The classic definition of control dependencies is that every
instruction after a branch is control dependent on the branch, and
must wait for the branch to execute before they may execute.
In the example below, instructions 2 through 7 are control
dependent on instruction 1, a branch.
1: if (a == b) { //or, in branch format: if (a != b) goto 3;
2: z = y + x; }
3: d = e * f;
4: g = d - h;
5: if (x == y) { //or, in branch format: if (x != y) goto 7;
6: u = y + e; }
7: j = k - m;
However, instructions 3 through 7 will execute regardless of how the
branch at 1 executes.
Therefore, applying this concept (minimal control dependencies),
instructions 3 through 7
are not control dependent on instruction 1, and may execute
concurrently with it. This implies that in many cases branches can
execute in parallel and out-of-order with other branches; in the
example, the branch at 5 can be executed before or at the same time
as the branch at 1.
The execution of branches in parallel is essential for the exploitation
of high levels of Instruction Level Parallelism.
