Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!mips!winchester!mash From: mash@mips.COM (John Mashey) Newsgroups: comp.arch Subject: Re: What *should* architectural pointers point at? Message-ID: <41167@mips.mips.COM> Date: 29 Aug 90 06:00:33 GMT References: <0887@sheol.UUCP> Sender: news@mips.COM Reply-To: mash@mips.COM (John Mashey) Organization: Your Organization Goes Here Lines: 39 In article <0887@sheol.UUCP> throopw@sheol.UUCP (Wayne Throop) writes: >Surely bit-granular addressing is the only sensible way to go... what >reasons are against it in a 64-bit world? I doubt this is the only sensible way to go, but it does lead to an interesting exercise. First, let us observe that with 64-bit addressing, one could afford to sacrifice 3 bits for this, which is probably not true in the 32-bit world. However, for concreteness, and ease of looking at it, let's think about the 32-bit version. So here's the exercise: 1) Start with any of the popular RISC architectures (or a synthetic, like P&H's DLX). 2) Change the addressing so it uses bit-addressing. 3) (Architecture): what must you change? what instructions would be added or deleted? are there common code sequences that would change? for better, for worse. 4) Implementation: are there any interesting critical-path or area layout issues that show up? 5) Software: which existing languages can make use of this feature, and how? Which languages can PORTABLY make use of this feature, i.e., least-common-denominator theory of software causes most people to avoid unusual features unless there's a big benefit. Are there language extensions one would propose that can portably take advantage of such features? ------ Note: it would probably good to make the assumption that if an architecture traps on unaligned accesses that it would continue to do so. -- -john mashey DISCLAIMER: UUCP: mash@mips.com OR {ames,decwrl,prls,pyramid}!mips!mash DDD: 408-524-7015, 524-8253 or (main number) 408-720-1700 USPS: MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086