d: Add `@register' attribute to compiler and library.

The `@register` attribute specifies that a local or `__gshared` variable
is to be given a register storage-class in the C sense of the term, and
will be placed into a register named `registerName`.

The variable needs to boiled down to a data type that fits the target
register.  It also cannot have either thread-local or `extern` storage.
It is an error to take the address of a register variable.

	PR d/105413

gcc/d/ChangeLog:

	* d-attribs.cc (d_handle_register_attribute): New function.
	(d_langhook_attribute_table): Add register attribute.
	* d-codegen.cc (d_mark_addressable): Error if taken address of
	register variable.
	(build_frame_type): Error if register variable has non-local
	references.
	* d-tree.h (d_mark_addressable): Add complain parameter.
	* decl.cc (get_symbol_decl): Mark register varibles DECL_REGISTER.
	Error when register variable declared thread-local or extern.
	* expr.cc (ExprVisitor::visit (IndexExp *)): Don't complain about
	marking register vectors as addressable in an ARRAY_REF.

libphobos/ChangeLog:

	* libdruntime/gcc/attributes.d (register): Define.

gcc/testsuite/ChangeLog:

	* gdc.dg/attr_register1.d: New test.
	* gdc.dg/attr_register2.d: New test.
	* gdc.dg/attr_register3.d: New test.

1 files changed, 22 insertions, 2 deletions

diff --git a/gcc/d/decl.cc b/gcc/d/decl.cc
index b82e2d5..5032ae0 100644
--- a/gcc/d/decl.cc
+++ b/gcc/d/decl.cc
@@ -670,10 +670,14 @@ public:
 	    rest_of_decl_compilation (decl, 1, 0);
 	  }
       }
-    else if (d->isDataseg () && !(d->storage_class & STCextern))
+    else if (d->isDataseg ())
       {
 	tree decl = get_symbol_decl (d);
 
+	/* Only need to build the VAR_DECL for extern declarations.  */
+	if (d->storage_class & STCextern)
+	  return;
+
 	/* Duplicated VarDeclarations map to the same symbol.  Check if this
 	   is the one declaration which will be emitted.  */
 	tree ident = DECL_ASSEMBLER_NAME (decl);
@@ -1343,7 +1347,11 @@ get_symbol_decl (Declaration *decl)
   if (decl->storage_class & STCvolatile)
     TREE_THIS_VOLATILE (decl->csym) = 1;
 
-  /* Likewise, so could the deprecated attribute.  */
+  /* Symbol was marked register.  */
+  if (decl->storage_class & STCregister)
+    DECL_REGISTER (decl->csym) = 1;
+
+  /* Symbol was declared with deprecated attribute.  */
   if (decl->storage_class & STCdeprecated)
     TREE_DEPRECATED (decl->csym) = 1;
 
@@ -1376,6 +1384,18 @@ get_symbol_decl (Declaration *decl)
   /* Apply any user attributes that may affect semantic meaning.  */
   apply_user_attributes (decl, decl->csym);
 
+  /* Handle any conflicts between D language attributes and compiler-recognized
+   * user attributes.  */
+  if (VAR_P (decl->csym) && DECL_HARD_REGISTER (decl->csym))
+    {
+      if (decl->storage_class & STCextern)
+	error_at (make_location_t (decl->loc), "explicit register variable "
+		  "%qs declared %<extern%>", decl->toChars ());
+      else if (decl->isThreadlocal ())
+	error_at (make_location_t (decl->loc), "explicit register variable "
+		  "%qs declared thread local", decl->toChars ());
+    }
+
   /* %% Probably should be a little more intelligent about setting this.  */
   TREE_USED (decl->csym) = 1;
   d_keep (decl->csym);