Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!husc6!mailrus!umix!uunet!steinmetz!sunset!oconnor
From: oconnor@sunset.steinmetz (Dennis M. O'Connor)
Newsgroups: comp.arch
Subject: Re: condition codes
Message-ID: <9630@steinmetz.steinmetz.UUCP>
Date: 20 Feb 88 15:50:08 GMT
References: <4252@aw.sei.cmu.edu>
Sender: news@steinmetz.steinmetz.UUCP
Reply-To: sunset!oconnor@steinmetz.UUCP
Organization: GE Corporate R&D Center
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IMHO, there is still one and only one good reason for
including condition codes in an architecture :

Translation of code from or emulation of an existing architecture
that already has them.

There's just no good way to do it unless you have a "compatable"
set of condition codes.

What I like is a "condition" or "skip" instruction, that
can cause the following instruction to NOT be executed
if the test fails. This means you need to have the result
of the test ready in one instruction-interval, which
can indeed cause a new critical path. But it's clean,
and lets you eliminate branches by "conditionalizing"
other types of instructions. Since the "CONDITION" instruction
is an entire instruction, you get lots of flexibility in what's being
tested and what's being tested for.

And yes, if you want to, you can test the bits in the condition-code
register, if you've got one. :-)
--
	Dennis O'Connor 	oconnor@sunset.steinmetz.UUCP ??
				ARPA: OCONNORDM@ge-crd.arpa
    "Nuclear War is NOT the worst thing people can do to this planet."