Available expressions make use of an expression used in one block which was computed in another block. Thus, at code generation time, code to recompute the expression need not be emitted. Example 5 shows an expression BB*12 which is computed on all paths leading to X3.
In Example 5, the expression BB*12 is available for X3 and need not be computed again for X3 if its value is saved.
Computing Available Expressions
