[Bug tree-optimization/53265] Warn when undefined behavior implies smaller iteration count

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53265



--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-11 
14:16:20 UTC ---

To warn,

1) add a flag to struct loop whether we warned for the loop already

2) in both discover_iteration_bound_by_body_walk and

maybe_lower_iteration_bound

   warn if you run into an estimate we end up using and that lowers the

   max iterations below the value returned by number_of_latch_executions ().