------- Additional Comments From steven at gcc dot gnu dot org 2005-07-14
17:02 -------
The bug is that the 4 cross operations are not computed properly. In
extract_range_from_binary_expr we compute them as follows:
/* Compute the 4 cross operations. */
val[0] = vrp_int_const_binop (code, vr0.min, vr1.min);
val[1] = (vr1.max != vr1.min)
? vrp_int_const_binop (code, vr0.min, vr1.max)
: NULL_TREE;
val[2] = (vr0.max != vr0.min)
? vrp_int_const_binop (code, vr0.max, vr1.min)
: NULL_TREE;
val[3] = (vr0.min != vr1.min && vr0.max != vr1.max)
? vrp_int_const_binop (code, vr0.max, vr1.max)
: NULL_TREE;
We compute this for "i*i" so vr0.min == vr1.min and vr0.max == vr1.max,
because vr0 and vr1 are the same (both are the range for i, which is [0,4]
at this point).
We end up with:
val[0] = <integer_cst type <integer_type "long int"> constant invariant 0>
val[1] = <integer_cst type <integer_type "long int"> constant invariant 0>
val[2] = <integer_cst type <integer_type "long int"> constant invariant 0>
val[3] = NULL_TREE
Obviously we derive that the new range for "i*i" must be "0" from these
incorrect val[] results.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22230
