Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!uflorida!travis!tom From: tom@ssd.csd.harris.com (Tom Horsley) Newsgroups: comp.sys.m88k Subject: Re: Machines that use the 88's Message-ID: Date: 12 Apr 91 11:08:55 GMT References: <28747@dime.cs.umass.edu> <676@adpplz.UUCP> <5@metran.UUCP> Sender: news@travis.csd.harris.com Distribution: na Organization: Harris Computer Systems Division Lines: 37 In-reply-to: meissner@osf.org's message of 11 Apr 91 22:38:44 GMT meissner> * Standard doesn't include a small data area, which allows one meissner> instruction memory references to small static/global items. meissner> It was in at one time, and then removed. But the standard does include 4 reserved registers for the linker to use as it sees fit. Our (Harris Computer Systems Division) compiler tools include a post-linker optimizer that uses these 4 registers to hold the 4 most common values appearing in 'or.u' instructions, and then squeezes out the or.u instructions. Statistics we have gathered on a very wide range of programs show that we almost always get the majority of the memory references this way (some fortran programs with heavy common block usage speed up by 15-20%). In fact, for most programs, using only 2 base registers (rather than the 4 available) covers most of the memory references. A "small data" area would require an omniscient compiler that could predict ahead of time how much data any given compilation unit could be allowed to allocate to the small data area so that it doesn't overflow once the program is linked with all the other compilation units that allocate small data space. If you overflow the small data area, you then have to go back and recompile something. meissner> * Passing structures on the stack. This makes varargs real meissner> awkward. Yep. This is the stupidest bonehead idea in the whole OCS standard, but note that it doesn't have anything to do with the hardware architecture (of course we are still stuck with it if we want to be standard conforming). -- ====================================================================== domain: tahorsley@csd.harris.com USMail: Tom Horsley uucp: ...!uunet!hcx1!tahorsley 511 Kingbird Circle Delray Beach, FL 33444 +==== Censorship is the only form of Obscenity ======================+ | (Wait, I forgot government tobacco subsidies...) | +====================================================================+