On 01/30/2013 03:51 PM, Richard Biener wrote: > On Wed, Jan 30, 2013 at 4:49 PM, Andrew Haley <a...@redhat.com> wrote: >> On 01/30/2013 03:46 PM, Richard Biener wrote: >>> On Wed, Jan 30, 2013 at 3:22 PM, Andrew Haley <a...@redhat.com> wrote: >>>> >>>> The problem is that LLVM assumes that values are extended at a call. GCC >>>> does that, but libffi doesn't. So, calls via libffi to LLVM don't work >>>> correctly. >>> >>> It's an optimization to do so to avoid partial register stalls. >> >> Well, it's hardly an optimization if it's incorrect, and it seems to be >> incorrect. As the old saying goes, I can make your code infinitely fast >> if you don't care about the results. > > It's incorrect to rely on the extension taking place. It's not incorrect to > do the extension.
Sure, I understand that, but I am completely baffled as to how extending at a call site avoids partial register stalls if a callee cannot assume that a value is already extended. Andrew.
