[Bug 279443] LIBCPP assertions are enabled in optimized builds when -DNDEBUG is given to clang

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=279443

Mark Millard <marklmi26-fbsd@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marklmi26-fbsd@yahoo.com

--- Comment #1 from Mark Millard <marklmi26-fbsd@yahoo.com> ---
I tried the code that is based on:

            std::copy(
                &buf[0],
                &buf[cb], // !!! ASSERTs HERE !!!
                std::back_inserter(r)
            );

via:

# c++ -g get_executable_filename.cpp
# gdb a.out
. . .
Reading symbols from a.out...
(gdb) run
Starting program: /usr/home/root/c_tests/a.out 

Program received signal SIGILL, Illegal instruction.
Privileged opcode.
0x0000000000203faa in std::__1::vector<char, std::__1::allocator<char>
>::operator[][abi:se180100](unsigned long) (this=0x7fffffffe940, __n=29) at
/usr/include/c++/v1/vector:1393
1393      _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n < size(), "vector[] index out
of bounds");

Then I tried that sequence based on:

            std::copy(
                &buf[0],
                //&buf[cb], // !!! ASSERTs HERE !!!
                &buf[0] + cb, 
                std::back_inserter(r)
            );

# c++ -g get_executable_filename.cpp
# gdb a.out
. . .
Reading symbols from a.out...
(gdb) run
Starting program: /usr/home/root/c_tests/a.out 
/usr/home/root/c_tests/a.out
[Inferior 1 (process 66199) exited normally]

I'm not so sure that C++ defines &buf[cb] as equivalent to &buf[0] + cb
for std::contiguous_iterator contexts relative to all issues.

cppreference.com reports for std::contiguous_iterator :

QUOTE
Semantic requirements
Let a and b be dereferenceable iterators and c be a non-dereferenceable
iterator of type I such that b is reachable from a and c is reachable from b.
The type I models contiguous_iterator only if all the concepts it subsumes are
modeled and:
std::to_address(a) == std::addressof(*a),
std::to_address(b) == std::to_address(a) + std::iter_difference_t<I>(b - a),
and
std::to_address(c) == std::to_address(a) + std::iter_difference_t<I>(c - a).
END QUOTE

&buf[0] + cb notation does avoid any suggestion of dereferencing buf[cb] at
any stage.

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