Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!microsoft!markro
From: markro@microsoft.UUCP (Mark ROBERTS)
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Re: No Aliasing Compile Option
Keywords: Microsoft 6.0 C update woes
Message-ID: <55054@microsoft.UUCP>
Date: 5 Jun 90 17:02:22 GMT
References: <1990May23.234917.21858@uunet!unhd> <250@demott.COM> <12215@bunker.UUCP>
Reply-To: markro@microsoft.UUCP (Mark ROBERTS)
Organization: Microsoft Corp., Redmond WA
Lines: 44

In article <12215@bunker.UUCP> shap@clunker.UUCP (Joseph D. Shapiro) writes:
>In file a.c
>
>	static int foo;
>
>	main()
>	{ bar(foo); }
>
>	baz()
>	{ foo++; }
>
>in file b.c
>
>	foo(int x)
>	{ ... establish a value for x here ...
>		baz();
> 	  ... reference x here ...
>	}
>
>is this not aliasing as well?
>will not -Oa cause trouble in b.c?

Well, sort of.  I think you have a couple of problems with your example -
the function foo should be named bar and since ints are passed by value 
there can be no aliasing.  But, try this:
	static int foo;

	main()
	{ bar(&foo); }

	baz()
	{ foo++; }

	int bar(int *x)
	{
		*x=3;
		baz();
		return *x;
	}

Now you've got aliasing and -Oa will fail, even in same file.  But is it
the same example?  Do people really write code like this?  I would certainly
not encourage this, but no doubt its done.  In which case, you can't use
-Oa; however, -Ow would work.