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From: piet@cs.ruu.nl (Piet van Oostrum)
Newsgroups: gnu.gcc.bug
Subject: Re: 68000 code generation
Message-ID: <1401@ruuinf.cs.ruu.nl>
Date: 23 Jun 89 15:37:42 GMT
References: <8906221536.AA26520@dvlmarv.UUCP>
Sender: piet@ruuinf.cs.ruu.nl
Reply-To: piet@cs.ruu.nl (Piet van Oostrum)
Distribution: gnu
Organization: Dept of Computer Science, University of Utrecht, Holland
Lines: 23
In-reply-to: gatech!dvlmarv!richards@EDDIE.MIT.EDU (Richard Sewards)

In article <8906221536.AA26520@dvlmarv.UUCP>, gatech!dvlmarv!richards@EDDIE (Richard Sewards) writes:
 `
 `
 `I've found a code generation bug in gcc 1.34 with the 68000 code generator.
 `The following is the assembler output (and corresponding source lines) where
 `the problem occurs and after that I'm including the entire (preprocessed)
 `source file which generates the bug with comments at the lines where the
 `problem is.
 `
 `The problems is that for register pointer variables compared with 0 a
 `word comparison is done instead of a long comparison.
 `
 `			cmpw #0,a2

This is not a bug, it is a feature. The 68000 instruction actually used is
a cmpa (compare address register). If this instruction is used with a word
operand that operand is sign-extended, and then compared with the 32-bit
address register. So it does the same as the long version, but is 2 bytes
shorter. 
-- 
Piet van Oostrum, Dept of Computer Science, University of Utrecht
Padualaan 14, P.O. Box 80.089, 3508 TB Utrecht, The Netherlands
Telephone: +31-30-531806. piet@cs.ruu.nl (mcvax!hp4nl!ruuinf!piet)