majnemer added a subscriber: majnemer. majnemer added a comment. In http://reviews.llvm.org/D12052#225194, @mkuper wrote:
> Thanks, Simon! > I've wanted to add the _undefined intrinsics for a while now, but never got > to it. > > Anyway, this sort of implementation somewhat worries me. > Yes, I know that the gcc intrinsics do something very similar. > And I also know that in practice we'll get an undef value, nothing worse > (assuming reading an uninitialized automatic variable is undefined behavior > to begin with - which really depends on the spec interpretation :-) ). > And I know this isn't likely to change anytime soon. > > Still, relying on what may be undefined behavior in the header files worries > me, and I'd rather not have it implemented like that. > I was thinking about adding a __builtin_undef which explicitly resolves to > an undef value. > Does that make sense to you? `__builtin_undef` seems like a pretty big hammer and does not sound trivial to implement. Not all types that can be emitted have an `undef` representation. For example, `x86_mmx` doesn't have an `undef` representation because there can be no constants of that type. I'd recommend a more narrow implementation technique unless we really need a more general one. Repository: rL LLVM http://reviews.llvm.org/D12052 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
