[Bug c++/60976] Compilation with G++ 4.9.0 is 2-3 times slower than with 4.8.2

[ott at fb dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60976

--- Comment #36 from Giuseppe Ottaviano <ott at fb dot com> ---
(In reply to Jonathan Wakely from comment #35)
> I've backported the std::allocator_traits<std::allocator<T>> partial
> specialization to the gcc-4.9 and gcc-5 branches now. Please let me know if
> this makes any difference for your use cases (and provide testcases to
> reproduce problems if not).

I reported our relative build times with my version of the partial
specialization a few comments above:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60976#c26 .
Your partial specialization patch causes an ICE in our version of GCC 4.9:

    <include_dir>/bits/alloc_traits.h:464:56: internal compiler error: in
retrieve_specialization, at cp/pt.c:1057
    0x5615cf retrieve_specialization
        <src_dir>/gcc/cp/pt.c:1054
    0x57809e tsubst_decl
        <src_dir>/gcc/cp/pt.c:11079
    0x56a9b4 tsubst(tree_node*, tree_node*, int, tree_node*)
        <src_dir>/gcc/cp/pt.c:11559
    0x570db4 instantiate_template_1
        <src_dir>/gcc/cp/pt.c:15586
    0x570db4 instantiate_template(tree_node*, tree_node*, int)
        <src_dir>/gcc/cp/pt.c:15636
    0x56a918 instantiate_alias_template
        <src_dir>/gcc/cp/pt.c:15666
    0x56a918 tsubst(tree_node*, tree_node*, int, tree_node*)
        <src_dir>/gcc/cp/pt.c:11586
    0x56fef0 lookup_template_class_1
        <src_dir>/gcc/cp/pt.c:7675
    0x56fef0 lookup_template_class(tree_node*, tree_node*, tree_node*,
tree_node*, int, int)
        <src_dir>/gcc/cp/pt.c:7901
    0x541e43 make_typename_type(tree_node*, tree_node*, tag_types, int)
        <src_dir>/gcc/cp/decl.c:3459
    0x56b49a tsubst(tree_node*, tree_node*, int, tree_node*)
        <src_dir>/gcc/cp/pt.c:12189
    0x577ec1 tsubst_decl
        <src_dir>/gcc/cp/pt.c:11110
    0x56a9b4 tsubst(tree_node*, tree_node*, int, tree_node*)
        <src_dir>/gcc/cp/pt.c:11559
    0x566fd6 tsubst_expr
        <src_dir>/gcc/cp/pt.c:13509
    0x566dbc tsubst_expr
        <src_dir>/gcc/cp/pt.c:13452
    0x56705f tsubst_expr
        <src_dir>/gcc/cp/pt.c:13657
    0x566dbc tsubst_expr
        <src_dir>/gcc/cp/pt.c:13452
    0x56705f tsubst_expr
        <src_dir>/gcc/cp/pt.c:13657
    0x57a7a4 instantiate_decl(tree_node*, int, bool)
        <src_dir>/gcc/cp/pt.c:19980
    0x57ee0b instantiate_pending_templates(int)
        <src_dir>/gcc/cp/pt.c:20096
    Please submit a full bug report,
    with preprocessed source if appropriate.
    Please include the complete backtrace with any bug report.
    See <http://gcc.gnu.org/bugs.html> for instructions.

Changing the definitions of rebind_alloc and rebind_traits to the following:

      template<typename _Tp1>
        using rebind_alloc = typename allocator_type::template
rebind<_Tp1>::other;
      template<typename _Tp1>
        using rebind_traits = allocator_traits<rebind_alloc<_Tp1>>;

fixes the ICE and matches the build time of my patch.