From: Richard Henderson <rth@redhat.com>
To: Alex Turjan <aturjan@yahoo.com>
Cc: Michael Matz <matz@suse.de>, gcc@gcc.gnu.org
Subject: Re: question about DSE
Date: Wed, 09 Sep 2009 17:59:00 -0000 [thread overview]
Message-ID: <4AA7ED0C.7000607@redhat.com> (raw)
In-Reply-To: <589093.37887.qm@web62408.mail.re1.yahoo.com>
On 09/09/2009 09:59 AM, Alex Turjan wrote:
> 1.What do you think about this implementation? using define_insn_and_split
If this port uses BITS_PER_WORD=16, then the lower-subreg pass may
be able to give you better register allocation by disconnecting the
low and high parts of the 32-bit value.
If this port uses BITS_PER_WORD=32, then lower-subreg can't do
anything, and you may get better assembly by using the post-reload
splitter.
> 2.Is is true that in the define_expand constructs I should avoid inducing subregs?
It's true that you should *always* avoid calling gen_rtx_SUBREG
directly, and instead use one of gen_lowpart, gen_highpart, or
simplify_gen_subreg.
r~
prev parent reply other threads:[~2009-09-09 17:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-08 9:57 Alex Turjan
2009-09-08 10:25 ` Andrew Haley
2009-09-08 10:55 ` Michael Matz
2009-09-09 16:59 ` Alex Turjan
2009-09-09 17:59 ` Richard Henderson [this message]
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