Question about generated type for common block in fortran

[Richard Biener]

On Wed, Nov 8, 2017 at 3:45 PM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Wed, 8 Nov 2017, Richard Biener wrote:
>
>> Not sure how - the issue is the FIELD_DECLs overlap which rules out a
>> RECORD_TYPE and leaves us with a UNION_TYPE.
>
> No, as the initial mail already mentioned, for the example in
> question the overlapping fields can be put into a union which itself is
> part of a struct:
>
> struct S {
>   union { T mem1[len]; T overlap1[len]; };
>   union { T mem2[len]; T overlap2[len]; };
> };
>
> If you do real fancy equivalences with partial overlaps then you're right,
> the type necessarily will look strange then.  But for this example the
> type could be improved (if that helps anything I don't know, though).

Sure - for some cases the type representation can be improved, but
generally we either have to go the BIT_FIELD_REF route or not assume
that union members start at offset zero and thus not multiple ones can
be live at the same time.

Richard.

>
> Ciao,
> Michael.