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From: jim@tiamat.fsc.com (Jim O'Connor)
Newsgroups: comp.sys.hp
Subject: Re: C Compiler Optimizer
Keywords: Optimizer C Complier
Message-ID: <766@tiamat.fsc.com>
Date: 28 Aug 90 13:06:07 GMT
References: <59169@bbn.BBN.COM>
Organization: Ahlstrom Filtration - Chattanooga,TN
Lines: 46

In article <59169@bbn.BBN.COM>, ahill@bbn.com (Alan R. Hill) writes:
> 
> 	We have experienced problems of varying symptoms while using
> the optimizer switch of the HP-UX 7.0 C compiler.  Rather than 
> extensively analyzing these problems we have opted to compile without
> optimizing.  Has anyone else noticed bad behavior with the optimizer?
> 

Yes, we have, too.  One example that comes to mind is:
(this is simplified, the actual program we used was much longer)

example.c
------
main()
{

printf("hello, world\n");

}

$ cc -o example example.c
$ example
hello, world
$ echo $?
0

$ cc -O -o example example.c
$ example
hello, world
$ echo $?
seemingly random numbers, but not once 0

I didn't really worry about this, telling myself that not using "exit(0)"
at the "normal" exit point of the program was probably bad programming
practice.  Using the optimizer also helped to point out another bad
habit of mine (learned while programming on Xenix) which is not correctly
initializing automatic variables.  In one case we had, with the optimizer
off, the automotic variable was being initialized (i.e. set to 0), but then
when we did the "production" compile and test, the program didn't work
because the variable wasn't initialized.  Like the other one, it wasn't
really the compilers fault, but I wish there was more info on what the
optimizer will do so I won't get suprised on things like this.

------------- 
James B. O'Connor			jim@tiamat.fsc.com
Ahlstrom Filtration, Inc.		615/821-4022 x. 651