Single assignment compiler, single assignment architecture: Future gated single assignment form*; Static single assignment with congruence classes

Document Type

Conference Proceeding

Publication Date



Department of Computer Science


We present a new static single assignment form which can be used by an optimizing compiler as its internal representation and the micro-architecture as its instruction set. This representation, Future Gated Single Assignment Form (FGSA), directly represents the use-def relationship of variables by employing the concept of congruence classes and the concept of future dependencies. We show that FGSA is efficiently computable by using a series of T1/T2 transformations, yielding an expected linear time algorithm for the construction of single assignment form. Our interval analysis method includes a novel transformation TR which eliminates irreducible loops without node splitting and combines computation of single-assignment form with irreducible loop elimination. The algorithm produces pruned single assignment form, rendering a separate pruning step unnecessary. In practice, the FGSA approach results in an average reduction of 7.7%, with a maximum of 67% in the number of gating functions compared to the pruned SSA form on the SPEC2000 benchmark suite, owing to its ability to represent dataflow within a congruence class by using a single gating function. We illustrate that FGSA is convenient to use as an internal representation in an optimizing compiler by presenting two case studies of optimization algorithms on FGSA.

Publisher's Statement

Copyright 2014 ACM. Publisher’s version of record: https://doi.org/10.1145/2581122.2544158

Publication Title

CGO '14 Proceedings of Annual IEEE/ACM International Symposium on Code Generation and Optimization