function Original_Node (Node : Node_Id) return Node_Id;
pragma Inline (Original_Node);
-- If Node has not been rewritten, then returns its input argument
- -- unchanged, else returns the Node for the original subtree.
+ -- unchanged, else returns the Node for the original subtree. Note that
+ -- this is used extensively by ASIS on the trees constructed in ASIS mode
+ -- to reconstruct the original semantic tree. See section in sinfo.ads
+ -- for requirements on original nodes returned by this function.
--
-- Note: Parents are not preserved in original tree nodes that are
-- retrieved in this way (i.e. their children may have children whose
- -- pointers which reference some other node).
-
+ -- pointers which reference some other node). This needs more details???
+ --
-- Note: there is no direct mechanism for deleting an original node (in
-- a manner that can be reversed later). One possible approach is to use
-- Rewrite to substitute a null statement for the node to be deleted.
-- code is being generated, since they involved expander actions that
-- destroy the tree.
+ ---------------
+ -- ASIS Mode --
+ ---------------
+
+ -- When a file is compiled in ASIS mode (-gnatct), expansion is skipped,
+ -- and the analysis must generate a tree in a form that meets all ASIS
+ -- requirements.
+
+ -- ASIS must be able to recover the original tree that corresponds to the
+ -- source. It relies heavily on Original_Node for this purpose, which as
+ -- described in Atree, records the history when a node is rewritten. ASIS
+ -- uses Original_Node to recover the original node before the Rewrite.
+
+ -- At least in ASIS mode (not really important in non-ASIS mode), when
+ -- N1 is rewritten as N2:
+
+ -- The subtree rooted by the original node N1 should be fully decorated,
+ -- i.e. all semantic fields noted in sinfo.ads should be set properly
+ -- and any referenced entities should be complete (with exceptions for
+ -- representation information, noted below).
+
+ -- For all the direct descendants of N1 (original node) their Parent
+ -- links should point not to N1, but to N2 (rewriting node).
+
+ -- The Parent links of rewritten nodes (N1 in this example) are set in
+ -- some cases (to point to the rewritten parent), but in other cases
+ -- they are set to Empty. This needs sorting out ??? It would be much
+ -- cleaner if they could always be set in the original node ???
+
+ -- Representation Information
+
+ -- For the purposes of the data description annex, the representation
+ -- information for source declared entities must be complete in the
+ -- ASIS tree.
+
+ -- This requires that the front end call the back end (gigi/gcc) in
+ -- a special "back annotate only" mode to obtain information on layout
+ -- from the back end.
+
+ -- For the purposes of this special "back annotate only" mode, the
+ -- requirements that would normally need to be met to generate code
+ -- are relaxed as follows:
+
+ -- Anonymous types need not have full representation information (e.g.
+ -- sizes need not be set for types where the front end would normally
+ -- set the sizes), since anonymous types can be ignored in this mode.
+
+ -- In this mode, gigi will see at least fragments of a fully annotated
+ -- unexpanded tree. This means that it will encounter nodes it does
+ -- not normally handle (such as stubs, task bodies etc). It should
+ -- simply ignore these nodes, since they are not relevant to the task
+ -- of back annotating representation information.
+
------------------------
-- Common Flag Fields --
------------------------
projects / platform / upstream / gcc.git / commitdiff