What is statement simplification?
Example of statement simplification
Uses of statement simplification
Statement simplification is a code reduction technique
that replaces a series of statements in a source program with other
equivalent and simpler statements.
An example of expression simplification is given below. Consider the
following segment of an original source program:
We notice that the condition of the if statement is constant.
We therefore deduce that the then clause is the one that will
be executed and the else clause will be ignored. The original
program is equivalent to the following:
x = 1;
x = 2;
Thus we can substitute the former for the latter and get a much simpler
x = 1;
Let us again notice that statement simplification is usually a
result of constant propagation and
expression simplification. In order
to complete the circle of cooperation between these three code
reduction techniques, we will also notice that in lines following
the program segment of the previous example it is possible to
propagate the constant value 1 for the variable
x, whereas this was not possible before because it
was not known whether the then or the else
clause would be executed.
In the previous example, the statement
x = 2; of the
else clause is not reachable. A series of unreachable
statements is called dead code and can be removed
without affecting the rest of the program. Dead code removal is
another form of statement simplification. A third form is the
removal of code with no effect, that is code
that does not get executed, such as an expression statement whose
expression contains no side effects.
Current status and future work
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Last updated: Monday May 15 1995, 12:05 EET DST.