Explain the concept of code inlining and its benefits in code optimisation.

Code inlining is a technique used in code optimization where the compiler replaces a function call with the actual code of the function at the call site. Instead of jumping to the function, the compiler inserts the function's code directly into the calling code. This process is known as inlining.

The main benefit of code inlining is the elimination of the overhead associated with function calls. When a function is called, the program needs to save the current state, including the program counter and local variables, and then jump to the function code. After the function execution, the program needs to restore the saved state. These operations consume time and memory.

By inlining the code, the function call overhead is eliminated. The compiler directly inserts the function code at the call site, reducing the need for saving and restoring the state. This results in faster execution as the program does not have to perform the function call and return operations.

Inlining also enables further optimizations. When a function is inlined, the compiler has more visibility into the code and can apply additional optimizations. For example, it can perform constant folding, where compile-time constants are evaluated and replaced with their computed values. It can also perform dead code elimination, removing unnecessary code that would have been executed if the function call was present.

Additionally, inlining can improve cache utilization. When a function is inlined, the code is placed closer to the calling code, reducing the chances of cache misses. This can lead to improved performance, especially in tight loops where the same function is called repeatedly.

However, it is important to note that code inlining may increase code size. If a function is inlined multiple times, it can result in code duplication, leading to larger executable size. This can have a negative impact on memory usage and cache efficiency. Therefore, inlining should be used judiciously, considering the trade-off between code size and performance.

In conclusion, code inlining is a technique used in code optimization to replace function calls with the actual code at the call site. It eliminates the overhead of function calls, enables further optimizations, and improves cache utilization. However, it should be used carefully to balance code size and performance.