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threading jumps makes niter changed from INTEGER_CST to chrec_dont_know
- From: Eric Fisher <joefoxreal at gmail dot com>
- To: gcc at gcc dot gnu dot org
- Date: Tue, 5 Jan 2010 16:46:13 +0800
- Subject: threading jumps makes niter changed from INTEGER_CST to chrec_dont_know
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?
Thanks,
Eric.