On Fri, May 10, 2013 at 7:16 PM, Per Bothner <p...@bothner.com> wrote:
> Fail hard is probably the wrong thing to do - except when debugging. > I think what you want is the default to not fail if it can't pop > the stack frame, but that there be a VM option to throw an Error > or even do a VM abort in those case. You'd run the test suite > in this mode. > > That assumes that there is well-specified a minimal set of > circumstances in which the inlining is done correctly, > so a compiler or programmer can count on that, and that this > set is sufficient for low-overhead tail-call elimination. > Making such guarantees would have to be explicit in the JVM spec, and then we're sorta back to requiring a hard tail call guarantee (a hard inlining guarantee to ensure tail calling happens is just a horse of a different color). There is actually a way to force inlining with the newer invokedynamic impl: a @ForceInline (I forget the actual name) annotation that the LambdaForm stuff uses internally. Now, if that were exposed as a standard JVM feature, we could make such a hard guarantee...and then we're back to having to tag calls or callees with annotations, which was something you wanted to avoid (why, exactly?). > I'll be happy when I can run Kawa with --full-tailcalls > as the default with at most a minor performance degradation. > If we don't get there, I'll be satisfied if at least it is > faster (and simpler!) than the current trampoline-based > implementation. There's still a tail call patch in the MLVM repo, rotting on the vine. :-) - Charlie
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