[Bug c++/77550] New: std::deque with -O3 has infinite std::distance

[dan.cooke89 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77550

            Bug ID: 77550
           Summary: std::deque with -O3 has infinite std::distance
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dan.cooke89 at gmail dot com
  Target Milestone: ---

The following program, compiled with -O3, never returns:

#include <string>
#include <deque>
#include <iterator>
#include <iostream>

#include <boost/iterator/filter_iterator.hpp>

struct Foo
{
    std::string bar, s = "";
    char a = '\0';
};

int main()
{
    const std::deque<Foo> foos(14, {""});
    const std::string test {};
    const auto p = [test] (const auto& foo) { return foo.bar == test; };
    using boost::make_filter_iterator;
    const auto begin = make_filter_iterator(p, std::cbegin(foos),
std::cend(foos));
    const auto end   = make_filter_iterator(p, std::cend(foos),
std::cend(foos));
    std::cout << std::distance(begin, end) << std::endl;
}

Observations:

 - GCC with optimisations -O2 or less returns as expected.
 - Clang (3.8) returns the correct answer with any optimisation level.
 - Changing std::deque to std::vector or std::list results in expected
behaviour.
 - The 14 is critical; anything less and the problem disappears.
 - The sizeof(Foo) is important; removing s or a makes the problem go away.
 - Capturing test by reference, or just comparing to a constant expression
(e.g. foo.bar == " ") results in normal behaviour.
 - There are no compiler warnings (with -Wall -Wextra -pedantic).
 - Valgrind reports no errors.
 - Use fsanitize=undefined and the problem goes away.

From: http://stackoverflow.com/q/39424753/2970186