On 11/06/2014 06:45 PM, Ian Taylor wrote: > On Thu, Nov 6, 2014 at 5:04 AM, Richard Henderson <r...@redhat.com> wrote: >> >> That said, this *may* not actually be a problem. It's not the direct >> (possibly >> lazy bound) call into libffi that needs a static chain, it's the indirect >> call >> that libffi produces. And the indirect calls that Go produces. >> >> I'm pretty sure that there are no dynamically linked Go calls that require >> the >> static chain. They're used for closures, which are either fully indirect >> from >> a different translation unit, or locally bound closures through which the >> optimizer has seen the construction, and optimized to a direct call. >> >> Ian, have I missed a case where a closure could wind up with a direct call >> to a >> lazy bound function? > > I think you've covered all the cases. The closure value is only > required when calling a nested function. There is no way to refer > directly to a nested function defined in a different shared library. > The only way you can get such a reference is if some function in that > shared library returns it.
Sorry, I wasn't clear. I know nested functions must be local. I'm asking about Go closures, supposing we go ahead with the change to make them use the static chain register. I'm merely pretty sure that calling a closure is either fully indirect or local direct. Certainly there are cases in the testsuite where -O3 is able to look through the creation of a closure and have a direct call to the function. Given that closures are custom created for the data at the creation site, it seems unlikely that the optimizer could look through that and come up with a dynamically bound function. r~
