Path: utzoo!attcan!uunet!portal!cup.portal.com!bcase
From: bcase@cup.portal.com (Brian bcase Case)
Newsgroups: comp.arch
Subject: Re: object <-> object translation (was Re: VLIW)
Message-ID: <11560@cup.portal.com>
Date: 20 Nov 88 20:50:48 GMT
References: <3386@pt.cs.cmu.edu> <74435@sun.uucp> <70@armada.UUCP> <550@m3.mfci.UUCP> <2152@ficc.uu.net> <552@m3.mfci.UUCP> <76500@sun.uucp> <10643@tekecs.TEK.COM> <8523@wright.mips.COM>
Organization: The Portal System (TM)
Lines: 37

WRT to object-object compilation:
>MIPS has done it twice, once translating MIPS code to VAX code (in the
>early days before MIPS hardware) and once translating MIPS code to
>MIPS code (used for profiling (shipped as part of the compiler
>suite)).  The hardest part is dealing with the environment, even when
>translating from MIPS->MIPS!

Earl, you translated MIPS *binary* code to VAX and MIPS *binary* code
to MIPS?  I thought it was MIPS assembly code....

How did you deal with the jump tables associated with switch statements?
What strategy did you use for other indirect branches (e.g., returns)?

>By the way, MIPS machine code is particularly easy to translate to
>other machine code because the instructions are fixed size (fairly
>common these days) and tend to be single-purpose, i.e. not lots of
>useless side effects (still uncommon today).

Yeah, but try it for a 68K or VAX or 386.  It is hard to tell code from
data.

I have "done" object-object code translation three times now (actually
built two monsters and spec'd a third).  The easiest is when a RISC is
the source: at least then you can compile areas of the object image that
look like data but might be code in a reliable way:  if you translate
some data as code, you've only done extra work and increased the size
of the image on disk, but at least it's bullet-proof.

WRT to comments made about the Phoenix and Insignia Solutions' "solutions"
to this problem:  they are interpreters, perhaps incrementally-compiling
interpreters, but interpreters nontheless.  The Hunter Systems' approach
is the only true, static compiler of which I know.  At last the count,
the Insignia solutions ran applications in close to real time on a SUN-3
if you consider PC-XT speed real time (they might have improved this
significantly since I last saw a demo).  Hunter Systems' stuff runs at
something like 80386 speed on a SUN-3.  Of course, the Hunter Systems'
stuff requires some up-front, human labor to create key files.