Add Support for Applying Mutations Only at Given Mutation IDs

[JonathanFoo0523]

The current implementation of Dredd applies all possible mutations to the entire C/C++ file. This could significantly impact the runtime performance of the program built from the mutated file, as there are substantial increases in branching and the invocation of dredd functions. This problem is magnified in large files.

We would like a Dredd mode that applies mutations only at specified IDs. For instance, when applying Dredd to the following C file with the command dredd sample.c --mutation-info-file temp.json

int main() {
    int foo = 0;
    foo = 1;
    foo += 2;
    return 0;
}

The mutated main function will be

int main() {
    int foo = __dredd_replace_expr_int_zero(0, 0);
    if (!__dredd_enabled_mutation(15)) { __dredd_replace_binary_operator_Assign_arg1_int_arg2_int(&(foo) , __dredd_replace_expr_int_one(1, 2), 5); }
    if (!__dredd_enabled_mutation(31)) { __dredd_replace_binary_operator_AddAssign_arg1_int_arg2_int(&(foo) , __dredd_replace_expr_int_constant(2, 16), 21); }
    if (!__dredd_enabled_mutation(34)) { return __dredd_replace_expr_int_zero(0, 32); }
}

We want a dredd mode which could be called with something like dredd sample.c --mutation-info-file temp.json --made-available-mutation="0, 15, 34" to produce mutated file with main as

int main() {
    int foo = __dredd_replace_expr_int_zero(0, 0);
    if (!__dredd_enabled_mutation(15)) {  foo = 1; }
    foo += 2;
    if (!__dredd_enabled_mutation(34)) { return 0; }
}

Note that mutation id 1 is made available too as a side effect.

@afd suggest this could be implemented by:

• first does a "dry run" pass where it works out all the mutations that it could apply, and possibly even produces the output .json file with the mutation tree, but does not actually apply any mutations to the source code
• second, does a "really mutate" pass where it reads from a file the ids of all mutants that should be made available, and then does its thing, but skipping any mutants with ids not on the list.

[JonathanFoo0523]

Is it necessary to go further to disallow mutation id 1?

Should I change

static int __dredd_replace_expr_int_zero(int arg, int local_mutation_id) {
  if (!__dredd_some_mutation_enabled) return arg;
  if (__dredd_enabled_mutation(local_mutation_id + 0)) return 1;
  if (__dredd_enabled_mutation(local_mutation_id + 1)) return -1;
  return arg;
}

to

static int __dredd_replace_expr_int_zero(int arg, int local_mutation_id) {
  if (!__dredd_some_mutation_enabled) return arg;
  if (__dredd_enabled_mutation(local_mutation_id + 0)) return 1;
  return arg;
}

What about other mutation points sharing the same __dredd_replace_expr_int_zero function?