https://issues.dlang.org/show_bug.cgi?id=13420

          Issue ID: 13420
           Summary: double.nan unusable as AA key
           Product: D
           Version: D2
          Hardware: Other
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: DMD
          Assignee: nobody@puremagic.com
          Reporter: thecybershadow@gmail.com

void main()
{
    bool[double] aa;
    aa[double.nan] = true;
    assert(double.nan in aa);
}

Introduced in https://github.com/D-Programming-Language/druntime/pull/522

--