Re: IPA merge 6: variable annotations

[Diego Novillo <dnovillo at redhat dot com>]

Jan Hubicka wrote on 12/03/06 18:54:

> How would sound putting dense UIDs to each referenced var into the
> annotations implemented by direct pointers/hashtable as I am doing now
> and using on-side arrays/bitmaps in the passes? (pretty much as we do
> for REGNOs on RTL land).
Yes, I have wanted to try this for the longest time.  A dense DECL_UID
space would allow us to use simple arrays like we do with SSA_NAMEs.

> I remember disucssing the variable UIDs with Kenny and others on GCC
> summit and we was considering some strategies for static numbering (ie
> giving global UIDs in a way so each function has just limited range),
> but I think we found out this is not going to work in all cases when we
> want to invent new local and global variables on the go.  So it seem to
> me the hashtable assinging static's the local UIDs is probably best
> solution here for local passes, we still can use DECL_UID for purposes
> of IPA datastructures.
How about an UID that is a tuple <fnid, declid> so that each
function can add temporary variables?  The tuple could be encoded as a
HOST_WIDE_INT split into M bits for fnid and N bits for declid, or it
could be a structure of two ints.

Each pass would then have a matrix where to store DECL annotations.

> + 
> + /* Hashtable of variables annotations.  Used for static variables only;
> +    local variables have direct pointer in the tree node.  */
> + static inline htab_t
> + gimple_var_anns (struct function *fun)
Spacing.  Document argument FUN.  Similarly in other functions.

This is OK in the meantime.  I think an array of annotations and
dual ID numbering should work in the long term.