On Wed, Jan 8, 2020 at 6:01 AM bin.cheng <bin.ch...@linux.alibaba.com> wrote: > > Sorry, here is the patch. > ------------------------------------------------------------------ > Sender:bin.cheng <bin.ch...@linux.alibaba.com> > Sent At:2020 Jan. 8 (Wed.) 12:58 > Recipient:GCC Patches <gcc-patches@gcc.gnu.org> > Subject:[PATCH GCC11]Improve uninitialized warning with value range info > > > Hi, > > Function use_pred_not_overlap_with_undef_path_pred of > pass_late_warn_uninitialized > checks if predicate of variable use overlaps with predicate of undefined > control flow path. > For now, it only checks ssa_var comparing against constant, this can be > improved where > ssa_var compares against another ssa_var with value range info, as described > in comment: > > + /* Check value range info of rhs, do following transforms: > + flag_var < [min, max] -> flag_var < max > + flag_var > [min, max] -> flag_var > min > + > + We can also transform LE_EXPR/GE_EXPR to LT_EXPR/GT_EXPR: > + flag_var <= [min, max] -> flag_var < [min, max+1] > + flag_var >= [min, max] -> flag_var > [min-1, max] > + if no overflow/wrap. */ > > This change can avoid some false warning. Bootstrap and test on x86_64, any > comment?
Definitely a good idea - the refactoring makes the patch hard to follow though. The original code seems to pick any (the "first") compare against a constant. You return the "first" but maybe from range info that might also be [-INF,+INF]. It seems that we'd want to pick the best so eventually sort the predicate chain so that compares against constants come first at least? Not sure if it really makes a difference but even currently we could have i < 5, i < 1 so the "better" one later? It might also make sense to simply push three predicates for i < j, namely i < j (if ever useful), i < min(j) and max(i) < j to avoid repeatedly doing the range computations. Thanks, Richard. > Thanks, > bin > > 2020-01-08 Bin Cheng <bin.li...@linux.alibaba.com> > > * tree-ssa-uninit.c (find_var_cmp_const): New function. > (use_pred_not_overlap_with_undef_path_pred): Call above.
