Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!cmcl2!yale!mfci!colwell
From: colwell@mfci.UUCP (Robert Colwell)
Newsgroups: comp.arch
Subject: multiple register windows
Message-ID: <536@m3.mfci.UUCP>
Date: 28 Oct 88 12:41:56 GMT
References: <156@gloom.UUCP> <310@lynx.zyx.SE> <332@pvab.UUCP> <15964@agate.BERKELEY.EDU> <23367@amdcad.AMD.COM> <16003@agate.BERKELEY.EDU> <469@oracle.UUCP> <16054@agate.BERKELEY.EDU>
Sender: colwell@mfci.UUCP
Reply-To: colwell@mfci.UUCP (Robert Colwell)
Organization: Multiflow Computer Inc., Branford Ct. 06405
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In article <16054@agate.BERKELEY.EDU> matloff@iris.ucdavis.edu (Norm Matloff) writes:
>*If I remember the arguments from MIPS correctly (want to help me out
>*John?), there's a stronger objection to multiple-window-register-files.
>*I think it's something to the effect that register-windows cause the
>*load/store access time to be slower.  I think there also may be some
>*argument that a good compiler makes multiple-windows relatively
>*unnecessary.
>
>A compiler which automatically inlines procedure calls might be able
>to do what you are saying.  However, there may be some unpleasant
>side effects, depending on the language.  Actually, one of my grad
>students in making a thesis out of this, so I'll try to report more
>on it later.

Don't forget that one of the side effects of having your registers
arranged into windows is that you don't have access to very many 
registers from within any given procedure.  There are routines
that need lots of them, and there are routines that need very
few.  The one-size-fits-all approach is not what a good compiler
wants; it would rather see them all at once and do the management
explicitly.  The windowing is just a hack to make parameter-passing
cheap, which a compiler can do just as well or better.

Bob Colwell            mfci!colwell@uunet.uucp
Multiflow Computer
175 N. Main St.
Branford, CT 06405     203-488-6090