From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joe Buck <jbuck@synopsys.COM>
To: mark@codesourcery.com (Mark Mitchell)
Cc: jbuck@synopsys.com, gcc@gcc.gnu.org, rms@gnu.org
Subject: Re: type based aliasing again
Date: Wed, 08 Sep 1999 21:33:00 -0000
Message-id: <199909090430.VAA24607@atrus.synopsys.com>
References: <19990908202957F.mitchell@codesourcery.com>
X-SW-Source: 1999-09/msg00330.html

One more thought:

[ C means that we declare an error if we detect illegal aliasing ]

Mark writes:
> I agree that C is reasonable.  But, it is not technically viable at
> compile-time; the violation of the rule is a dynamic property.  For
> example, consider:
> 
>   if (0) {
>     /* Do illegal aliasing stuff.  */
>   }
> 
> If we do dead-code elimination late, we might ask questions about the
> aliasing in the conditional code.  Since that code never executes,
> ANSI says there's no violation.

Careful.  Are you sure that ANSI says that we can't call this an error?
Is the language describing the type rules for accesses distinct from
other language like

	const int foo = 3;
	if (0) {
		foo = 4;
	}

?  It's illegal to assign to a const, but here we are not assigning to
a const, because the code is unreachable.



From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joe Buck <jbuck@synopsys.COM>
To: mark@codesourcery.com (Mark Mitchell)
Cc: jbuck@synopsys.com, gcc@gcc.gnu.org, rms@gnu.org
Subject: Re: type based aliasing again
Date: Thu, 30 Sep 1999 18:02:00 -0000
Message-ID: <199909090430.VAA24607@atrus.synopsys.com>
References: <19990908202957F.mitchell@codesourcery.com>
X-SW-Source: 1999-09n/msg00330.html
Message-ID: <19990930180200.AaU7WcsYFlxzxsEL1ZWk3j7Zk8I3yhAo_Y9uCB3V8bM@z>

One more thought:

[ C means that we declare an error if we detect illegal aliasing ]

Mark writes:
> I agree that C is reasonable.  But, it is not technically viable at
> compile-time; the violation of the rule is a dynamic property.  For
> example, consider:
> 
>   if (0) {
>     /* Do illegal aliasing stuff.  */
>   }
> 
> If we do dead-code elimination late, we might ask questions about the
> aliasing in the conditional code.  Since that code never executes,
> ANSI says there's no violation.

Careful.  Are you sure that ANSI says that we can't call this an error?
Is the language describing the type rules for accesses distinct from
other language like

	const int foo = 3;
	if (0) {
		foo = 4;
	}

?  It's illegal to assign to a const, but here we are not assigning to
a const, because the code is unreachable.