Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!gatech!hao!husc6!mit-eddie!uw-beaver!tektronix!cae780!amdcad!amd!intelca!mipos3!omepd!mcg
From: mcg@omepd (Steven McGeady)
Newsgroups: comp.lang.c
Subject: Re: Porting PCC
Message-ID: <826@omepd>
Date: Thu, 18-Jun-87 14:02:47 EDT
Article-I.D.: omepd.826
Posted: Thu Jun 18 14:02:47 1987
Date-Received: Mon, 22-Jun-87 01:43:16 EDT
References: <2082@dg_rtp.UUCP> <5975@brl-smoke.ARPA> <6604@ism780c.UUCP> <21214@sun.uucp> <801@omepd> <2663@ulysses.homer.nj.att.com>
Reply-To: mcg@omepd.UUCP (Steven McGeady)
Organization: Intel Corp., Hillsboro
Lines: 49
Summary: PCC -> PCC2 -> QCC -> RCC

In article <> (Jerry Schwarz) writes:
>In article <801@omepd> mcg@omepd.UUCP (Steven McGeady) writes:
>>
>>QCC and RCC are almost the same thing. ...
>>
>McGeady is confusing rcc with pcc2.  Pcc2 was the version that
>did the code selection based on costs. The "r" in rcc stands for 
>"register".  
>
>Jerry Schwarz
>Former member of AT&T UNIX Language Department


Mr. Schwarz is correct.  My confusion resulted from seeing only the end
product, not the genealogy.  The correct story is, to quote from an AT&TIS
memo (dated June 30, 1985, by David M. Kristol):

	"PCC2, a successor to the Portable C Compiler (PCC), has
	 itself spawned two successors, QCC and RCC.  QCC is a compiler
	 technology that has the favorable maintainability properties
	 of PCC2, along with faster compilation speed than PCC or PCC2.
	 RCC, in turn, is a derivative of QCC that can deal with irregular
	 architectures through the definition of *register sets*.

	 To create a RCC compiler from a PCC2 compiler, it is easiest
	 to go through the intermediate stage of a QCC.  The steps
	 are simple, and it is not necessary to get a working QCC, in
	 the sense that it compiles all available C code ..."

To give more background, the memo "Speeding up the Portable C Compiler",
by David M. Kristol and R.B. Murray, dated February 8, 1985 (and a
Bell Labs memo, rather than AT&T IS) says:

	"PCC2 is an evolutionary outgrowth of PCC, the fundamental
	 difference being the matching algorithm.  Since the leaves of
	 the tree correspond to its shapes, PCC begins code generation
	 one level above the leaves.  At each step PCC uses the first
	 template it finds for which the OP and shapes in the template
	 match the tree....

	 PCC2 uses a dynamic programming algorithm to choose the
	 *best set* of templates that represents the semantics of
	 the tree, where *best* is based on a cost measure.  The compiler
	 writer supplies costs for templates and shapes.  The compiler
	 effectively does an exhaustive search over all possible
	 code generations for a given expression before choosing the
	 cheapest."

S. McGeady