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Keep side-effect-less expression statements when wanted
This is an even simpler version of #140.
CIL removes side-effect-less standalone expressions completely, but this makes Goblint unsound as it misses a race. For example in
#include <pthread.h>
#include <stdio.h>
int myglobal;
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex2 = PTHREAD_MUTEX_INITIALIZER;
void *t_fun(void *arg) {
pthread_mutex_lock(&mutex1);
myglobal; // RACE!
pthread_mutex_unlock(&mutex1);
return NULL;
}
int main(void) {
pthread_t id;
pthread_create(&id, NULL, t_fun, NULL);
pthread_mutex_lock(&mutex2);
myglobal=myglobal+1; // RACE!
pthread_mutex_unlock(&mutex2);
pthread_join (id, NULL);
return 0;
}
Obviously any sensible compiler just optimizes away, but I don't think the standard demands such optimization. It just says the expression is evaluated:
The expression in an expression statement is evaluated as a void expression for its side effects.
The semantic descriptions in this International Standard describe the behavior of an abstract machine in which issues of optimization are irrelevant.
I think the problem is that the CIL AST has no construct that corresponds to this. It's only Cabs which as A.COMPUTATION
.