[Bug tree-optimization/31178] VRP can infer a range for b in a >> b and a << b

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

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-03-15 14:43 -------
This is blocked by the same fact as PR30317 in that ASSERT_EXPRs can only
assert half-ranges or single valued ranges.  This makes the following prototype
not assert [0, prec) but [-INF, prec) instead :(

Index: tree-vrp.c
===================================================================
*** tree-vrp.c  (revision 122953)
--- tree-vrp.c  (working copy)
*************** infer_value_range (tree stmt, tree op, e
*** 3113,3118 ****
--- 3113,3134 ----
        }
      }

+   /* We can assume that the shift argument of a left or right shift
+      is within zero and the type precision of the shifted operand.  */
+   if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT
+       && (TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 1)) == RSHIFT_EXPR
+         || TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 1)) == LSHIFT_EXPR)
+       && TREE_OPERAND (GIMPLE_STMT_OPERAND (stmt, 1), 1) == op)
+     {
+       tree lop = TREE_OPERAND (GIMPLE_STMT_OPERAND (stmt, 1), 0);
+       tree lop_type = TREE_TYPE (lop);
+ 
+       /* Unfortunately we only can infer half-ranges here.  */
+       *val_p = build_int_cst (lop_type, TYPE_PRECISION (lop_type) - 1);
+       *comp_code_p = LE_EXPR;
+       return true;
+     }
+ 
    return false;
  }



-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |30317


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31178