[Bug tree-optimization/48702] [4.6/4.7 Regression] optimization regression with gcc-4.6 on x86_64-unknown-linux-gnu

[xinliangli at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48702

--- Comment #18 from davidxl <xinliangli at gmail dot com> 2011-05-17 20:40:41 UTC ---
(In reply to comment #17)
> > This is not really heuristic -- it prevents compiler from generating code in
> > ivopt that violates the aliasing assumption. 
> 
> no, it does not. 

Does, but may not fully do.

> For example, you only consider the case whent the base of the
> memory
> reference is addr_expr, and when the step is negative.  However, ivopts may
> generate
> "pointers" outside of the memory objects in other cases as well;


Those would be bugs too -- do you have such examples? 

David

> and if those
> get used in
> mem_refs (where the computations are currently interpreted according to the
> pointer
> arithmetics rules, for the purpose of alias analysis), this leads to
> misscompilations.