https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64322
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- For VRP I'm thinking of (completely untested): --- gcc/tree-vrp.c.jj 2014-12-01 14:57:30.000000000 +0100 +++ gcc/tree-vrp.c 2014-12-16 10:17:27.543111649 +0100 @@ -2434,6 +2434,7 @@ extract_range_from_binary_expr_1 (value_ && code != MAX_EXPR && code != PLUS_EXPR && code != MINUS_EXPR + && code != RSHIFT_EXPR && (vr0.type == VR_VARYING || vr1.type == VR_VARYING || vr0.type != vr1.type @@ -2948,6 +2949,15 @@ extract_range_from_binary_expr_1 (value_ { if (code == RSHIFT_EXPR) { + /* Even if vr0 is VARYING or otherwise not usable, we can derive + useful ranges just from the shift count. E.g. + x >> 63 for signed 64-bit x is always [-1, 0]. */ + if (vr0.type != VR_RANGE || symbolic_range_p (&vr0)) + { + vr0.type = type = VR_RANGE; + vr0.min = vrp_val_min (expr_type); + vr0.max = vrp_val_max (expr_type); + } extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1); return; }