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More precise construction of static single assignment programs using reaching definitions


Publication Type:

Journal article


Journal of Systems and Software



The Static Single Assignment (SSA) form is an intermediate representation used for the analysis and optimization of programs in modern compilers. The φ-function placement is the most com- putationally expensive part of converting any program into its SSA form. The most widely-used φ-function placement algorithms are based on computing dominance frontiers (DF). However, this kind of algorithms works under the limiting assumption that all variables are defined at the be- ginning of the program, which is not the case for local variables. In this paper, we introduce an innovative φ-placement algorithm based on computing reaching definitions (RD), which generates a precise number of φ-functions. We provided theorems and proofs showing the correctness and the theoretical computational complexity of our algorithms. We implemented our approach and a well-known DF-based algorithm in the Clang/LLVM compiler framework, and performed experi- ments on a number of benchmarks. The results show that the limiting assumption of the DF-based algorithm when compared with the more accurate results of our RD-based approach leads to gen- erating up to 87% (69% on average) superfluous φ-functions on all benchmarks, and thus brings about a significant precision loss. Moreover, even though our approach computes more informa- tion to generate precise results, it is able to analyze up to 92.96% procedures (65.63% on average) of all benchmarks with execution time within twice the execution time of the reference DF-based approach.


author = {Abu Naser Masud and Federico Ciccozzi},
title = {More precise construction of static single assignment programs using reaching definitions},
isbn = {0164-1212},
month = {April},
year = {2020},
journal = {Journal of Systems and Software},
url = {}