Fix PR49078

Index: gcc/gimple.c
===================================================================
--- gcc/gimple.c	(revision 174106)
+++ gcc/gimple.c	(working copy)
@@ -4779,7 +4802,12 @@  gimple_canonical_type_eq (const void *p1
 /* 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.  */
+   LTO to merge identical types read from different TUs.
+
+   ???  This merging does not exactly match how the tree.c middle-end
+   functions will assign TYPE_CANONICAL when new types are created
+   during optimization (which at least happens for pointer and array
+   types).  */
 
 tree
 gimple_register_canonical_type (tree t)
@@ -4800,25 +4828,6 @@  gimple_register_canonical_type (tree t)
   if (TYPE_CANONICAL (t))
     return TYPE_CANONICAL (t);
 
-  /* For pointer and reference types do as the middle-end does - the
-     canonical type is a pointer to the canonical pointed-to type.  */
-  if (TREE_CODE (t) == POINTER_TYPE)
-    {
-      TYPE_CANONICAL (t)
-	  = build_pointer_type_for_mode
-	  (gimple_register_canonical_type (TREE_TYPE (t)),
-	   TYPE_MODE (t), TYPE_REF_CAN_ALIAS_ALL (t));
-      return TYPE_CANONICAL (t);
-    }
-  else if (TREE_CODE (t) == REFERENCE_TYPE)
-    {
-      TYPE_CANONICAL (t)
-	  = build_reference_type_for_mode
-	  (gimple_register_canonical_type (TREE_TYPE (t)),
-	   TYPE_MODE (t), TYPE_REF_CAN_ALIAS_ALL (t));
-      return TYPE_CANONICAL (t);
-    }
-
   if (gimple_canonical_types == NULL)
     gimple_canonical_types = htab_create_ggc (16381, gimple_canonical_type_hash,
 					      gimple_canonical_type_eq, 0);
Index: gcc/alias.c
===================================================================
--- gcc/alias.c	(revision 174106)
+++ gcc/alias.c	(working copy)
@@ -709,10 +709,8 @@  get_alias_set (tree t)
 
   t = TYPE_CANONICAL (t);
 
-  /* Canonical types shouldn't form a tree nor should the canonical
-     type require structural equality checks.  */
-  gcc_checking_assert (TYPE_CANONICAL (t) == t
-		       && !TYPE_STRUCTURAL_EQUALITY_P (t));
+  /* The canonical type should not require structural equality checks.  */
+  gcc_checking_assert (!TYPE_STRUCTURAL_EQUALITY_P (t));
 
   /* If this is a type with a known alias set, return it.  */
   if (TYPE_ALIAS_SET_KNOWN_P (t))
@@ -813,11 +811,19 @@  get_alias_set (tree t)
      That's simple and avoids all the above problems.  */
   else if (POINTER_TYPE_P (t)
 	   && t != ptr_type_node)
-    return get_alias_set (ptr_type_node);
+    set = get_alias_set (ptr_type_node);
 
   /* Otherwise make a new alias set for this type.  */
   else
-    set = new_alias_set ();
+    {
+      /* Each canonical type gets its own alias set, so canonical types
+	 shouldn't form a tree.  It doesn't really matter for types
+	 we handle specially above, so only check it where it possibly
+	 would result in a bogus alias set.  */
+      gcc_checking_assert (TYPE_CANONICAL (t) == t);
+
+      set = new_alias_set ();
+    }
 
   TYPE_ALIAS_SET (t) = set;