Add constexpr and consteval support for Clad project introduction blog

_posts/2024-06-05-clad-constexpr-consteval-support-intro.md

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+---
+title: "Support for constexpr and consteval in Clad"
+layout: post
+excerpt: "A GSoC 2024 project with the goal of adding support for constant expressions to Clad"
+sitemap: false
+author: Mihail Mihov
+permalink: blogs/gsoc24_mihail_mihov_introduction_blog/
+banner_image: /images/blog/gsoc-banner.png
+date: 2024-06-05
+tags: gsoc clad clang c++
+---
+
+### Introduction
+
+I am Mihail Mihov, a student during the 2024 Google Summer of Code. I will be
+working on the project "Add support for consteval and constexpr functions in
+clad".
+
+**Mentors**: Vaibhav Thakkar, Vassil Vassilev, Petro Zarytskyi
+
+
+### Briefly about Clad
+
+In mathematics and computer algebra, automatic differentiation (AD) is a set of
+techniques to numerically evaluate the derivative of a function specified by a
+computer program. Automatic differentiation is an alternative technique to
+Symbolic differentiation and Numerical differentiation (the method of finite
+differences). Clad is based on Clang which provides the necessary facilities
+for code transformation. The AD library can differentiate non-trivial
+functions.
+
+### Personal Motivation
+
+I have always liked mathematics and I also have some experience with compilers
+and find them very interesting, so when I found this project I knew that I
+would enjoy it. It combines many things that I like and I believe that doing
+something that I enjoy makes it much more likely that I will do well. C++ is
+also the first programming language that I learned so it will forever be more
+special to me.
+
+### Importance of this project
+
+Not having support for constexpr or consteval functions could be a deal-breaker
+to many projects, as these keywords have been around for some time now and the
+number of projects that use them will only increase. Also working on this
+project will require investigating what can and can't be compile-time evaluated
+and I think that we could learn something new about the already existing
+code-generation that can be improved.
+
+### Goals of the project
+
+The main goal of this project is to support differentiating functions that are
+marked as constexpr and consteval and to possibly keep the same guarantees for
+the generated derivatives.
+
+At the end of the project Clad should work on most constexpr and consteval
+functions from the C++ standard library and most other functions that a user
+could pass in.
+
+### Implementation Details and Plans
+
+Implementing this project will be mainly split into doing it for forward and for
+reverse mode, as these are the two options that Clad has for differentiating a
+function. For each of these parts I will have to look into both constexpr and
+consteval as they do have some differences that need to be solved separately.
+
+
+Implementing this project will need to start at clad's CladFunction which is
+the function type that Clad generates and is what in the end should be
+compile-time evaluated if possible. The cases where keeping the constexpr
+properties might not be possible is when loops are involved and we would need
+to implement good diagnostics in such cases, to inform the user that the code
+may not be evaluated as they would expect.
+
+### Conclusion
+
+This project should be very useful for Clad, by allowing a wider range of projects
+to use it. Along the way it's possible that there will be interesting findings which
+can be used to further improve Clad.
+
+### Related Links
+
+- [Clad repository](https://github.com/vgvassilev/clad.git)
+- [Clad documentation](https://clad.readthedocs.io)
+- [My GitHub Profile](https://github.com/mihailmihov)
+
+