Path: utzoo!utgpu!water!watmath!clyde!bellcore!decvax!ucbvax!agate!ig!uwmcsd1!bbn!husc6!linus!philabs!pwa-b!mmintl!franka
From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: comp.arch
Subject: Re: RISC data alignment
Message-ID: <2710@mmintl.UUCP>
Date: 9 Feb 88 14:34:51 GMT
References: <2635@calmasd.GE.COM> <28200092@ccvaxa>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Organization: Multimate International, E. Hartford, CT.
Lines: 19

In article <28200092@ccvaxa> aglew@ccvaxa.UUCP (Andy "Krazy" Glew) writes:
>I have often wanted an optimizing compiler that could take
>struct { long a; int b; long c; char d; }
>which is usually mapped into bytes as AAAABBxxCCCCDxxx
>(on a machine where misaligned accesses are penalized)
>and make it into AAAACCCCBBDx.

How about AAAABBDxCCCC?  This is what results if you follow the rule "put
each component into the first suitable place for it".  It has the important
property that structures with the first few components identically defined
will have those components in the same place.  This is important -- the C++
translator relies on it, for example.

Code that includes a size 1 (or size 0) array at the end of a structure to
represent a variable-sized array may still be broken, however.
-- 

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Ashton-Tate          52 Oakland Ave North         E. Hartford, CT 06108