BOZ, F2008 and F2015, and future of gfortran

[Steve Kargl]

On Fri, Oct 06, 2017 at 07:58:58AM +0200, Richard Biener wrote:
> On October 6, 2017 7:02:10 AM GMT+02:00, Steve Kargl <sgk@troutmask.apl.washington.edu> wrote:
> >
> >program foo
> >   integer :: i(2) = [z'124', z'bed']
> >   print *, i
> >end program foo
> >
> >First, this is nonstandard in that a BOZ-literal-constant cannot 
> >appear in the above context.  Unfortunately, the above leads
> >to an ICE.  I need to figure how to walk the array constructor
> >and have gfortran use the type and type kind parameter of the
> >lhs to convert the rhs boz. 
> 
> I'm just guessing the semantics but you might find native_encode/interpret_expr useful in this context. 
> 

I can handle the needed transformation in the Fortran FE
once I figure out how we handle array constructors.  In
Fortran, [z'124', z'bed'] is an array constructor and 
Fortran forbids a BOZ from appearing here.  This is 
currently allowed in gfortran, because gfortran upon 
parsing a BOZ immediately converts it to an INTEGER(N)
(with N=8 or 16 depending on target).  My patch
gives a BOZ a basic type of BT_BOZ, which is new and
treated as a typeless sequence of bits.  I need to catch
an entity with a BT_BOZ basic type and do essentially a
JIT conversion to the correct type when translating an
array constructor.  Unfortunately, gdb sessions suggest
that we have a use-after-free bug lurking.  

-- 
Steve
20170425 https://www.youtube.com/watch?v=VWUpyCsUKR4
20161221 https://www.youtube.com/watch?v=IbCHE-hONow