Re: [PATCH] Fix PR26763, pointer overflow

[Richard Guenther <rguenther at suse dot de>]

On Mon, 3 Apr 2006, Richard Guenther wrote:

> 
> This patch addresses PR26763 which is another case where we end up
> with an expression relying on pointer overflow being defined.  I have
> convinced myself that it is a bad idea to assume anything about pointer
> overflow, so the only thing we can safely fold is equality and inequality.
> 
> Another possibility would be to split the cases of ADDR_EXPR 
> (ARRAY_REF(..)) from the cases that only look like these again and rely
> on the array domain for folding.  (This also hints at possible problems
> with the mem-refs as array-ref thing)
> 
> Can anyone specify the conditions in where we are allowed to do
> &a[i] CMP &a[j]  ->  i CMP j  conversion and in which cases
> a +- i CMP a +- j  ->  i CMP j  ?  (note that i and j are pointers
> in the latter case and the addition/subtraction is either signed or
> unsigned dependent on the signedness of pointers)
> 
> So, as a stop-gap for now, ok for mainline?  (I'll make sure to XFAIL
> valid transformations we no longer perform in the testcases that are
> around there)

There are no additional failures with this patch.  Bootstrapped and
regtested on x86_64-unknown-linux-gnu.

Richard.