[Bug c++/56671] New: Gcc uses large amounts of memory and processor power with large C++11 bitsets

[Bug c++/56671] New: Gcc uses large amounts of memory and processor power with large C++11 bitsets

[m101010a at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56671

             Bug #: 56671
           Summary: Gcc uses large amounts of memory and processor power
                    with large C++11 bitsets
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: m101010a@gmail.com


When I attempt to instantiate std::bitset<1024*1024*1024> in C++98 mode,
compilation takes a quarter-second and uses almost no RAM.  In C++11 mode, it
takes 8 seconds and almost 2GB of RAM.  The time and memory usage appear to
scale linearly with the size of the bitset.  No errors or warnings are reported
in either mode.

Full code:
#include <bitset>
int main()
{
    std::bitset<1024*1024*1024> bs;
}

Compilation lines:
g++ -std=c++98 x.cpp
g++ -std=c++11 x.cpp

g++ -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/src/gcc-4.7.2/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--enable-libstdcxx-time --enable-gnu-unique-object --enable-linker-build-id
--with-ppl --enable-cloog-backend=isl --disable-ppl-version-check
--disable-cloog-version-check --enable-lto --enable-gold --enable-ld=default
--enable-plugin --with-plugin-ld=ld.gold --with-linker-hash-style=gnu
--enable-multilib --disable-libssp --disable-build-with-cxx
--disable-build-poststage1-with-cxx --enable-checking=release
Thread model: posix
gcc version 4.7.2 (GCC)

[Bug c++/56671] Gcc uses large amounts of memory and processor power with large C++11 bitsets

[markus at trippelsdorf dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56671

--- Comment #1 from Markus Trippelsdorf <markus at trippelsdorf dot de> 2013-03-21 08:31:57 UTC ---
Created attachment 29703
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29703
callgraph

Looks like a bug in constant expression handling.

perf shows:
 15.51%   cc1plus  cc1plus            [.] gt_ggc_mx_lang_tree_node(void*)
 11.14%   cc1plus  cc1plus            [.] walk_tree_1(tree_node**, tree_node*
(*)(tree_node**, int*, void*), void*, pointer_set_t*, tree_node*
(*)(tree_node**, int*, tree_no
  9.54%   cc1plus  cc1plus            [.] htab_expand.1557810
  7.28%   cc1plus  cc1plus            [.] ggc_set_mark(void const*)
  6.35%   cc1plus  cc1plus            [.] lookup_page_table_entry(void const*)
[clone .218759]
  6.32%   cc1plus  cc1plus            [.] build_int_cst(tree_node*, long)
  5.07%   cc1plus  [kernel.kallsyms]  [k] clear_page_c
  3.60%   cc1plus  cc1plus            [.]
initializer_constant_valid_p_1(tree_node*, tree_node*, tree_node**) [clone
.1222026]
  3.46%   cc1plus  cc1plus            [.] mostly_copy_tree_r(tree_node**, int*,
void*) [clone .459380]
  2.57%   cc1plus  cc1plus            [.] gt_ggc_mx(constructor_elt_d&)
  2.21%   cc1plus  cc1plus            [.] vec<constructor_elt_d, va_gc,
vl_embed>::copy() const [clone .local.823]
  1.97%   cc1plus  cc1plus            [.] int_cst_hash_hash(void const*) [clone
.1202876]
  1.94%   cc1plus  cc1plus            [.] cxx_eval_vec_init_1(constexpr_call
const*, tree_node*, tree_node*, bool, bool, bool, bool*, bool*) [clone
.109131.20812] 


cxx_eval_outermost_constant_expr -> cxx_eval_constant_expression ->
-> cxx_eval_vec_init_1 -> build_int_cst 
(see attached callgraph)

[Bug c++/56671] Gcc uses large amounts of memory and processor power with large C++11 bitsets

[tudorb at fb dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56671

Tudor Bosman <tudorb at fb dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tudorb at fb dot com

--- Comment #2 from Tudor Bosman <tudorb at fb dot com> ---
We're encountering the same with huge (16M elements) std::array, I presume the
issue is the same.