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[PATCH][?/n] LTO type merging cleanup


We can end up with an infinite recursion as gimple_register_type
tries to register TYPE_MAIN_VARIANT first.  This is because we
are being called from the LTO type-fixup code which walks the
type graph and adjusts types to their leaders.  So we can
be called for type SCCs that are only partially fixed up yet
which means TYPE_MAIN_VARIANT might temporarily not honor
the invariant that the main variant of a main variant is itself.
Thus, simply avoid recursing more than once - we are sure that
we will be reaching at most type duplicates in further recursion.

Bootstrap & regtest pending on x86_64-unknown-linux-gnu.

Richard.

2011-05-18  Richard Guenther  <rguenther@suse.de>

	* gimple.c (gimple_register_type_1): New function, split out from ...
	(gimple_register_type): ... here.  Avoid infinite recursion.

Index: gcc/gimple.c
===================================================================
--- gcc/gimple.c	(revision 173852)
+++ gcc/gimple.c	(working copy)
@@ -4487,23 +4509,17 @@ gimple_type_eq (const void *p1, const vo
 }
 
 
-/* Register type T in the global type table gimple_types.
-   If another type T', compatible with T, already existed in
-   gimple_types then return T', otherwise return T.  This is used by
-   LTO to merge identical types read from different TUs.  */
+/* Worker for gimple_register_type.
+   Register type T in the global type table gimple_types.
+   When REGISTERING_MV is false first recurse for the main variant of T.  */
 
-tree
-gimple_register_type (tree t)
+static tree
+gimple_register_type_1 (tree t, bool registering_mv)
 {
   void **slot;
   gimple_type_leader_entry *leader;
   tree mv_leader = NULL_TREE;
 
-  gcc_assert (TYPE_P (t));
-
-  if (!gimple_type_leader)
-    gimple_type_leader = ggc_alloc_cleared_vec_gimple_type_leader_entry_s
-				(GIMPLE_TYPE_LEADER_SIZE);
   /* If we registered this type before return the cached result.  */
   leader = &gimple_type_leader[TYPE_UID (t) % GIMPLE_TYPE_LEADER_SIZE];
   if (leader->type == t)
@@ -4511,12 +4527,14 @@ gimple_register_type (tree t)
 
   /* Always register the main variant first.  This is important so we
      pick up the non-typedef variants as canonical, otherwise we'll end
-     up taking typedef ids for structure tags during comparison.  */
-  if (TYPE_MAIN_VARIANT (t) != t)
-    mv_leader = gimple_register_type (TYPE_MAIN_VARIANT (t));
-
-  if (gimple_types == NULL)
-    gimple_types = htab_create_ggc (16381, gimple_type_hash, gimple_type_eq, 0);
+     up taking typedef ids for structure tags during comparison.
+     It also makes sure that main variants will be merged to main variants.
+     As we are operating on a possibly partially fixed up type graph
+     do not bother to recurse more than once, otherwise we may end up
+     walking in circles.  */
+  if (!registering_mv
+      && TYPE_MAIN_VARIANT (t) != t)
+    mv_leader = gimple_register_type_1 (TYPE_MAIN_VARIANT (t), true);
 
   slot = htab_find_slot (gimple_types, t, INSERT);
   if (*slot
@@ -4602,6 +4620,25 @@ gimple_register_type (tree t)
   return t;
 }
 
+/* Register type T in the global type table gimple_types.
+   If another type T', compatible with T, already existed in
+   gimple_types then return T', otherwise return T.  This is used by
+   LTO to merge identical types read from different TUs.  */
+
+tree
+gimple_register_type (tree t)
+{
+  gcc_assert (TYPE_P (t));
+
+  if (!gimple_type_leader)
+    gimple_type_leader = ggc_alloc_cleared_vec_gimple_type_leader_entry_s
+				(GIMPLE_TYPE_LEADER_SIZE);
+
+  if (gimple_types == NULL)
+    gimple_types = htab_create_ggc (16381, gimple_type_hash, gimple_type_eq, 0);
+
+  return gimple_register_type_1 (t, false);
+}
 
 /* The TYPE_CANONICAL merging machinery.  It should closely resemble
    the middle-end types_compatible_p function.  It needs to avoid


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