[Bug lto/51635] [4.7 regression] ICE in in dwarf2out_finish, at dwarf2out.c:22494 when building Firefox's libxul

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51635

--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-12-21 09:29:05 UTC ---
(In reply to comment #8)
> (In reply to comment #7)
> > On Tue, 20 Dec 2011, Richard Guenther wrote:
> > > > This one is extremely slow. lto1 has already used 12min of CPU time when
> > > > linking libxul and is still running... (3min is normal)
> > > 
> > > That's odd - TREE_TYPE (f1) should already be registered - but I suppose
> > > that adjusting TYPE_NAME might break all the caching we do with the
> > > type-pair cache as TREE_TYPE (TYPE_NAME (f1)) is in the SCC of the
> > > type we change that SCC by that adjustment - probably causing
> > > the hit rate of the type-pair compare cache to become absymal?
> > > Maybe you can check that theory (I have no other idea why the above
> > > should be slow).
> > 
> > Though we should be hitting the gimple_type_leader cache only ...
> > maybe it's too small though?
> 
> Increasing the cache 4-fold doesn't help. 
> I will look deeper tomorrow. In the meantime here is a disassembly of the
> hot-spot.
> 
> uniquify_nodes:
>          :          /* Second fixup all trees in the new cache entries.  */
>          :          for (i = len; i-- > from;)
>     0.00 :          49969f:       mov    %ebp,%eax
>     0.00 :          4996a1:       jmpq   4994b0 <lto_read_decls+0x110>
>     0.00 :          4996a6:       nopw   %cs:0x0(%rax,%rax,1)
>          :              tree t = VEC_index (tree, cache->nodes, i);
>          :              if (t == NULL_TREE)
>          :                continue;
>          :
>          :              if (TREE_CODE (t) == VAR_DECL)
>          :                lto_register_var_decl_in_symtab (data_in, t);
>     0.00 :          4996b0:       mov    0x38(%rsp),%rdi
>     0.00 :          4996b5:       callq  499250
> <lto_register_var_decl_in_symtab>
>     0.00 :          4996ba:       jmpq   499520 <lto_read_decls+0x180>
>          :                     variant list state before fixup is broken.  */
>          :                  tree tem, mv;
>          :
>          :                  /* Remove us from our main variant list if we are
> not the
>          :                     variant leader.  */
>          :                  if (TYPE_MAIN_VARIANT (t) != t)
>     0.00 :          4996bf:       mov    0x68(%r15),%rdi
>     0.00 :          4996c3:       cmp    %rdi,%r15
>     0.00 :          4996c6:       je     499701 <lto_read_decls+0x361>
>          :                    {
>          :                      tem = TYPE_MAIN_VARIANT (t);
>          :                      while (tem && TYPE_NEXT_VARIANT (tem) != t)
>     0.00 :          4996c8:       test   %rdi,%rdi
>     0.00 :          4996cb:       je     4996f9 <lto_read_decls+0x359>
>     0.00 :          4996cd:       mov    0x60(%rdi),%rax
>     0.00 :          4996d1:       cmp    %rax,%r15
>     0.00 :          4996d4:       jne    4996e3 <lto_read_decls+0x343>
>     0.00 :          4996d6:       jmpq   4997d9 <lto_read_decls+0x439>
>     0.00 :          4996db:       nopl   0x0(%rax,%rax,1)
>     0.50 :          4996e0:       mov    %rcx,%rax
>     0.70 :          4996e3:       test   %rax,%rax
>     0.00 :          4996e6:       je     4996f9 <lto_read_decls+0x359>
>     0.00 :          4996e8:       mov    0x60(%rax),%rcx
>    98.41 :          4996ec:       cmp    %rcx,%r15
>     0.00 :          4996ef:       jne    4996e0 <lto_read_decls+0x340>
>          :                        tem = TYPE_NEXT_VARIANT (tem);
>          :                      if (tem)
>          :                        TYPE_NEXT_VARIANT (tem) = TYPE_NEXT_VARIANT
> (t);
>     0.00 :          4996f1:       mov    0x60(%r15),%rcx
>     0.00 :          4996f5:       mov    %rcx,0x60(%rax)
>          :                      TYPE_NEXT_VARIANT (t) = NULL_TREE;
>     0.00 :          4996f9:       movq   $0x0,0x60(%r15)
>          :                    }
>          :
>          :                  /* Query our new main variant.  */
>          :                  mv = gimple_register_type (TYPE_MAIN_VARIANT (t));
>     0.01 :          499701:       callq  5be860 <gimple_register_type>
>          :
>          :                  /* If we were the variant leader and we get
> replaced ourselves drop
>          :                     all variants from our list.  */
>          :                  if (TYPE_MAIN_VARIANT (t) == t
>     0.00 :          499706:       mov    0x30(%rsp),%rdx
>     0.00 :          49970b:       cmp    0x68(%rdx),%rdx
>     0.00 :          49970f:       je     4997b7 <lto_read_decls+0x417>
>          :                        }
>          :                    }
>          :
>          :                  /* If we are not our own variant leader link us
> into our new leaders
>          :                     variant list.  */
>          :                  if (mv != t)
>     0.00 :          499715:       cmp    %rax,0x30(%rsp)
>     0.00 :          49971a:       je     49992d <lto_read_decls+0x58d>
>          :                    {

That's weird.  Did the build eventually finish?  LTO bootstrap went fine
for me, but SPEC 2k6 483.xalancbmk build ran out of memory during LTRANs
(in theory we should end up using _less_ memory with the change ...)