Compilers: Principles and Practice by Pearson

324 Compilers – Principles and Practice

If the common sub-expression invokes a function call, then the speed gain is even higher; consider

c = sqrt(1 – sin(x) * sin(x));

which can be rewritten as

t = sin(x);

c = sqrt(1 – t * t);

10.4.2 Loop Unwinding

Replace a loop over a small number of iterations by equivalent linear code. For example,

for(i = 0; i < 5; i++) a[i] = i;

is replaced by

a[0] = 0;

a[1] = 1;

a[2] = 2;

etc.

Here the compiler can pre-compute the addresses a[0], a[1], etc. and avoid generation of run-time

array addressing code. Also, the loop set-up and loop-control are eliminated as well.

10.4.3 Replace Index by Pointers

In this method, we replace ...