ALT To optimize a program, a compiler needs precise information about it. Significant effort is dedicated to improving the ability of compilers to analyze programs, with the expectation that more information results in better optimization. But this assumption does not always hold: due to unexpected interactions between compiler components and phase ordering issues, sometimes more information leads to worse optimization. This can lead to wasted research and engineering effort whenever compilers cannot efficiently leverage additional information. In this work, we systematically examine the extent to which additional information can be detrimental to compilers. We consider two types of information: dead code, i.e., whether a program location is unreachable, and value ranges, i.e., the possible values a variable can take at a specific program location. Given a seed program, we refine it with additional information and check whether this degrades the output. Based on this approach, we develop…

ALT Listing 2. Optimization inconsistency example: the current upstream version of GCC -Os optimizes away all controlflowintheoriginalprogram.Refiningtheprogramwithadditionalinformation,leadstoanunexpected behavior: the compiler fails to optimize the refined program and generates significantly more complex code. Adapted from bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112545