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From: hrubin@osupyr.UUCP (Herman Rubin)
Newsgroups: comp.arch
Subject: Re: Optimizing compiler's view on: no. of regs, aliasing, caller/callee save etc.
Message-ID: <85@osupyr.UUCP>
Date: Mon, 9-Mar-87 15:56:36 EST
Article-I.D.: osupyr.85
Posted: Mon Mar  9 15:56:36 1987
Date-Received: Wed, 11-Mar-87 04:42:13 EST
References: <902@orcisi.UUCP> <1283@ucbcad.berkeley.edu> <4277@utcsri.UUCP>
Organization: Department of Statistics
Lines: 18
Summary: Keeping track of registers is not so expensive in hardware

It is not that difficult for hardware to avoid register loss in subroutine
calls while minimizing register saving.  The callee saves those registers
which the caller tells it are in use and which the callee needs, and keeps
a bit pattern of those the caller sends which it does not use.  It would
then send this list or-ed with the list of its active registers when it
makes another call.  Thus it is not merely building up a long list by or's.
Having written programs with unavoidable rare conditional subroutine calls,
I can unequivocally state that having the caller save registers can be so
costly as to require kludges.
-- 
Herman Rubin
Until mid May:
Department of Statistics, Cockins Hall, 1958 Neil Avenue
Ohio State University, Columbus OH43210
hrubin@osupyr or cbosgd!osu-eddie!osupyr!hrubin or ts0474@ohstvma.bitnet
"Permanent":
Department of Statistics, Purdue University, West Lafayette IN47907
hrubin@l.cc.purdue.edu or ihnp4!pur-ee!stat-l!hrubin or hrubin@purccvm.bitnet