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--></style></head><body lang=en-CN link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span lang=EN-US>Hi, ALL<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> As we know, the order of compiler passes has a great influence on the results of program optimization.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> While I using llvm to compiler my test code, I changed the order of Loop Deletion pass and DSE pass(First time Loop Deletion is before DSE, the default order of FunctionSimplificationPipeline. Second time, I used DSE before Loop Deletion), the compilation method of these two sequences has produced a big performance gap, because without DSE, a variable inside loop could not be optimized for the default order of FunctionSimplificationPipeline, but the second order(DSE before Loop Deletion) works well. And I noticed that in LTODefaultPipeline , DSE is before Loop Deletion.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>So , Why there is difference of passes order between FunctionSimplificationPipeline and LTODefaultPipeline?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>And why should use Loop Deletion before DSE(or other great optimization passes) as default?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Anyone’s answers are precious to me. Thank you all.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Peakulorain<o:p></o:p></span></p></div></body></html>