Reverted commit 143546 related to PR c++/26693

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@143562 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 62 insertions, 1 deletions

diff --git a/gcc/c-decl.c b/gcc/c-decl.c
index 8b444d4177a..7f7f2b00ac7 100644
--- a/gcc/c-decl.c
+++ b/gcc/c-decl.c
@@ -1971,6 +1971,67 @@ warn_if_shadowing (tree new_decl)
       }
 }
 
+
+/* Subroutine of pushdecl.
+
+   X is a TYPE_DECL for a typedef statement.  Create a brand new
+   ..._TYPE node (which will be just a variant of the existing
+   ..._TYPE node with identical properties) and then install X
+   as the TYPE_NAME of this brand new (duplicate) ..._TYPE node.
+
+   The whole point here is to end up with a situation where each
+   and every ..._TYPE node the compiler creates will be uniquely
+   associated with AT MOST one node representing a typedef name.
+   This way, even though the compiler substitutes corresponding
+   ..._TYPE nodes for TYPE_DECL (i.e. "typedef name") nodes very
+   early on, later parts of the compiler can always do the reverse
+   translation and get back the corresponding typedef name.  For
+   example, given:
+
+	typedef struct S MY_TYPE;
+	MY_TYPE object;
+
+   Later parts of the compiler might only know that `object' was of
+   type `struct S' if it were not for code just below.  With this
+   code however, later parts of the compiler see something like:
+
+	struct S' == struct S
+	typedef struct S' MY_TYPE;
+	struct S' object;
+
+    And they can then deduce (from the node for type struct S') that
+    the original object declaration was:
+
+		MY_TYPE object;
+
+    Being able to do this is important for proper support of protoize,
+    and also for generating precise symbolic debugging information
+    which takes full account of the programmer's (typedef) vocabulary.
+
+    Obviously, we don't want to generate a duplicate ..._TYPE node if
+    the TYPE_DECL node that we are now processing really represents a
+    standard built-in type.  */
+
+static void
+clone_underlying_type (tree x)
+{
+  if (DECL_IS_BUILTIN (x))
+    {
+      if (TYPE_NAME (TREE_TYPE (x)) == 0)
+	TYPE_NAME (TREE_TYPE (x)) = x;
+    }
+  else if (TREE_TYPE (x) != error_mark_node
+	   && DECL_ORIGINAL_TYPE (x) == NULL_TREE)
+    {
+      tree tt = TREE_TYPE (x);
+      DECL_ORIGINAL_TYPE (x) = tt;
+      tt = build_variant_type_copy (tt);
+      TYPE_NAME (tt) = x;
+      TREE_USED (tt) = TREE_USED (x);
+      TREE_TYPE (x) = tt;
+    }
+}
+
 /* Record a decl-node X as belonging to the current lexical scope.
    Check for errors (such as an incompatible declaration for the same
    name already seen in the same scope).
@@ -2193,7 +2254,7 @@ pushdecl (tree x)
 
  skip_external_and_shadow_checks:
   if (TREE_CODE (x) == TYPE_DECL)
-    set_underlying_type (x);
+    clone_underlying_type (x);
 
   bind (name, x, scope, /*invisible=*/false, nested);