Static Single Assignment - The Backbone of Modern Compilers | In-Person Only

Note : This is an in-person event. Only RSVP if you are reasonably sure about attending the event. If you have a change of plans, kindly update your RSVP to 'No' to accommodate others.

Abstract :
Static Single Assignment (SSA) is a key concept in nearly every modern compiler, yet it is often introduced simply as: each variable is assigned exactly once. While this explains what SSA looks like, it does not clearly show why SSA became so important for compiler design.

In this talk, we take a step back and look at SSA from a compiler designer’s perspective. We review the real problems faced by compilers before the advent of SSA hidden value flows, complex dataflow analyses, and fragile optimization pipelines and how earlier compiler designs attempted to address these issues.

We then compare source-level code, written as linear text, with compiler intermediate representations that model programs as control-flow and data-flow graphs. Using practical examples and LLVM IR, the talk shows how SSA makes value flow explicit, simplifies analysis, and enables scalable optimization without increasing memory use or binary size.

Finally, we explore how LLVM builds and preserves SSA through program transformations, and why SSA remains the backbone of modern compiler infrastructure.