Macro FC4SC_NO_THROW stop simulation action work unexpected when illegal bin touched

[seabeam]

Hi,

When illegal bin touched, simulation will be stopped regardless of whether it is defiened or not. The root cause is:

In fc4sc_coverpoint.hpp, line 555:

} catch(const std::exception& e) {
  std::cerr << e.what() << "\n";
  std::cerr << "sample_expression is not binded for coverpoint " << this->cvp_data->name << "\n";
  throw e;
}

It catch an exception and type is std::exception then throw, but the cvg will not catch the excpetion in fc4sc_covergroup.hpp, line 190:

    catch(illegal_bin_sample_exception &e) {
      e.update_cvg_info(this->name());
      std::cerr << e.what() << std::endl;
      #ifndef FC4SC_NO_THROW // By default the simulation will stop
      std::cerr << "Stopping simulation\n";
  throw(e);
      #endif
    }

Due to the expected exception type is illegal_bin_sample_exception not std::exception, the simulation will be stopped.

Can you help to double check it pls?

Thanks!

[SchulzSt]

Could you please provide a minimal example to test against?

[seabeam]

Could you please provide a minimal example to test against?

Refer to the examples/fir/src/stimulus.h

#include "fc4sc.hpp"

class stimulus_coverage : public covergroup {
public:
  CG_CONS(stimulus_coverage) {};

  int value = 0;

  void sample(int value) {
    this->value = value;
    covergroup::sample();
  }

  COVERPOINT(int, values_cvp, value) {
    bin<int>("zero", 0),
    illegal_bin<int>("illegal", 1)
  };
};

int main() {
  stimulus_coverage cvg;
  
  cvg.sample(1);
  cvg.sample(0);
  
  return 0;
}

log:

Illegal sample in [/values_cvp/illegal] on value [1]!
sample_expression is not binded for coverpoint values_cvp
terminate called after throwing an instance of 'std::exception'
  what():  std::exception

[seabeam]

Hi SchulzSt,

Moreover, the FC4SC_NO_THROW macro works well in:

int SAMPLE_POINT(value, values_cvp);
coverpoint<int> values_cvp = coverpoint<int> (this, "values_cvp",
    illegal_bin<int>("illegal", 1)
);

Due to the COVERPOINT macro will set has_sample_expression = true, then it capture the exception type is std::exception, while the coverpoint constructor will disable has_sample_expression, the function void coverpoint::sample(const T &cvp_val) can catch and rethrow the type of exception illegal_bin_sample_exception

[amiq-consulting]

Thanks @seabeam for the detailed breakdown and example. I successfully reproduced the bug.

The problem is indeed caused an illegal bin sample, which throws exception of type illegal_bin_sample_exception, as expected. But instead of being caught by the covergroup, it is caught by the coverpoint (and casted to std::exception when thrown again), which makes it past the covergoup.

You are also correct about the fix.
Implemented it in #21.

EDIT: also, FC4SC_NO_THROW macro could benefit from a rename, since the macro only controls exceptions related to sampling on illegal_bin. This would obviously not be backwards compatible, so maybe not worth it?

[SchulzSt]

@seabeam: Can you please check if #21 solves your issue?

[seabeam]

@seabeam: Can you please check if #21 solves your issue?

Yes, It solved in this commit of includes/fc4sc_coverpoint.hpp. Thanks