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From: wunder@hp-ses.SDE.HP.COM (Walter Underwood)
Newsgroups: comp.sys.hp
Subject: Re: C Compiler Optimizer
Message-ID: <920067@hp-ses.SDE.HP.COM>
Date: 29 Aug 90 18:39:30 GMT
References: <59169@bbn.BBN.COM>
Organization: HP SW Engineering Systems - Sunnyvale, CA
Lines: 38


   example.c
   ------
   main()
   {
   printf("hello, world\n");
   }

Exiting with an unpredictable number is proper behavior for this 
program.  It is not a defect.  Notice:

   $ lint /tmp/example.c

   example.c
   ==============
   (6)  warning: main() returns random value to invocation environment

   ...

Which is exactly what your code does when optimized.  The repeatable
behavior when not optimized is due to luck, not C.  Here is a fixed
version of "example.c".

   int main()
   {
   printf("hello, world\n");
   return 0;
   }

Now, the main() routine returns a type which matches its declared
return type.  This is correct C.

When program behavior changes under optimization, use lint to find out
whether the code depends on things that C doesn't guarantee.  You can
also use C++, which has much more strict checking and just won't
compile code with type mismatches.

wunder