[Bug middle-end/31795] New: -Wunused should warn about variables set but never read

["ghazi at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Patches like this:
http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00059.html

expose a problem with GCC's -Wunused machinery.  Namely, that it fails to
detect cases where a variable is set but never read.  I'd like GCC to detect
these cases automatically.  I think it probably requires auditing everywhere
the TREE_USED flag is set, and splitting it into a TREE_READ vs. a
TREE_ASSIGNED flag.  Or something like that.  Then we could distinguish these
two cases and issue the appropriate warning for cases like in the above URL.

Seems like there's about 150 "TREE_USED.*=" across the whole source base. 
That's a lot, but not insurmountable.

IIRC, the SGI compiler had this ability many years ago.  It would be nice IMHO
if we caught up in this regard.


-- 
           Summary: -Wunused should warn about variables set  but never read
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ghazi at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31795