[Bug c++/80084] New: [7 regression] wrong code for decomposition declaration with debug iterator

[lucdanton at free dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80084

            Bug ID: 80084
           Summary: [7 regression] wrong code for decomposition
                    declaration with debug iterator
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lucdanton at free dot fr
  Target Milestone: ---

I managed to reduce to this testcase:

//----------------------------------------
#include <cassert>
#include <vector>

struct aggr {
    std::vector<int>::iterator val;
};

void decomp(aggr arg)
{
    auto& [val] = arg;

    // fires
    assert( &val == &arg.val );
}

int main()
{
    // inlined decomp
    {
        aggr arg {};
        auto& [val] = arg;

        // fine
        assert( &val == &arg.val );
    }

    decomp(aggr {});
}
//----------------------------------

The assertion in decomp fires when the program is compiled with e.g.:

    g++-trunk -std=c++1z main.cpp -D_GLIBCXX_DEBUG

According to my bisecting, this change was introduced by r245638.