MPC: unexpected output when accessing arrays

[sebw42]

Hello, I have noticed an issue with the MPC compiler on the mpc_aws branch.
In some cases, accessing arrays containing both run-time and compile-time values returns wrong results.
Here is an example (x is set to 10 in the input file):

int main(__attribute__((private(0))) int x){
    int arr[2] = {1, x};
    return arr[0]; // returns 0
}

Compilation command:

export CARGO_MANIFEST_DIR="$PWD"; ./target/release/examples/circ --parties 2 examples/C/mpc/program.c mpc --cost-model "empirical" --selection-scheme css

Execution command:

/path/to/ABY/build/bin/aby_interpreter -m mpc -f ./scripts/aby_tests/tests/program_c -t ./scripts/aby_tests/test_inputs/program.txt -r 0 & /path/to/ABY/build/bin/aby_interpreter -m mpc -f ./scripts/aby_tests/tests/program_c -t ./scripts/aby_tests/test_inputs/program.txt -r 1

This error only seems to occur when using --selection-scheme css.

Thank you for looking into this!