Project Stage-2 Implementation [part-1]
Tags: functionmultiversioning, aarch64, gcc
Published: 2024-06-13 18:38:46

Welcome to the SPO600 2024 Summer Project Stage-2! This summer, we're diving into the fascinating world of compiler optimization to build a prototype of Automatic Function Multi-Versioning (AFMV) for the GNU Compiler Collection (GCC) on AArch64 systems. In this blog, we’ll explore the context, for the Stage-2 of our project where we apply FMV to functions automatically, a key component of our project.

## My Task 

In this project we were assigned different roles since it is a very big process for every individual alone and we have less time. Imagine trying to understand the huge code base of GCC and then having almost 35 copies of the same project.😵‍💫 
So now lets get to the point which is my task. I was assigned the task of applying FMV cloning to the functions automatically. Description: When the appropriate command-line options are provided, the compiler should automatically clone all functions, as if the target_clone attribute was specified.
Now I know what questions are coming up in your mind , What FMV 
cloning actually is? and so on. 
I you wanna know then join me for this mini trip of applying FMV cloning.
P.S. it might not be a "MINI" trip though.

## What is Function Multi Versioning?
Function Multi-Versioning (FMV) is an optimization technique used in modern computing to enhance the performance of programs by allowing different versions of a function to be generated and used based on the specific characteristics of the hardware or runtime environment. This approach can lead to more efficient execution by leveraging specialized hardware features or optimizations tailored to specific conditions.

## Key Concepts

1. **Multiple Versions**: FMV involves creating multiple versions of a function, each optimized for different hardware capabilities or runtime scenarios. For example, a function might have one version optimized for CPUs that support a specific set of vector instructions and another version for older CPUs without these features.

2. **Selection Mechanism**: At runtime, the system determines which version of the function to execute based on the current environment. This decision is typically made using a selector function that checks the hardware capabilities or other relevant factors.

3. **Hardware Specialization**: FMV is especially useful for exploiting hardware-specific features like vector extensions (e.g., AVX, SSE on x86 architectures) or specialized instruction sets available on newer processors.

4. **Performance Optimization**: By using the most appropriate version of a function for the given context, FMV can significantly improve performance, particularly in compute-intensive applications such as scientific computing, graphics processing, and machine learning.

5. **Dynamic vs. Static Dispatch:**

    -**Static Dispatch**: The selection of the function version 
    happens at compile time. The compiler generates different 
    code paths depending on compile-time checks or target 
    specifications.

    -**Dynamic Dispatch**: The function version is selected at 
    runtime 
    based on actual hardware detection or other runtime 
    conditions.

6. **Compiler Support**: Modern compilers, such as GCC and Clang, often provide built-in support for FMV. They allow developers to specify different versions of a function and handle the dispatch logic automatically.

## Benefits of Function Multi-Versioning

- **Improved Performance**
: By using hardware-specific optimizations, FMV can enhance the execution speed of programs.
- **Flexibility**: Programs can adapt to a wide range of hardware configurations without requiring multiple separate binaries.
- **Backward Compatibility**: FMV allows newer code to run on older hardware by providing a version of functions that does not rely on newer, unsupported features.


Now the next critical question arises that how do we do this FMV cloning thing? So, as you know lets discuss this in the next blog 😉
![Giggling child](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/l5jxwyz1zlzbay1gvixb.gif)

Until then folks... Happy Coding!!!