Path: utzoo!attcan!uunet!husc6!think!ames!oliveb!sun!gorodish!guy
From: guy@gorodish.Sun.COM (Guy Harris)
Newsgroups: comp.arch
Subject: Re: Self-modifying code
Message-ID: <61269@sun.uucp>
Date: 25 Jul 88 19:00:24 GMT
References: <6341@bloom-beacon.MIT.EDU> <60859@sun.uucp> <474@m3.mfci.UUCP>
Sender: news@sun.uucp
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> You are asking for way too much, Guy.  Computer system designers
> can't even agree on performance metrics, and performance is probably
> the easiest thing to measure about a computer system (as compared to,
> say, reliability or programmer productivity).

Well, I don't necessarily want numbers complete with reliable error bars; I'd
be interested just to hear anecdotal stories such as "it took this team 10
times as long to do this project under XYZZY's Ada on a PC as it did for some
other team to do it on FFGGF's Ada on the FFGGF
Ada-Interpreter-In-Microcode(TM) processor", as long as the two teams were of
comparable quality.

> But my intuition is also that, for the same reasons that we
> instinctively reach for the best tools for the job at hand (C,
> assembly, Lisp, Ada, etc.), we would do considerably better as
> programmers if the "thing" (including architecture, language, & OS)
> executing our code matched our expectations as closely as possible,
> and with few surprises.

Yes, but is there any indication of whether we'd do better by changing the
architecture (meaning the instruction-set architecture) or by changing the
compiler, holding other things pretty much equal (e.g., the language)?

> And further, if it made sure we knew the nature of whatever surprises
> occurred, rather than (a C example) having an array-pointer-out-of-bounds
> happen to trash a scalar value that was coincidentally declared nearby.
> I don't see higher performance as a very good means of preventing errors
> like that.

If the performance is enough greater, you could spend some of the performance
gain by inserting instructions to do run-time array bounds checks.  If the
compiler is good enough to optimize away most of those checks, you may spend
less than you might expect to.