C file not instrumented for coverage, bad expr node kind

I am using the legacy_code tool to generate some S Functions, then I want the S Functions to be under analysis by the simulink coverage toolbox.

I am setting to true the flag to use coverage:

def.Options.supportCoverage = true;

But I get the following error:

"lib_control.c", line 254: error: bad expr node kind (b:\matlab\polyspace\src\shared\cxx_front_end_kernel\edg\src\cp_gen_be.c, line 14084)
Warning: File "lib_control.c" not instrumented for coverage because of previous error 
> In codeinstrum.internal.LCInstrumenter/instrumentAllFiles
  In codeinstrum.internal.SFcnInstrumenter/instrument
  In slcovmexImpl
  In slcovmex (line 48)
  In legacycode.LCT/compile
  In legacycode.LCT.legacyCodeImpl
  In legacy_code (line 101)
  In generate_sfun (line 70)   

In the C code I have the following kind of functions:

void controller( int n_var,
                 double my_input,
                 double my_output )

{
    double my_var[n_var];    
    for ( int i=0; i<n_var; i++ )
    {
        my_output = my_input + my_var[i];
    }
}

The compiler is complaining about this line:

double my_var[n_var];

Do I have to do something to declare variables like this, so they can be included in the coverage analysis?