10.1.2 Local Strength Reduction
Computers add faster than they multiply, multiply faster than they
raise to powers, etc. Replacing an operator by its definition is
termed strength reduction. For example, if B
is a compile-time constant
A * B = A + A + A ... (B times)
When one of the factors is a small integer such as 2, it is worth
replacing the operator.
EXAMPLE 2 Local common subexpression elimination
T1 := 2 * A 
T1 := A + A
Example 2 replaces a multiplication by 2 with an addition. If the
factor is not a small number like 2, then sometimes a combination
of multiplications and shifts may be done.
