What every scientific programmer should know about compiler optimizations?

Abstract

Compilers are an indispensable component in the software stack. Besides generating machine code, compilers perform multiple optimizations to improve code performance. Typically, scientific programmers treat compilers as a blackbox and expect them to optimize code thoroughly. However, optimizing compilers are not performance panacea. They can miss optimization opportunities or even introduce inefficiencies that are not in the source code. There is a lack of tool infrastructures and datasets that can provide such a study to help understand compiler optimizations. In this paper, we investigate an important compiler optimization---dead and redundant operation elimination. We first develop a tool CIDetector to analyze a large number of programs. In our analysis, we select 12 representative programs from different domains to form a dataset called CIBench. We utilize five compilers to optimize CIBench with the highest optimization options available and leverage CIDetector to study each generated binary. We provide insights into two aspects. First, we show that modern compilers miss several optimization opportunities, in fact they even introduce some inefficiencies, which require programmers to refactor the source code. Second, we show how compilers have advanced in a vertical evolution (the same compiler of different release versions) and a horizontal comparison (different compilers of the most recent releases). With empirical studies, we provide insights for software engineers, compiler writers, and tool developers.