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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix-wizards
Subject: Re: Sun C compiler bug
Message-ID: <1012@umcp-cs.UUCP>
Date: Fri, 26-Jul-85 14:12:52 EDT
Article-I.D.: umcp-cs.1012
Posted: Fri Jul 26 14:12:52 1985
Date-Received: Sun, 28-Jul-85 03:25:08 EDT
References: <666@cvl.UUCP>
Distribution: net
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 37

Speaking of Sun C compiler bugs, how about

	struct bug {
		struct { int field:4; } array[128];
	};

	f()
	{
		register struct bug *p;
		register int i;

		p->array[i].field;
	}

which generates

	movl	d7,d0
	asll	#1,d0
	moveq	#0,d0			; sorry, guys, ya blew it
	movb	a5@(0,d0:l),d0
	lsrl	#4,d0
	andb	#0xf,d0

The code is just fine except for the minor fact that it is using
the same temp for both the subscript operation and the dereference.
Makes all references to "register pointer to array of bitfield"
access the 0th element, always.  (The problem doesn't occur with
arrays of anything else, nor with pointers to bitfields.)

Without the compiler sources, of course, I can't provide a fix
(hint hint :-) ).  Note however that the problem goes away if one
simply does not clear the destination of a move for a FLD reference,
since the result will be masked anyway....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@maryland