[Bug lto/54312] New: uniquify_nodes takes 12% of Mozilla LTO build

["hubicka at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54312

             Bug #: 54312
           Summary: uniquify_nodes takes 12% of Mozilla LTO build
    Classification: Unclassified
           Product: gcc
           Version: lto
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hubicka@gcc.gnu.org


uniquify_nodes has quadratic loop removing types from variant lists:
          /* Remove us from our main variant list if we are not the
             variant leader.  */
          if (TYPE_MAIN_VARIANT (t) != t)
            {
              tem = TYPE_MAIN_VARIANT (t);
              while (tem && TYPE_NEXT_VARIANT (tem) != t)
                tem = TYPE_NEXT_VARIANT (tem);
              if (tem)
                TYPE_NEXT_VARIANT (tem) = TYPE_NEXT_VARIANT (t);
              TYPE_NEXT_VARIANT (t) = NULL_TREE;
            }
this consume a lot of time building Mozilla (and was introduced by Michael's
patch cleaning up the stream in process). Can't we do a bit better here?

(this was introduced in 4.7)

Honza