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Re: Copying SI regs as HI subregs
- From: Michael Hayes <m dot hayes at elec dot canterbury dot ac dot nz>
- To: "D. Towner" <towner at cs dot bris dot ac dot uk>
- Cc: gcc <gcc at gcc dot gnu dot org>
- Date: Fri, 01 Mar 2002 23:53:48 +1300
- Subject: Re: Copying SI regs as HI subregs
- References: <Pine.GSO.4.33.0202281019280.22323-100000@tao>
D. Towner writes:
> Is it more efficient to use RTL to generate the two subreg moves
> explicitly? Does this present opportunities for optimisation if gcc knows
> that two such instructions are used, rather than a single atomic movsi
> instruction? How can I go about actually generating the RTL if this is the
> case?
At the moment you are probably better off by not exposing this too
early. You should use a splitter pattern predicated on
reload_completed. However, you will miss some low level insn
combination opportunities which hopefully the proposed RTL lowering
scheme should avoid.
Michael.