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

x = y + z
a = x + 10
p = y + z
b = p + 20
Both x and p computes same sub-expression hence generate code for x only once and p uses value of
x instead of re-computing from x & y.
After intermediate code generation it may so happen that there can be a jump statement whose target
statement is next statement itself. In this case jump statement should be avoided, which reduces code
generating time.
Constant Folding : If the assignment statement consists of only constants to the right hand side of
assignment statement. Then the value of the expression can be pre-computed.
Example: y = 2 * 5 + 6
The value of y can be computed as 16 and stored. Then the three address code generated would by
y=16 instead of
t1 = 2 * 5
t2 = t1 + 6
y = t2
This helps in constant propagation i.e, from the above example if y is used in any other expression,
instead of substituting y = 2 * 5+6 it can be substituted with y = 16.
Example:
y = 2 * 5 + 16
x = y + z
without optimization
x = 2 * 5 + 6 + z
with optimization
y = 16
x = 16 + z
Some of the operations like procedure call are very expensive, especially recursive procedure calls. In
order to reduce this, recursive procedures may be converted to iterative by providing lables. Issues
regarding procedure call it that before transferring the control to procedure. The status of procedure
has to be stored in registers. It has to be restored after procedure returns. Hence increases load and
store instructions.
Predicting program behavior
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