[LuaJIT] JIT bug when passing many function arguments?

[Adam Strzelecki <ono@...>]

During playing with different methods of multiplying 4x4 matrices in LuaJIT, I think I encountered strange problem with JIT. I got mmul function that takes 2x16 = 32 arguments and returns 16 arguments - multiplying two 4x4 matrices. See attached source code.

For testing I am multiplying A = A * B, where A is initially identity matrix) and B is PI/2 rotation matrix. Every 4 iterations A should be back to identity, however when JIT kicks in then a11 mysteriously changes to 0 (ZERO) and remains 0, when I turn off JIT the result is just fine I got identity every 4 iterations.

$ luajit -joff luajit-mmul.lua 
done in 0.000395 seconds
1	0	0	0
0	1	0	0
0	0	1	0
0	0	0	1

$ luajit -jon luajit-mmul.lua 
done in 0.000219 seconds
0	0	0	0
0	1	0	0
0	0	1	0
0	0	0	1

Also there's something weird in this example, if I set iter=20000000 (20 million) then it needs below <0.5 second to complete whole loop, when GCC compiled example using SSE intrinsics needs over 2 seconds to do the same and intrinsics free implementation needs over 2.2 seconds.

FYI I have also LuaJIT FFI struct based implementation using MT operators and it needs over 5 seconds to do 20 million iterations (probably due allocations discussed on other thread) but that implementation has no such JIT problem.
-- 
Adam Strzelecki

Attachment: luajit-mmul.lua
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