Random crashes with ABC enabled
- From: Denis Golovan <denis.golovan@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Wed, 26 Mar 2014 23:14:47 +0200
Hi
I'd like to share something I cannot call a relevant bug report. Unfortunately.
I could not create a small example to reproduce. But it happens rather often.
Still I decided to give some info on the issue. Maybe it can be useful.
Due to nature of my usage, I tend to use large native arrays I loop
over with a small amount of calculations per element. "Number
crunching", as it is usually called.
After some time I saw a real necessity in increasing "loopunroll"
parameter. It allowed me to bring my initial speed back (difference
about 100x). It was related to deeply nested functions inside my loops
where only a really small subset of paths is used. The compiler agreed
to unroll and optimize my loops again.
Unfortunately I began to notice some strange things after increasing
"loopunroll" parameter.
Sometimes immediately, sometimes after several minutes of
calculations, my program starts crashing in places where I access
native arrays in a loop. Those are pretty innocent looking loops like
:
for i=0,#arr do
if arr[i] then -- native boolean array access
...
end
end
It looks like "arr" (which is just a wrapper for a pointer to a native
array first element) points nowhere or "i" index goes into a large
negative value.
Currently I use a following code for setting parameters (some of them
are surely an overkill), but it helps to reduce the bug frequency
while still having a decent calculation speed.
jit.opt.start("maxmcode=10240", "maxtrace=3000", "maxside=400",
"maxsnap=3000", "maxirconst=2000",
"hotloop=5", "hotexit=20", "instunroll=25",
"loopunroll=100", "callunroll=25")
jit.opt.start(3)
jit.opt.start("-abc") -- without this one if happens really often
jit.flush()
I've upgraded to 2.0.3, but still no luck.
Could you suggest something?
P.S. I am under Linux x86 arch.
BR,
Denis
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