Troubleshooting

Build a debug version of LLV8 (debug version of LLVM might also be helpful). Isolate a faulty function, and compile only this function using LLVM, making the compilation predictable:

$LLV8_ROOT/out/x64.debug/d8 --llvm-filter=foo --predictable source.js

See if the problem is reproducible with these options:

--noinline-new 
--nouse-osr 
--nouse-inlining

Also, trace options are very helpful

--trace-opt
--trace-deopt
--trace-gc
--trace-osr
...