Re: LuaJIT - Trace aborted again

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

It is more complicated to generate the code like that because there
may be a lot of "break instruction" (the machine supports native
structured branch instructions) and this will require to _nest_ more
and more successive basic blocks into if statements.
In C, you will just use goto. Here I really try to simulate a forward branch.

Also, LuaJIT really behaves strangely. Because using lot of branches
to simulate forward jumps does not seem to be really the problem. The
weird thing is that for some reason, if a sequence of _lua_ statements
with no branch at all is too _big_ then no trace is compiled. If I add
for loops for each statement (I do _not_ unroll the vector
computations), then the for loops are compiled and performance is way
better.

Also, when I do:
vec2[i] = vec1[i] + vec0[i]

vec2.vec1 and vec0 also are ffi arrays (allocated with ffi.new(...))
and sse conversions instruction must be issued back and forth (for
reads and writes) since vec* are used to simulate register files with
different element size (byte,word,dword...)


Ben


On Wed, Jul 20, 2011 at 9:47 AM, Tony Finch <dot@dotat.at> wrote:
> Benjamin Segovia <segovia.benjamin@gmail.com> wrote:
>
>> I need to handle forward jumps with the idiom:
>>
>> while true do
>> {... a lot of compute ...}
>> if some_condition_on_the_lane_of_the_simd_vector then break end
>> {... a lot of compute ...}
>> break -- this one is to exit anyway
>> end
>
> Why not this?
>
>  {... a lot of compute ...}
>  if not some_condition_on_the_lane_of_the_simd_vector then
>    {... a lot of compute ...}
>  end
>
> Tony.
> --
> f.anthony.n.finch  <dot@dotat.at>  http://dotat.at/
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