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Re: question about DSE
- From: Richard Henderson <rth at redhat dot com>
- To: Alex Turjan <aturjan at yahoo dot com>
- Cc: Michael Matz <matz at suse dot de>, gcc at gcc dot gnu dot org
- Date: Wed, 09 Sep 2009 10:59:40 -0700
- Subject: Re: question about DSE
- References: <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~