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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-11 17:10:30 UTC ---
Created attachment 29639
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29639
gcc48-pr53265.patch

Updated version of the patch.  Haven't added docs yet.  The reason for not
warning in discover_iteration_bound_by_body_walk etc. is that I'd say the
undefined behavior warning would then be misleading, those don't detect
undefined behavior, but something else, right?  Can you think of a testcase
where we'd decrease number of iterations in those routines when it has
constant number_of_latch_iterations?
Also, with the estimate_numbers_of_loop_iterations_loop second hunk I'm not
really sure about the warning name - after all, when we warn, we actually don't
aggressively optimize anything, we aggressively optimize only when we actually
don't warn and can't easily warn.