A 30-year pillar of compiler design just got replaced, potentially unlocking optimizations for complex languages we thought were impossible.
April 15, 2026
Original Paper
SSA without Dominance for Higher-Order Programs
arXiv · 2604.09961
The Takeaway
The paper proposes a new foundation for Static Single Assignment (SSA) form based on 'free variables' rather than 'dominance.' For decades, dominance has been the gold standard for how compilers organize and optimize code. This new approach simplifies optimizations for higher-order programs and complex language structures. It means that modern programming languages could see massive speed improvements in the next generation of compilers. For software engineers, this is a rare 're-foundation' event that could change how our code is actually executed at the lowest levels.
From the abstract
Dominance is a fundamental concept in compilers based on static single assignment (SSA) form. It underpins a wide range of analyses and transformations and defines a core property of SSA: every use must be dominated by its definition. We argue that this reliance on dominance has become increasingly problematic -- both in terms of precision and applicability to modern higher-order languages. First, control flow overapproximates data flow, which makes dominance-based analyses inherently imprecise.