------- Comment #14 from mmitchel at gcc dot gnu dot org 2009-01-25 19:45 ------- Richard --
I don't agree that it's necessarily the FE's job to omit all stores to such types. Our general theory is that FEs get to emit dumb code and the optimizers get to fix it up. Of course, I don't object to making the FE generate simpler code, if that's easy to do; just that if our design relies on that, I think that's a mistake. I can imagine ways this could come up in other languages as well. For example, copying a C structure with an anonymous bit-field, but no other content, or an Ada record that uses Ada's layout directives to control size. Therefore, I don't think that the key here is "zero-size". Instead, it's the fact that structure cannot be initialized. That's useful both for warnings and for optimization; it can't be initialized, so there's no point about warning about uninitialized uses, and there's no reason to actually generate code for the copies. That leads to something I do think is something that the FEs could be asked to do: set a bit on the type to indicate that it is uninitializable or, if you like, logically empty. I also don't see this as a P1 defect. It's certainly annoying, but, fundamentally, it limits the utility of a warning which has been known to give false positives for a long time. Important to fix, yes -- but as important as generating wrong code? -- Mark -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38851
