Re: [PATCH] fortran: Fix up initializers of param(0) PARAMETERs [PR103691]

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Mar 25, 2022 at 12:16:40PM +0100, Richard Biener wrote:
> On Fri, Mar 25, 2022 at 11:13 AM Tobias Burnus <tobias@codesourcery.com> wrote:
> >
> > On 25.03.22 09:57, Jakub Jelinek via Fortran wrote:
> > > On the gfortran.dg/pr103691.f90 testcase the Fortran ICE emits
> > >    static real(kind=4) a[0] = {[0 ... -1]=2.0e+0};
> > > That is an invalid RANGE_EXPR where the maximum is smaller than the minimum.
> > >
> > > The following patch fixes that.  If TYPE_MAX_VALUE is smaller than
> > > TYPE_MIN_VALUE, the array is empty and so doesn't need any initializer,
> > > if the two are equal, we don't need to bother with a RANGE_EXPR and
> > > can just use that INTEGER_CST as the index and finally for the 2+ values
> > > in the range it uses a RANGE_EXPR as before.
> > >
> > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> >
> > LGTM – thanks for taking care of Fortran patches and regressions.
> >
> > > 2022-03-25  Jakub Jelinek  <jakub@redhat.com>
> > >
> > >       PR fortran/103691
> > >       * trans-array.cc (gfc_conv_array_initializer): If TYPE_MAX_VALUE is
> > >       smaller than TYPE_MIN_VALUE (i.e. empty array), throw the initializer
> > >       on the floor, if TYPE_MIN_VALUE is equal to TYPE_MAX_VALUE, use just
> > >       the TYPE_MIN_VALUE as index instead of RANGE_EXPR.
> >
> > I am not sure whether "throw the initializer on the floor" is the best wording
> > for a changelog. I think I prefer a wording like "ignore the initializer" or
> > another less idiomatic expression. And I think a ';' before the second 'if'
> > also increases readability.
> 
> Can there be side-effects in those initializer elements in Fortran?

For PARAMETERs certainly not, those need to be constant.
Even otherwise, this is in a routine that does
  /* Create a constructor from the list of elements.  */
  tmp = build_constructor (type, v);
  TREE_CONSTANT (tmp) = 1;
  return tmp;
at the end so I wouldn't expect side-effects anywhere.

Also, I think typically in the Fortran FE side-effects would go into
se.pre and se.post sequences, not into se.expr, and this routine
doesn't emit those se.pre/se.post sequences anywhere, so presumably it
assumes they don't exist.

What is the behavior with a RANGE_EXPR when one has { [0..10] = ++i; },
is that applying the side-effects 11 times or once ?


	Jakub