Re: OP_TAILCALL versus OP_CALL question

[Pierre-Yves Gérardy <pygy79@...>]

The trouble is that you can't do that with LLVM.

It does support TCO, though, at the expense of easy C interop (you
have to use incompatible calling conventions which breaks the ABI). As
long as you don't want to mix C and Lua/Ravi code, FFI-style, you
should be fine.

http://llvm.org/docs/CodeGenerator.html#tail-call-optimization
http://llvm.org/docs/LangRef.html#calling-conventions
—Pierre-Yves


On Sat, Mar 21, 2015 at 4:23 PM, Coda Highland <chighland@gmail.com> wrote:
> On Fri, Mar 20, 2015 at 3:25 PM, Dibyendu Majumdar
> <mobile@majumdar.org.uk> wrote:
>> On 20 March 2015 at 22:16, Doug Currie <doug.currie@gmail.com> wrote:
>>>> I haven't yet figured out how to properly implement OP_TAILCALL in a
>>>> JITed function.
>>>
>>>
>>> The usual approach is to emit code to pop the stack frame and convert the
>>> tail call to a jump.
>>>
>>
>> In the recursive case, yes, but Lua also uses tail calls for
>> non-recursive scenarios. For these a different function may be called
>> so it is not possible to handle this in a JITed function - without
>> replacing the function being executed as well.
>>
>> Regards
>>
>
> The technique still applies to the non-recursive case -- you still
> clean up the stack frame, push on the return values, and jump.
>
> /s/ Adam
>