http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45122
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|wrong-code |diagnostic
--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-11-10
14:45:27 UTC ---
We assume the loop iterates with induction variable a from zero to
((unsigned long)((unsigned)(((int)x->b) - 8) /[ex] 8)) & 536870911 + 1
which is one iteration less than required.
The assumptions made from niter analysis for that to be valid is
((unsigned int) D.2724_6 & 7) == 0 which isn't satisfied (it's 1).
So, technically we run into
if (flag_unsafe_loop_optimizations)
niter->assumptions = boolean_true_node;
and assume the above holds true. We add this assumption here:
if (!exit_must_be_taken)
{
/* If we cannot assume that the exit is taken eventually, record the
assumptions for divisibility of c. */
assumption = fold_build2 (FLOOR_MOD_EXPR, niter_type, c, d);
assumption = fold_build2 (EQ_EXPR, boolean_type_node,
assumption, build_int_cst (niter_type, 0));
thus a proper warning wording would say sth about that reason.
