> I am not very good at reasoning about reverse storage order stuff but > can it ever happen that this reverse is not the same as racc->reverse? > > In order for that to happen, we'd have to have an assignment (folded > memcpy?) between two aggregates in the original code that, at the same > offset within the aggregates, have single field structures with > different storage orders. If that has undefined behavior (even for > folded memcpy), I guess I am fine with the patch (but I cannot approve > it). If not, I'd add a condition that racc->reverse is the same as > TYPE_REVERSE_STORAGE_ORDER(lacc->type) to the if guarding all of this.
You cannot do an assignment between aggregates with opposite storage order, that's rejected by the compiler (both in C and Ada); generally speaking, such types are not compatible, even if they have the same underlying structure. We also block SRA when there is a VIEW_CONVERT_EXPR messing with the storage order, see calls to storage_order_barrier_p. And folding a memcpy between them should be invalid too (see e.g. the ongoing discussion with Richard in an earlier thread). So my understanding is that you don't need the condition. -- Eric Botcazou
