Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!ames!amdcad!amd!intelca!mipos3!omepd!mcg
From: mcg@omepd.UUCP
Newsgroups: comp.lang.c
Subject: Re: Porting PCC
Message-ID: <801@omepd>
Date: Wed, 17-Jun-87 00:18:48 EDT
Article-I.D.: omepd.801
Posted: Wed Jun 17 00:18:48 1987
Date-Received: Fri, 19-Jun-87 01:13:05 EDT
References: <2082@dg_rtp.UUCP> <5975@brl-smoke.ARPA> <6604@ism780c.UUCP> <21214@sun.uucp>
Reply-To: mcg@omepd.UUCP (Steven McGeady)
Organization: Intel Corp., Hillsboro
Lines: 24
Summary: QCC ~= RCC


QCC and RCC are almost the same thing.  They differ in the exact algorithm
used for instruction selection.  RCC does a complex (and time-expensive)
cost comparison among certain alternatives.  QCC operates on an
ordered list of alternatives, and simply picks the first one that applies.
The only files that would differ between the two versions are scommon/cost.c
and scommon/match.c.

The belief is that this generates the best code most of the time, and
is substantially faster in compiler speed.  QCC is the 'Quick RCC'.
I believe that the version on 3B's is actually QCC - RCC is a research tool.

V.3 also includes an optimizer which, while not any better than c2,
appears to be easier to retarget ('port' is really the wrong word
for re-doing compiler backends).

What V.3 *still* does not have, and would do the reputation of PCC-based
compilers a world of good, is a (mostly) machine-independent
intermediate code optimizer (between the first and second passes)
doing things like strength reduction, dead variable elimination, etc.
This would destroy the one-pass ("filter") aspect of PCC, but would
generate substantially better code.

S. McGeady