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[Bug tree-optimization/23619] Missed pre opportunity
- From: "dberlin at dberlin dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 29 Aug 2005 15:23:15 -0000
- Subject: [Bug tree-optimization/23619] Missed pre opportunity
- References: <20050829090219.23619.rakdver@gcc.gnu.org>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From dberlin at gcc dot gnu dot org 2005-08-29 15:23 -------
Subject: Re: Missed pre opportunity
> Disabling reassoc, it knows that p + q is antic over the backedge.
> Which means it knows it *could* insert it.
Okay, it determines it's not fully available in block 6, even though
both predecessors of 6 generate it, because neither predecessor strictly
dominates block 6, and nowhere else that generates the expression does.
This is a partial partial case that i never bothered handling because it
just doesn't happen often in practice, AFAICT.
We can do it, and i know how, it just was never worth it.
We'd have to generate a no-cost phi in block 6 to merge the two
available values.
Let me see if i can change compute_avail to do this for us so we don't
have to worry about it later.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23619