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Re: threading jumps makes niter changed from INTEGER_CST to chrec_dont_know
- From: Richard Guenther <richard dot guenther at gmail dot com>
- To: Eric Fisher <joefoxreal at gmail dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 5 Jan 2010 11:56:10 +0100
- Subject: Re: threading jumps makes niter changed from INTEGER_CST to chrec_dont_know
- References: <d6afecde1001050046l4363043bt504be33a6cec2cf3@mail.gmail.com>
On Tue, Jan 5, 2010 at 9:46 AM, Eric Fisher <joefoxreal@gmail.com> wrote:
> Hi,
>
> I found that sometimes -fno-tree-dominator-opts will bring a big speed
> promotion. This is because that pass_dominator tries to thread jumps.
> But sometimes this will cause that the loop's exit bb does not
> dominator its latch bb again. Then pass_complete_unroll is unable to
> know the exact number of loop iteration and will not unroll the loop
> completely again
>
> Any comments?
Do you have a testcase for this? Please file a bugreport then. Jump threading
should avoid breaking canonical loop forms.
Thanks,
Richard.
> Thanks,
> Eric.
>