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Re: Why can't CSE recognize const_int's in HIGH LO_SUM pair?
- To: law at redhat dot com
- Subject: Re: Why can't CSE recognize const_int's in HIGH LO_SUM pair?
- From: Richard Henderson <rth at redhat dot com>
- Date: Mon, 10 Sep 2001 10:44:03 -0700
- Cc: John David Anglin <dave at hiauly1 dot hia dot nrc dot ca>, Bernd Schmidt <bernds at redhat dot com>, gcc at gcc dot gnu dot org
- References: <20010910095948.A8881@redhat.com> <25601.1000142996@localhost.localdomain>
On Mon, Sep 10, 2001 at 11:29:56AM -0600, law@redhat.com wrote:
> True. But with the way things are currently implemented I don't think
> we actually lose anything on the PA by not exposing the subexpressions
> to gcse. Instead of commonizing the HIGH and LO_SUM parts with other
> idential ones elsewhere, we end up commonizing (set (reg) (const_int))
Consider
(set (reg A) (const_int 0x10001))
(set (reg B) (const_int 0x10002))
as
(set (reg T) (const_int 0x10000))
(set (reg A) (plus (reg T) (const_int 1)))
(set (reg B) (plus (reg T) (const_int 2)))
Now consider A and B loaded on two different paths. Code motion can
then pull T up into the dominator.
r~