Storage Allocation Strategies in Compiler Design

A compiler is a program that converts HLL(High-Level Language) to LLL(Low-Level Language) like machine language. In a compiler, there is a need for storage allocation strategies in Compiler design because it is very important to use the right strategy for storage allocation as it can directly affect the performance of the software.

Storage Allocation Strategies

There are mainly three types of Storage Allocation Strategies:

1. Static Allocation
2. Heap Allocation
3. Stack Allocation

1. Static Allocation

Static allocation lays out or assigns the storage for all the data objects at the compile time. In static allocation names are bound to storage. The address of these identifiers will be the same throughout. The memory will be allocated in a static location once it is created at compile time. C and C++ use static allocation.

For example:

int number = 1;
static int digit = 1;

Advantages of Static Allocation

1. It is easy to understand.

2. The memory is allocated once only at compile time and remains the same throughout the program completion.

3. Memory allocation is done before the program starts taking memory only on compile time.

Disadvantages of Static Allocation

1. Not highly scalable.

2. Static storage allocation is not very efficient.

3. The size of the data must be known at the compile time.

2. Heap Allocation

Heap allocation is used where the Stack allocation lacks if we want to retain the values of the local variable after the activation record ends, which we cannot do in stack allocation, here LIFO scheme does not work for the allocation and de-allocation of the activation record. Heap is the most flexible storage allocation strategy we can dynamically allocate and de-allocate local variables whenever the user wants according to the user needs at run-time. The variables in heap allocation can be changed according to the user’s requirement. C, C++, Python, and Java all of these support Heap Allocation.

For example:

int* ans = new int[5];

Advantages of Heap Allocation

1. Heap allocation is useful when we have data whose size is not fixed and can change during the run time.

2. We can retain the values of variables even if the activation records end.

3. Heap allocation is the most flexible allocation scheme.

Disadvantages of Heap Allocation

1. Heap allocation is slower as compared to stack allocation.

2. There is a chance of memory leaks.

3. Stack Allocation

Stack is commonly known as Dynamic allocation. Dynamic allocation means the allocation of memory at run-time. Stack is a data structure that follows the LIFO principle so whenever there is multiple activation record created it will be pushed or popped in the stack as activations begin and ends. Local variables are bound to new storage each time whenever the activation record begins because the storage is allocated at runtime every time a procedure or function call is made. When the activation record gets popped out, the local variable values get erased because the storage allocated for the activation record is removed. C and C++ both have support for Stack allocation.

For example:

void sum(int a, int b){int ans = a+b;cout<<ans;}
// when we call the sum function in the example above, 
memory will be allotted for the variable ans

Conclusion

In conclusion, different storage allocation strategies play an important role in determining the best-fit storage allocation strategy according to the need of the user as the helps in determining how the memory is going to be allocated and deallocated. Different storage allocation strategies have their own advantages and disadvantages and the choice depends on the factors like speed, memory allocation, efficiency, etc. So we can choose the allocation strategy according to the requirement.

Frequently Asked Questions

Q.1: What is the purpose of using storage allocation strategies in compiler design?

Answer:

In a compiler, there is a need for storage allocation strategies in Compiler design because it is very important to use the right strategy for storage allocation as it can directly affect the performance of the software

Q.2: Which storage allocation strategy is good if we compare Static and Dynamic Allocation?

Answer: 

It depends on many factors in some cases Static allocation will be good or in some cases Dynamic allocation. For example, in static allocation, It is easy to understand, the memory is allocated once only at compile time and remains the same throughout the program completion so the execution time will be controlled. Whereas in Dynamic allocation the memory allocation and deallocation are dynamic changes according to the user requirement. So one can choose accordingly.

Q.3: What is Stack-based storage allocation?

Answer:

Stack allocation is commonly known as Dynamic allocation. Dynamic allocation means the allocation of memory at run-time. Stack is a data structure that follows the LIFO principle so whenever there is multiple activation record created it will be pushed or popped in the stack as activations begin and ends.

Q.4: What is Heap based storage allocation?

Answer: 

Heap allocation is used where the Stack allocation lacks if we want to retain the values of the local variable after the activation record ends, which we cannot do in stack allocation, here LIFO scheme does not work for the allocation and de-allocation of the activation record. Heap is the most flexible storage allocation strategy we can dynamically allocate and de-allocate local variables whenever the user wants according to the user needs at run-time.