Re: LuaJIT - Trace aborted again

[Benjamin Segovia <segovia.benjamin@...>]

Also, Robert, I will try your suggestion :-)
I hope it will work ie replacing my hack (nested double loop) by the
(function() ... end)() hack. Using a function for each loop body, I
can replace breaks / continues by returns and remove one repeat ...
until crap.
I hope it will do the job :-)
Otherwise, I will try to go through if/then/else code transform hell...
So, also thanks for the suggestion :-)

Ben


On Wed, Jul 20, 2011 at 4:45 PM, Benjamin Segovia
<segovia.benjamin@gmail.com> wrote:
> Hmmm.
> This is not really a if/then/else construct I need but really a
> forward jump. Basically, it is a SIMD scatter/gather machine. Some
> instructions inactivate lanes from the SIMD vector. In a block, if
> your instruction currently deactivates all lanes, then you exit the
> block, reset the mask you got before potentially modified by the
> computations in the previous block. Then you check the current mask.
> If it is still zero, then you exit the block ...
>
> Maybe to be more precise: the biggest issue basically is that I need
> to emulate "continue" and "breaks" because the machine can execute
> "continue" and "break" instructions natively.
> Actually "continue" instructions are really the big problem, since
> there is no continue in lua.
>
> Right now, I used a two-nested-loop hack to handle continue:
>
> repeat
> local a_break_was_used_for_a_continue = false
> repeat
>
> -- .... "CONTINUE"  instruction generates ->
> a_break_was_used_for_a_continue = true
> break
> -- end of continue
>
> -- .... "BREAK" instruction generates ->
> a_break_was_used_for_a_continue = false
> break
> -- end of break
>
> until true -- <- this is fake loop to early branch out (used for
> breaks and continues)
> if not a_break_was_used_for_a_continue then beak end
> until false -- <- this is a real loop. Youhou!
>
> As you can see, the technique is easy to implement since regardless
> where I am in the nested branches (like for example, deeply nested in
> IFs), I can early out.
> I am afraid that using only if/then/else to mask the code may be a
> more serious code transform. Something similar to unstructured
> branches to structures branches transform... ie not that easy to do
> :-)
>
> I will try other things today.
>
> Thank you very much for your help
>
> Ben
>
>
>
> On Wed, Jul 20, 2011 at 2:52 PM, Mike Pall <mikelu-1107@mike.de> wrote:
>> David Kastrup wrote:
>>> Mike Pall <mikelu-1107@mike.de> writes:
>>> > I do not see how that's different from doing it with a while loop.
>>> > You'd need to nest them and close them with 'end' as well.
>>>
>>> No, you need just a single loop at a time that can deal with dozens of
>>> "break" in there.
>>
>> Sure. But is that a realistic use case? If the VLIW code is
>> generated from typical code in a high-level language, I doubt
>> you'd see more than a handful of these. Nesting (say) 100
>> if/then/else is no problem.
>>
>> --Mike
>>
>>
>