Re: [PATCH] Fold VIEW_CONVERT_EXPR <type, STRING_CST> generated by Fortran FE a lot (PR target/35366)

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

On Tue, Nov 11, 2008 at 04:45:40PM +0100, Tobias Schlüter wrote:
> Jakub Jelinek wrote:
> >Unfortrunately, it causes 2 Fortran testsuite failures, hollerith.f90
> >and transfer_simplify_4.f90, both at all optimization levels.
> >I believe the tests are just invalid though.  The first one does:
> >logical l
> >l = 4Ho wo
> >and expects all the 32 bits preserved, but that is certainly against
> >the semantics of BOOLEAN_TYPE and from quick skimming of the Fortran
> >standard also LOGICAL type.  BOOLEAN_TYPE has just two values, false
> >and true (similarly for LOGICAL .false. and .true.) and so the folder
> >IMHO correctly folds this into
> >l = .true.
> >(4Ho wo is non-zero).  The transfer_simplify_4.f90 testcase transfers an
> >integer into logical and back and expects again all the 32-bits to be
> >preserved.
> >
> >Fortran folks, can you please look at these 2 testcases and say whether
> >they are valid Fortran or just undefined behavior?
> 
> They are not standard Fortran.  Using Hollerith constants this way was 
> the way of encoding strings before there was a Character type in 
> Fortran, so the current behavior is intentional.  Whether there actually 
> is code that uses logicals to encode strings, I can't tell.  I CCed Feng 
> Wang who added the original Hollerith support, and Steve who last 
> modified the testcase.
> 

My changes in hollerith.f90 were of the form 'complex*16 --> complex(kind=8)'.
It would not have any affect on Jakub proposed patched.

In reviewing the thread, it appears that gfortran may need
to abandon BOOLEAN_TYPE because the description of TRANSFER is
quite clear:

   If D and E are scalar variables such that the physical representation 
   of D is as long as or longer than that of E, the value of
   TRANSFER (TRANSFER (E, D), E) shall be the value of E. 

unless gfortran can provide a special case for the above.  Also, note
that

   integer f, e
   logical d
   e = 42
   f = transfer(transfer(e,d),e)
   if (f /= e) abort()
   end

and

   integer f, e
   logical d
   e = 42
   d = transfer(e,d) 
   f = transfer(d,e)
   if (f /= e) abort()
   end

can be argued to have different results because the latter has two 
explicitly assignments and hence type conversions whereas the 
former has only a single assignment with an accompanying type 
conversion.

-- 
Steve