[Bug rtl-optimization/63156] web can't handle AUTOINC correctly

[carrot at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63156

--- Comment #6 from Carrot <carrot at google dot com> ---
(In reply to Steven Bosscher from comment #5)
> (In reply to Carrot from comment #4)
> > For a AUTOINC rtl expression, we create two refs, one def and one use, but
> > only the def gets the flag DF_REF_READ_WRITE, the use doesn't have this flag.
> 
> Then this is fall-out of PR32339.

Since it is intentionally to remove flag DF_REF_READ_WRITE on use, in web_main
we should also check all defs with flag DF_REF_READ_WRITE, union it with
corresponding use.