https://issues.dlang.org/show_bug.cgi?id=13240

          Issue ID: 13240
           Summary: semantic3 for FormatSpec!char is extremely slow (takes
                    ~40ms)
           Product: D
           Version: unspecified
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: Phobos
          Assignee: nobody@puremagic.com
          Reporter: code@dawg.eu

It probably triggers some very inefficient compiler behavior.

--