Re: middle-end/9725: Invalid dependency determination

[Wolfgang Bangerth <bangerth@ticam.utexas.edu>]

The following reply was made to PR middle-end/9725; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
To: Jan Beulich <JBeulich@novell.com>
Cc: gcc-bugs@gcc.gnu.org, <gcc-gnats@gcc.gnu.org>
Subject: Re: middle-end/9725: Invalid dependency determination
Date: Mon, 17 Feb 2003 10:49:29 -0600 (CST)

 > I was fearing you would say this. But I can in no way agree - the code
 > presented is valid C, and hence should work at any optimization level.
 
 What makes you think so? gcc's info pages show
 
 `-fstrict-aliasing'
      Allows the compiler to assume the strictest aliasing rules
      applicable to the language being compiled.  For C (and C++), this
      activates optimizations based on the type of expressions.  In
      particular, an object of one type is assumed never to reside at
      the same address as an object of a different type, unless the
      types are almost the same.  For example, an `unsigned int' can
      alias an `int', but not a `void*' or a `double'.  A character type
      may alias any other type.
 
 In your code you try to pretend that a variable of type "struct S" resides 
 at the place of a long long. That's exactly the case that's covered above, 
 which in turn exactly parallels what the standard says.
 
 W.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth             email:            bangerth@ticam.utexas.edu
                               www: http://www.ticam.utexas.edu/~bangerth/