Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!pt.cs.cmu.edu!sei!firth
From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: comp.arch
Subject: Re: 64-bit addresses
Message-ID: <6190@bd.sei.cmu.edu>
Date: 21 Feb 90 19:07:52 GMT
References: <9708@spool.cs.wisc.edu> <20270@cfctech.cfc.com> <11112@encore.Encore.COM> <10795@snow-white.udel.EDU> <2027@osc.COM> <162@gollum.twg.com> <2054@osc.COM>
Reply-To: firth@sei.cmu.edu (Robert Firth)
Organization: Software Engineering Institute, Pittsburgh, PA
Lines: 18

In article <2054@osc.COM> jgk@osc.osc.COM (Joe Keane) writes:

>I agree this [ pooling constants]
 is hard, but it's an interesting optimization and can only
>improve your performance.  Of course it's completely impossible if your
>constants are embedded in the instruction stream.

Sorry, I don't see that.  Since the average constant is smaller than
the average address, taking constants out of line and pooling them
seems to me a guaranteed pessimisation

(a) you don't save bits in the instruction, and may need more

(b) the extra indirection is one more memory reference, which
    is pure overhead

(c) you have reduced locality by adding a gratuitous reference to
    another part of the address space