[Bug tree-optimization/23603] VRP does not say range for a in a = b == c; is [0,1]

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2007-01-07 17:44 
-------
In extract_range_from_binary we have another case where we drop to varying:

  /* For integer ranges, apply the operation to each end of the
     range and see what we end up with.  */
  if (code == TRUTH_ANDIF_EXPR
      || code == TRUTH_ORIF_EXPR
      || code == TRUTH_AND_EXPR
      || code == TRUTH_OR_EXPR)
    {
...
      else
        {
          set_value_range_to_varying (vr);
          return;
        }
    }

But the latent problems seem to be fixed, the following (simple) patch
bootstrapped and regtested ok for me:

*************** extract_range_from_comparison (value_ran
*** 1920,1926 ****
        set_value_range (vr, VR_RANGE, val, val, vr->equiv);
      }
    else
!     set_value_range_to_varying (vr);
  }


--- 1925,1933 ----
        set_value_range (vr, VR_RANGE, val, val, vr->equiv);
      }
    else
!     /* The result of a comparison is always true or false.  */
!     set_value_range (vr, VR_RANGE, build_int_cst (TREE_TYPE (expr), 0),
!                    build_int_cst (TREE_TYPE (expr), 1), vr->equiv);
  }


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23603