Computers as Components, 2nd Edition

5.2 Models of Programs 217

x2

abcde

2

y

1

1

w

1

x1

1

z

FIGURE 5.4

An extended data flow graph for our sample basic block.

than one edge. However,the edges are directed and all the edges for a variable must

come from a single source. We use this form for its simplicity and compactness.

The data flow graph for the code makes the order in which the operations are

performed in the C code much less obvious. This is one of the advantages of the

data flow graph. We can use it to determine feasible reorderings of the operations,

which may help us to reduce pipeline or cache conflicts. We can also use it when

the exact order of operations simply doesn’t matter. The data flow ...