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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.arch
Subject: Re: MIPS's machine
Message-ID: <6617@utzoo.UUCP>
Date: Thu, 24-Apr-86 15:14:24 EST
Article-I.D.: utzoo.6617
Posted: Thu Apr 24 15:14:24 1986
Date-Received: Thu, 24-Apr-86 15:14:24 EST
References: <6593@utzoo.UUCP>, <17418@rochester.ARPA>
Organization: U of Toronto Zoology
Lines: 17

> >...  Load and
> >store instructions come in a number of flavors, including hardware help
> >for unaligned references:  you need two instructions to pick up the two
> >pieces of the data, but then you'd need two memory cycles anyway...
> 
> Unfortunately, you need to know that the reference is unaligned.  This
> will involve some runtime checks if unaligned references are allowed.

What it will involve, probably, is a compiler switch saying "generate all
references as aligned" or "generate all references you cannot be certain
about as unaligned".  In other words, only programs that must be able to
do unaligned references have to pay for it.  (This is a guess, not based
on official information from MIPS, but seems plausible.)  I like it.
-- 
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