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From: lindsay@gandalf.cs.cmu.edu (Donald Lindsay)
Newsgroups: comp.arch
Subject: VAX RISC
Message-ID: <10948@pt.cs.cmu.edu>
Date: 1 Nov 90 04:23:45 GMT
Organization: Carnegie-Mellon University, CS/RI
Lines: 19


DEC has announced that it will build a "VAX RISC". I haven't heard
any details: so, let's speculate.

The killer problem is migrating the existing code. First, some of it
is in assembler, so we would want a tool which turns VAX into VAX-R
(RAX?). The tool doesn't have to generate great code: but it has to
be correctness-preserving, or else know when it's stuck. Being stuck
is OK only if it happens very rarely.

Given the tool as a constraint:  what could RAXen look like?  A MIPS
with stack-based calling convention and non-IEEE floating point??
Condition codes?  What about the VAX vector unit?  Trap handlers, and
the stack searches for them? 

We know the page size... because they probably can't find all of the
places where VMS assumed it.
-- 
Don		D.C.Lindsay