[Bug fortran/48419] Reduce gfortran stack usage for procedures doing IO

[jb at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48419

--- Comment #1 from Janne Blomqvist <jb at gcc dot gnu.org> 2011-04-02 21:12:25 UTC ---
(In reply to comment #0)
> For #2 there are a few options. Say,
> 
> a) A char array containing all the data. Walk over the flags variable, and for
> each set bit, read the appropriate number of bytes from the char array and bump
> a pointer to the current position. This is probably the most space efficient,
> but might run into alignment issues on some targets? So maybe one needs to
> memcpy() the data to some properly aligned data before actually using it.
> 
> b) Create a union of all the specifier data structs. Then pass an array of this
> union type, with the flags variable specifying the type of each element (that
> is, the length of the array is the number of set bits in the flag variable).
> This might waste a bit of space compared to the previous approach, but should
> ensure that everything is properly aligned. From a brief scan of current
> sources, the biggest element is probably for character variables, which is a
> pointer to the string and the length, so in no case will the union type be
> particularly large.
> 
> c) Get rid of the flags variable, and instead pass a variable specifying the
> array length, the array elements being a struct of an enum specifying the
> element type, and the union type described in the previous approach.
> 
> Personally, I think option c) looks the cleanest.

I meant that I'd prefer b), not c). In any case, whichever is preferred also
depends on what is easy-ish to do in the frontend.