decl.c: Do not emit a variable for a object that has an address representation clause...

2008-05-20  Tristan Gingold  <gingold@adacore.com>

	* decl.c: Do not emit a variable for a object that has an address
	representation clause whose value is known at compile time.
	When a variable has an address clause whose value is known at compile
	time, refer to this variable by using directly the address instead of
	dereferencing a pointer.

From-SVN: r135618

gcc/ada/decl.c

@@ -122,6 +122,17 @@ static void check_ok_for_atomic (tree, Entity_Id, bool);
 static int compatible_signatures_p (tree ftype1, tree ftype2);
 static void rest_of_type_decl_compilation_no_defer (tree);
 
+/* Return true if GNAT_ADDRESS is a compile time known value.
+   In particular catch System'To_Address.  */
+
+static bool
+compile_time_known_address_p (Node_Id gnat_address)
+{
+  return ((Nkind (gnat_address) == N_Unchecked_Type_Conversion
+	   && Compile_Time_Known_Value (Expression (gnat_address)))
+	  || Compile_Time_Known_Value (gnat_address));
+}
+
 /* Given GNAT_ENTITY, an entity in the incoming GNAT tree, return a
    GCC type corresponding to that entity.  GNAT_ENTITY is assumed to
    refer to an Ada type.  */
@@ -1026,7 +1037,9 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 	      = build_reference_type_for_mode (gnu_type, ptr_mode, true);
 	    gnu_address = convert (gnu_type, gnu_address);
 	    used_by_ref = true;
-	    const_flag = !Is_Public (gnat_entity);
+	    const_flag = !Is_Public (gnat_entity)
+	      || compile_time_known_address_p (Expression (Address_Clause
+							   (gnat_entity)));
 
 	    /* If we don't have an initializing expression for the underlying
 	       variable, the initializing expression for the pointer is the
@@ -1058,9 +1071,24 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 	      = build_reference_type_for_mode (gnu_type, ptr_mode, true);
 	    gnu_size = NULL_TREE;
 
-	    gnu_expr = NULL_TREE;
 	    /* No point in taking the address of an initializing expression
 	       that isn't going to be used.  */
+	    gnu_expr = NULL_TREE;
+
+	    /* If it has an address clause whose value is known at compile
+	       time, make the object a CONST_DECL.  This will avoid a
+	       useless dereference.  */
+	    if (Present (Address_Clause (gnat_entity)))
+	      {
+		Node_Id gnat_address
+		  = Expression (Address_Clause (gnat_entity));
+
+		if (compile_time_known_address_p (gnat_address))
+		  {
+		    gnu_expr = gnat_to_gnu (gnat_address);
+		    const_flag = true;
+		  }
+	      }
 
 	    used_by_ref = true;
 	  }
@@ -1258,7 +1286,8 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 	   for these.  */
 	if (TREE_CODE (gnu_decl) == CONST_DECL
 	    && (definition || Sloc (gnat_entity) > Standard_Location)
-	    && (Is_Public (gnat_entity)
+	    && ((Is_Public (gnat_entity)
+		 && !Present (Address_Clause (gnat_entity)))
 		|| optimize == 0
 		|| Address_Taken (gnat_entity)
 		|| Is_Aliased (gnat_entity)
@@ -1271,6 +1300,10 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 				      gnat_entity);
 
 	    SET_DECL_CONST_CORRESPONDING_VAR (gnu_decl, gnu_corr_var);
+
+	    /* As debugging information will be generated for the variable,
+	       do not generate information for the constant.  */
+	    DECL_IGNORED_P (gnu_decl) = true;
 	  }
 
 	/* If this is declared in a block that contains a block with an