Re: vector lightweight debug mode

[Jonathan Wakely <jwakely@redhat.com>]

On 07/10/15 21:38 +0200, François Dumont wrote:
>Hi
>
>    I completed vector assertion mode. Here is the result of the new
>test you will find in the attached patch.
>
>With debug mode:
>/home/fdt/dev/gcc/build_git/x86_64-unknown-linux-gnu/libstdc++-v3/include/debug/safe_iterator.h:375:
>Error: attempt to advance a dereferenceable (start-of-sequence) iterator 2
>steps, which falls outside its valid range.
>
>Objects involved in the operation:
>    iterator @ 0x0x7fff1c346760 {
>      type =
>__gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*,
>std::__cxx1998::vector<int, std::allocator<int> > >,
>std::__debug::vector<int, std::allocator<int> > > (mutable iterator);
>      state = dereferenceable (start-of-sequence);
>      references sequence with type 'std::__debug::vector<int,
>std::allocator<int> >' @ 0x0x7fff1c3469a0
>    }
>XFAIL: 23_containers/vector/debug/insert8_neg.cc execution test
>
>
>With assertion mode:
>/home/fdt/dev/gcc/build_git/x86_64-unknown-linux-gnu/libstdc++-v3/include/bits/stl_vector.h:1124:
>Error: invalid insert position outside container [begin, end) range.
>
>Objects involved in the operation:
>    sequence "this" @ 0x0x7fff60b1f870 {
>      type = std::vector<int, std::allocator<int> >;
>    }
>    iterator "__position" @ 0x0x7fff60b1f860 {
>      type = __gnu_cxx::__normal_iterator<int const*, std::vector<int,
>std::allocator<int> > >;
>    }
>XFAIL: 23_containers/vector/debug/insert8_neg.cc execution test

I still don't like the formatted output for the lightweight mode, it
adds a dependency on I/O support in libc, which is a problem for
embedded systems.

The idea was to just add really cheap checks and abort  :-(

Have you compared codegen with and without assertion mode? How much
more code is added to member functions like operator[] that must be
inlined for good performance?  Is it likely to affect inlining
decisions?

I suspect it will have a much bigger impact than if we just use
__builtin_abort() as I made it do originally.

If these checks become more complex then people are not going to
enable them by default, and we probably won't want to make them
enabled by _FORTIFY_SOURCE.