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...ide a callee... we see a pointer returned from the callee, but don't know what its value is. alias analysis says that a MayAlias b, unless the callee's return value is marked noalias, in which case alias analysis says that a NoAlias b. With either of these results, the invariance on a->vtblptr is not applied to any loads of b->vtblptr. It is, however, applied to loads a->vtblptr, which is exactly what we want. And the reverse is true for any invariance applied to b->vtblptr. If the callee is ever inlined, we're back to case 1. So now we need a way to arrange for pointers...

On Oct 13, 2010, at 5:09 PM, Kenneth Uildriks wrote: > But I believe the language does allow "undefined behavior" if there's > a use of pT when the pointed-to object isn't actually of type T. It's > an invalid use in that case, right? Yes, but not for an arbitrary pointer which aliases pT. That's why it's a problem that llm.invariant is specified in terms

On Wed, Oct 13, 2010 at 6:49 PM, John McCall <rjmccall at apple.com> wrote: > > On Oct 13, 2010, at 4:35 AM, Kenneth Uildriks wrote: > >> On Wed, Oct 13, 2010 at 12:45 AM, Nick Lewycky <nicholas at mxc.ca> wrote: >>> Kenneth Uildriks wrote: >>>>> >>>>> You're right, I hadn't thought this through. The whole point of making