On Mon, Feb 22, 2016 at 11:46:19AM +0000, Alan Lawrence wrote:
> On 19/02/16 17:52, Jakub Jelinek wrote:
> >On Fri, Feb 19, 2016 at 05:42:34PM +0000, Alan Lawrence wrote:
> >>This relates to FORTRAN code where different modules give different sizes
> >>to the
> >>same array in a COMMON block (contrary to the fortran language
> >>specification).
> >>SPEC have refused to patch the source code
> >>(https://www.spec.org/cpu2006/Docs/faq.html#Run.05).
> >>
> >>Hence, this patch provides a Fortran-specific option -funknown-commons that
> >>marks such arrays as having unknown size - that is, NULL_TREE for both
> >>TYPE_SIZE and max value of TYPE_DOMAIN. DECL_SIZE is preserved for e.g.
> >>output
> >>in varasm.c.
> >>
> >>On AArch64, it fixes the 416.gamess issue, and allows compiling 416.gamess
> >>without the -fno-aggressive-loop-optimizations previously required (numerous
> >>other PRs relating to 416.gamess).
> >>
> >>I had to fix up a couple of places to deal with null TYPE_SIZE but in most
> >>cases
> >
> >I think it is wrong to touch TYPE_SIZE/TYPE_SIZE_UNIT, IMHO it is much
> >better just
> >to ignore DECL_SIZE/DECL_SIZE_UNIT in the selected few places
> >(get_ref_base_and_extent, the tree-ssa-loop-niters.c analysis) if the switch
> >is on, for selected decls (aggregates with flexible array members and other
> >similar trailing arrays, arrays themselves; all only if DECL_COMMON).
>
> So do you see...
>
> (a) A global command-line option, which we check alongside DECL_COMMON, in
> (all or some of the) places which currently deal with flexible array
> members? (I guess the flag would have no effect for compiling C code...or
> (b) do we require it to 'enable' the existing flexible array member support?)
>
> (c) A new flag on each DECL, which we check in the places dealing with
> flexible array members, which we set on those decls in the fortran frontend
> if a fortran-frontend-only command-line option is passed?
>
> (d) A new flag on each DECL, which replaces the check for flexible array
> members, plus a global command-line option, which controls both setting the
> flag (on DECL_COMMONs) in the fortran frontend, and also setting it on
> flexible array members in the C frontend? This might be 'cleanest' but is
> also probably the most change and I doubt I'm going to have time to do this
> for GCC 6...
>
> (e) Some other scheme that I've not understood yet?
(f) A global command-line option, which we check alongside DECL_COMMON and
further tests (basically, we want only DECL_COMMON decls that either have
ARRAY_TYPE, or some other aggregate type with flexible array member or some
other trailing array in the struct), and use the resulting predicate in
places where we optimize based on DECL_SIZE{,_UNIT} of the decl - if that
predicate returns true, we assume the DECL_SIZE is
"variable"/"unlimited"/whatever.
The two spots known to me that would need to use this new predicate would
be:
tree.c (array_at_struct_end_p):
/* If the reference is based on a declared entity, the size of the array
is constrained by its given domain. */
if (DECL_P (ref))
return false;
This would need to do if (DECL_P (ref) && !the_new_predicate (ref)) return
false;
tree-dfa.c (get_ref_base_and_extent):
if (DECL_P (exp))
{
...
}
You want to do inside of that block something like
if (the_new_predicate (exp))
{
/* We need to deal with variable arrays ending structures. */
if (seen_variable_array_ref
&& maxsize != -1
&& (TYPE_SIZE (TREE_TYPE (exp)) == NULL_TREE
|| TREE_CODE (TYPE_SIZE (TREE_TYPE (exp))) != INTEGER_CST
|| (bit_offset + maxsize
== wi::to_offset (TYPE_SIZE (TREE_TYPE (exp))))))
maxsize = -1;
else if (TREE_CODE (TREE_TYPE (exp)) == ARRAY_TYPE)
maxsize = -1;
}
/* If maxsize is unknown adjust it according to the size of the
base decl. */
else if ((maxsize == -1
&& DECL_SIZE (exp)
&& TREE_CODE (DECL_SIZE (exp)) == INTEGER_CST)
maxsize = wi::to_offset (DECL_SIZE (exp)) - bit_offset;
Thus, basically for the DECL_COMMON with trailing array readd the
r233153 hunk (though it can be readded in slightly different spot),
somehow deal with the case of ARRAY_TYPE itself, and only apply DEC_SIZE if
the predicate is false.
Jakub
