[Bug fortran/85526] New: [6.4 regression] calling a (pure) function from inside another pure function may cause segmentation fault during compilation

[mail at pietrodelugas dot it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85526

            Bug ID: 85526
           Summary: [6.4 regression] calling a (pure) function from inside
                    another  pure function may cause segmentation fault
                    during compilation
           Product: gcc
           Version: 6.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mail at pietrodelugas dot it
  Target Milestone: ---

Created attachment 44019
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44019&action=edit
fortran source file to demonstrate the bug

A call to a pure function from inside a pure function crashes the compilation
with this message 

internal compiler error: Segmentation fault

the same code has been compiling regularly with gfortran up to 6.2 while it is
failing in 6.4 and 7.3 versions 

I attach a sample source file