Robert Dewar <dewar <at> adacore.com> writes: > In any case the gcc interpretation is clearly what's > intended in my view, so if it can be argued that the > standard is inconsistent with this interpretation (I > am unconvinced that this burden has been met), then > the conclusion is to add a clarification to the > standard, not to modify the gcc behavior.
I agree with you completely on this point. My position throughout this thread has been that GCC should keep its existing type-based aliasing behavior. I think the GCC policy represents a good trade-off between a policy that is not aggressive enough and a policy that is too hard to follow. In my view the C99 standard quite clearly specifies a policy that is less aggressive than what GCC implements. I think it's hard to come to any other conclusion; section 6.5 paragraph 7 contains a footnote explicitly stating that the intention is to specify conditions under which values may be aliased, and one of the rules allows for an aliasing condition that GCC does not respect. I have not heard any credible rebuttal to this point, or any explanation of what 6.5 paragraph 7 *does* mean, if it is not intended to specify aliasing rules. I am guessing that the committee didn't have enough practical experience with aliasing policies to come to Richard's conclusion that the standard's policy "removes nearly all advantages of type-based aliasing that you have when dealing with disambiguating a pointer dereference vs. an object reference." In this sense I think this is a bug in the standard, and I hope the committee will take it up in C1x. Josh
