not succeed in linking due to there being
multiple definitions of `rt_flag' in different sections that aren't
considered mergeable.

The compiler flag enabling toggling of this has been given a clearer
named `-fweak-templates', which distinguishes itself from G++ `-fweak',
which is intended only for testing.

gcc/d/ChangeLog:

	PR d/99914
	* d-lang.cc (d_init): Disable flag_weak_templates if no support for
	weak or one-only symbols.
	* d-tree.h (VAR_OR_FUNCTION_DECL_CHECK): New macro.
	(DECL_INSTANTIATED): New macro.
	(d_comdat_linkage): Remove declaration.
	(d_linkonce_linkage): Remove declaration.
	(set_linkage_for_decl): New declaration.
	* decl.cc (DeclVisitor::visit (StructDeclaration *)): Replace call to
	d_linkonce_linkage with setting DECL_INSTANTIATED.
	(DeclVisitor::visit (ClassDeclaration *)): Likewise.
	(DeclVisitor::visit (EnumDeclaration *)): Likewise.
	(DeclVisitor::visit (InterfaceDeclaration *)): Remove call to
	d_linkonce_linkage.
	(get_symbol_decl): Call set_linkage_for_decl instead of
	d_linkonce_linkage.
	(d_finish_decl): Call set_linkage_for_decl.
	(d_comdat_linkage): Made function static.  Only set DECL_COMDAT for
	DECL_INSTANTIATED decls.
	(d_linkonce_linkage): Remove function.
	(d_weak_linkage): New function.
	(set_linkage_for_decl): New function.
	* gdc.texi (Runtime Options): Rename -fno-weak to -fno-weak-templates,
	update documentation of option.
	* lang.opt (fweak): Rename option to ...
	(fweak-templates): ... this.  Update help string.
	* modules.cc (get_internal_fn): Add Prot parameter.  Set generated
	function flag.
	(build_internal_fn): Update call to get_internal_fn.
	(build_dso_cdtor_fn): Likewise.
	(register_moduleinfo): Call d_finish_decl on dso_slot_node and
	dso_initialized_node.
	* typeinfo.cc (TypeInfoVisitor::internal_reference): Call
	set_linkage_for_decl instead of d_comdat_linkage.
	(TypeInfoDeclVisitor::visit (TypeInfoDeclaration *)): Remove calls to
	d_linkonce_linkage and d_comdat_linkage.
	(get_cpp_typeinfo_decl): Likewise.

gcc/testsuite/ChangeLog:

	PR d/99914
	* gdc.dg/pr99914.d: New test.

1 files changed, 8 insertions, 12 deletions

diff --git a/gcc/d/modules.cc b/gcc/d/modules.cc
index af69815..8786344 100644
--- a/gcc/d/modules.cc
+++ b/gcc/d/modules.cc
@@ -125,7 +125,7 @@ static Module *current_module_decl;
    by both module initialization and dso handlers.  */
 
 static FuncDeclaration *
-get_internal_fn (tree ident)
+get_internal_fn (tree ident, const Prot &prot)
 {
   Module *mod = current_module_decl;
   const char *name = IDENTIFIER_POINTER (ident);
@@ -141,9 +141,10 @@ get_internal_fn (tree ident)
 
   FuncDeclaration *fd = FuncDeclaration::genCfunc (NULL, Type::tvoid,
 						   Identifier::idPool (name));
+  fd->generated = true;
   fd->loc = Loc (mod->srcfile->toChars (), 1, 0);
   fd->parent = mod;
-  fd->protection.kind = Prot::private_;
+  fd->protection = prot;
   fd->semanticRun = PASSsemantic3done;
 
   return fd;
@@ -155,7 +156,7 @@ get_internal_fn (tree ident)
 static tree
 build_internal_fn (tree ident, tree expr)
 {
-  FuncDeclaration *fd = get_internal_fn (ident);
+  FuncDeclaration *fd = get_internal_fn (ident, Prot (Prot::private_));
   tree decl = get_symbol_decl (fd);
 
   tree old_context = start_function (fd);
@@ -337,7 +338,8 @@ build_dso_cdtor_fn (bool ctor_p)
 	}
     }
    */
-  FuncDeclaration *fd = get_internal_fn (get_identifier (name));
+  FuncDeclaration *fd = get_internal_fn (get_identifier (name),
+					 Prot (Prot::public_));
   tree decl = get_symbol_decl (fd);
 
   TREE_PUBLIC (decl) = 1;
@@ -345,8 +347,6 @@ build_dso_cdtor_fn (bool ctor_p)
   DECL_VISIBILITY (decl) = VISIBILITY_HIDDEN;
   DECL_VISIBILITY_SPECIFIED (decl) = 1;
 
-  d_comdat_linkage (decl);
-
   /* Start laying out the body.  */
   tree old_context = start_function (fd);
   rest_of_decl_compilation (decl, 1, 0);
@@ -443,15 +443,11 @@ register_moduleinfo (Module *decl, tree minfo)
   /* Declare dso_slot and dso_initialized.  */
   dso_slot_node = build_dso_registry_var (GDC_PREFIX ("dso_slot"),
 					  ptr_type_node);
-  DECL_EXTERNAL (dso_slot_node) = 0;
-  d_comdat_linkage (dso_slot_node);
-  rest_of_decl_compilation (dso_slot_node, 1, 0);
+  d_finish_decl (dso_slot_node);
 
   dso_initialized_node = build_dso_registry_var (GDC_PREFIX ("dso_initialized"),
 						 boolean_type_node);
-  DECL_EXTERNAL (dso_initialized_node) = 0;
-  d_comdat_linkage (dso_initialized_node);
-  rest_of_decl_compilation (dso_initialized_node, 1, 0);
+  d_finish_decl (dso_initialized_node);
 
   /* Declare dso_ctor() and dso_dtor().  */
   tree dso_ctor = build_dso_cdtor_fn (true);