Path: utzoo!attcan!uunet!tektronix!orca!frip!andrew
From: andrew@frip.WV.TEK.COM (Andrew Klossner)
Newsgroups: comp.arch
Subject: Re: Register usage
Message-ID: <3354@orca.WV.TEK.COM>
Date: 17 May 89 20:06:38 GMT
References: <921@aber-cs.UUCP> <16052@bellcore.bellcore.com>
Sender: nobody@orca.WV.TEK.COM
Distribution: eunet,world
Organization: Tektronix, Wilsonville, Oregon
Lines: 21

[]

	"Larger register sets pay you back when you do dataflow
	analysis and allocate registers over larger spans of code than
	C expression statements ... If you only have a handful of
	registers, though, you might as well keep it simple."

Dataflow analysis is good for more than register allocation, and can be
a win on a register-starved machine.  For example, when compiling this
code (which swaps "x" and "y"):

	temp := x;
	x := y;
	y := temp;

if dataflow analysis tells you that "temp" is dead after this fragment,
you can avoid a store operation, and you've won even if you have only
two registers.

  -=- Andrew Klossner   (uunet!tektronix!orca!frip!andrew)      [UUCP]
                        (andrew%frip.wv.tek.com@relay.cs.net)   [ARPA]