3.4 Analyses implemented

We implemented some common analyses ¹, here shortly described. The interested reader can find further details in [1].

• Live variables (backward analysis, union): it computes, for every point in the program, which variables are alive, i.e. whose value in the point is used by the following code; assignments to variables that are not alive can be safely removed by the program.

• Constant propagation (forward analysis, intersection): it computes, for every point in the program, which variables have a constant value that can be determined statically; it allows to simplify expressions with their values.
• Very busy expressions (backward analysis, intersection): it computes, for every point in the program, which expressions appear in all the computations starting from there; in those cases, it is possible, after further tests, to hoist the expressions.
• Available expressions (forward analysis, intersection): it computes, for every point in the program, which expressions are available, i.e. whose values have already been computed; their value can be available in some register, and can be copied from there.

Suitable pretty printing functions allow the user to see the results. They can be used even to build optimized code.