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From: gstein@oracle.com (Greg Stein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MPW compiler bugs (was: interface war)
Message-ID: <1990Feb14.004350.14475@oracle.com>
Date: 14 Feb 90 00:43:50 GMT
Sender: news@oracle.com
Reply-To: gstein@oracle.com (Greg Stein)
Organization: Oracle Corporation, Belmont, CA
Lines: 68

> From: jln@acns.nwu.edu (John Norstad)
> In article <1046@watserv1.waterloo.edu> bmwrkshp@watserv1.waterloo.edu ( 
> Wrkshp Id - Sys Design ) writes:
> > But I'm sure THINK C is still an order of magnitude
> > faster. Don't know what that linker is doing. Sure takes its own
> > sweet time even on Mac II's.
> 
> As I understand it, one of the reasons is that MPW's linker is much 
> smarter.  For example, it lets you direct individual routines within a 
> single module to different segments, and it eliminates dead code.  I'm not 
> sure about all this, though.
> 
> > I would probably use MPW 99% of the time if it weren't for the fact
> > that the C compiler is broken. Even the updated C compiler
> > included with the C++ package still has bugs.
> 
> I've heard this from other places too (e.g., the guys at Wolfram).  But 
> I'm up to 16,000 lines of pretty hairy C code in Disinfectant now, and 
> I've yet to encounter a single compiler bug.  Maybe because I'm a reformed 
> Pascal fanatic, I don't write as ugly code as the rest of you guys :-)
> 
> John Norstad
> Northwestern University
> jln@acns.nwu.edu
> 

I have a nice bug from V3.1b3e19 of MPW C.  Type in this little code
fragment, compile it, and look at its output:

int main()
{
    char *a, *b = 0L;
    int c = 0L;		/* assignment to prevent warnings */

    if (a = &b[c])
	return(1);
    return(2);
}

The relevant part is this:

    ...
    LEA   $00(A3,D7.L),A4	; all vars are in registers
    BEQ.S @1
    ...

Note that a conditional branch is performed without any testing being
done.  (Yes, the bug has been reported to Apple)  Don't ask me how I
found the bug, but it is repeatable.

Things like this make me wonder just how stable the compiler is.  I
realize that I have a Beta version and that the line of code above is
sheer idiocy for most purposes, but still...

John, I will agree with you, though, about the Linker.  Think C
includes code a whole file at a time -- it won't pick out individual
routines from a file.  MPW C will do this.  What I don't get is why
Think C hasn't changed this by now -- they've had a few versions to do
it.  Heck, in high school when I wrote the Rascal compiler for the
Mac, I wrote a linker that did dead code analysis and picked out a
routine at a time.  Surely, Mike Kahl could do it.

Well, John, I don't know whether you write ugly code or not, but
Disinfectant 1.6 is a very nice piece of work.  Thanx.

Greg Stein	-- This posting bears no relation to my employer
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