[Bug tree-optimization/71466] [7 Regression] wrong code at -O3 on x86_64-linux-gnu

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71466

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |hubicka at gcc dot gnu.org

--- Comment #7 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Isn't the problem caused by fact that you end up rolling the loop and thus
increasing number of iterations? Number of iterations is number of execution of
the edge latch->header and is stored perisstently in the loop structure.
If you change shape of the loop and some earlier edge becomes latch, you may
need to adjust the estimate.

If you are busy, I may try to look into this at weekend. I quite like the new
threading code becuase it is simple while it catch many cases in practice. If
it had mode that does not increase code size (which I sent patch for) it may be
a good candidate for an early pass getting profile estimation to work
noticeably better.

Honza