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Re: LO_SUM memrefs offsettable ?
- To: law at cygnus dot com, Bill Currie <bcurrie at tssc dot co dot nz>
- Subject: Re: LO_SUM memrefs offsettable ?
- From: Richard Henderson <rth at cygnus dot com>
- Date: Thu, 21 Jan 1999 17:27:43 -0800
- Cc: Michael Hayes <m dot hayes at elec dot canterbury dot ac dot nz>, egcs at cygnus dot com
- References: <36A7A610.75041BDD@tssc.co.nz> <7321.916959214@hurl.cygnus.com>
- Reply-To: Richard Henderson <rth at cygnus dot com>
On Thu, Jan 21, 1999 at 03:53:34PM -0700, Jeffrey A Law wrote:
> Well, not sure. There are some ports where adding a small constant to the
> LO_SUM will work as expected -- the PA being one.
>
> Basically, there's a few bits of overlap on the PA. The "HIGH" sets the
> upper 21 bits, the LO_SUM sets the low 14 bits. Thus we can add small
> offsets directly to the LO_SUM and not lose.
Sparc as well. HIGH is the top 22, and the field containing
the LO_SUM is 13 bits.
> Actually, since HIGH & LO_SUM don't specify their size, I suspect that the
> port has to handle everything internally since there's no way to describe
> to the machine independent part of the compiler when the overlap is safe.
Indeed.
r~