Path: utzoo!attcan!uunet!mcvax!ukc!dcl-cs!aber-cs!pcg
From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.arch
Subject: Re: Register usage [was Re: 80486 vs. 68040 code size]
Summary: PCC used a fine register allocator. The test was with many regs.
Message-ID: <949@aber-cs.UUCP>
Date: 15 May 89 17:00:56 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Distribution: eunet,world
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 19

In article <1989May11.210653.2125@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
     
    You forgot one condition:  ancient and stupid compiler.  Do remember, also,
    that most any compiler for the 11 was full of implicit assumptions to the
    effect that very few registers were available.

Now I may be totally wrong, but I seem to remember that they used PCC and tuned
its (bastardized) Sethi Ullman register allocator, which is both pretty
good (even the [S]CC one was quite good) and with no assumptions at all.

They were as surprised as anybody at their results, and the obvious
conclusion was the simple "most C expression are very simple, even those in
critical paths". (my memory supplies me with something like: 80% of all
C expressions have less than two operators, and about half have just one,
on the usual sample of UNIX/C code).
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk