Class GlobalUse

A use that models a synthetic “last use” of a global variable just before a function returns.

We model global variable flow by:

• Inserting a last use of any global variable that’s modified by a function
• Flowing from the last use to the VariableNode that represents the global variable.
• Flowing from the VariableNode to an “initial def” of the global variable in any function that may read the global variable.
• Flowing from the initial definition to any subsequent uses of the global variable in the function body.

For example, consider the following pair of functions:

int global;
int source();
void sink(int);

void set_global() {
  global = source();
}

void read_global() {
 sink(global);
}

we insert global uses and defs so that (from the point-of-view of dataflow) the above scenario looks like:

int global; // (1)
int source();
void sink(int);

void set_global() {
  global = source();
  __global_use(global); // (2)
}

void read_global() {
 global = __global_def; // (3)
 sink(global); // (4)
}

and flow from source() to the argument of sink is then modeled as follows:

1. Flow from source() to (2) (via SSA).
2. Flow from (2) to (1) (via a jumpStep).
3. Flow from (1) to (3) (via a jumpStep).
4. Flow from (3) to (4) (via SSA).