On Wed, Jan 8, 2020 at 6:31 PM Richard Biener <richard.guent...@gmail.com> wrote: > > 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 I don't know either, but I simply tried to not break existing code int the patch. Function prune_uninit_phi_opnds is called for the first compares against constant, actually it should be called for each comparison, but I guess it's just avoiding O(M*N) complexity here.
> 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. IIUC, with current implementation, it's not useful to check value rang info for both sides of comparison because prune_uninit_phi_opnds requires the flag_var be defined by PHI node in the same basic block as PHI parameter. Thanks, bin > > 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.
