On Mon, 13 Feb 2012, Richard Guenther wrote: > Indeed. But note that the transform is not valid as *this_node may cross > a page boundary and thus either pointer load may trap if the other does not > (well, unless the C standard (and thus our middle-end) would require that > iff ptr->component does not trap that *ptr does not trap either - we would > require a operand_equal_p (get_base_address ()) for both addresses). > > Joseph, can you clarify what the C standard specifies here?
The question of what the relevant objects for an access are isn't well-defined in general, but it seems doubtful that accessing via a structure type is valid if the whole structure isn't in accessible memory. (Whereas you can't speculatively load from x[1] just because x[0] was accessed - x might point to an array of size 1. And of course this applies with flexible array members - access to any bit of the structure means the part before the flexible array member is available, but the flexible array member may not extend beyond the part accessed.) -- Joseph S. Myers jos...@codesourcery.com
