Static single assignment form for machine code

Abstract

Static Single Assignment (SSA) is an effective intermediate representation in optimizing compilers. However, traditional SSA form and optimizations are not applicable to programs represented as native machine instructions because the use of dedicated registers imposed by calling conventions, the runtime system, and target architecture must be made explicit. We present a simple scheme for converting between programs in machine code and in SSA, such that references to dedicated physical registers in machine code are preserved. Our scheme ignores all output- and anti-dependences imposed by physical registers while a program is in SSA form, but inserts compensation code during machine code reconstruction if any naming requirements have been violated. By resolving all mismatches between the two representations in separate phases, we are able to utilize existing SSA algorithms unaltered to perform machine code optimizations.