1 Code Generation Code generator phase ... - VTU e-Learning

In order to generate more optimized code, Code optimization phase has to find out number of
variables used, their value set, those expressions which are used many times. It should also perform
some statistical analysis like-part of the code never reached, part of code which will executed many
times, procedures likely to be called. This information helps in adjusting loop structure and procedure
code to minimize execution speed.
Other Methods of Optimizations
Some of the optimization techniques are used to improve the loop statements. These are code motion
and reduction in strength of expression.
Code Motion:
Optimization is done for those statements which are executed frequently. Hence the statements whose
values do not change with respect to loop invariants should be removed from the loop.
Example:
a = 1;
while (a! = 10)
{
}
b = x + 100;
a = a + 1 ;
printf(“%d”,a);
In the above example, variable b with in while loop, is independent of loop invariant a and the value
of x do not change inside loop, hence b = x + 100 can be executed before while loop or after while
loop.
b = x + 100;
a = 1;
while (a ! = 0 )
{ a = a + 1;
}
printf (“%d”,a);
Reduce the strength of expression: If the intermediate code consists of multiplication or division, it
can be replaced by addition or subtraction, this reduces the strength of expression.
Example:
while ( i > 10)
{ i = i + 1;
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