{"title":"OOElala: order-of-evaluation based alias analysis for compiler optimization","authors":"Ankush Phulia, Vaibhav Bhagee, Sorav Bansal","doi":"10.1145/3385412.3385962","DOIUrl":null,"url":null,"abstract":"In C, the order of evaluation of expressions is unspecified; further for expressions that do not involve function calls, C semantics ensure that there cannot be a data race between two evaluations that can proceed in either order (or concurrently). We explore the optimization opportunity enabled by these non-deterministic expression evaluation semantics in C, and provide a sound compile-time alias analysis to realize the same. Our algorithm is implemented as a part of the Clang/LLVM infrastructure, in a tool called OOElala. Our experimental results demonstrate that the untapped optimization opportunity is significant: code patterns that enable such optimizations are common; the enabled transformations can range from vectorization to improved instruction selection and register allocation; and the resulting speedups can be as high as 2.6x on already-optimized code.","PeriodicalId":20580,"journal":{"name":"Proceedings of the 41st ACM SIGPLAN Conference on Programming Language Design and Implementation","volume":"42 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2020-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"3","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Proceedings of the 41st ACM SIGPLAN Conference on Programming Language Design and Implementation","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1145/3385412.3385962","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 3
Abstract
In C, the order of evaluation of expressions is unspecified; further for expressions that do not involve function calls, C semantics ensure that there cannot be a data race between two evaluations that can proceed in either order (or concurrently). We explore the optimization opportunity enabled by these non-deterministic expression evaluation semantics in C, and provide a sound compile-time alias analysis to realize the same. Our algorithm is implemented as a part of the Clang/LLVM infrastructure, in a tool called OOElala. Our experimental results demonstrate that the untapped optimization opportunity is significant: code patterns that enable such optimizations are common; the enabled transformations can range from vectorization to improved instruction selection and register allocation; and the resulting speedups can be as high as 2.6x on already-optimized code.