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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Hi,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>GlobalOpt may not consider demoting globals to locals in the “main” function when C is used. It used to consider “main” specifically prior to commit r253168 , for both C and C++. Since r253168, the check for the norecurse attribute may prevent “main” from being considered. This happens because the Function Attributes pass will not add the norecurse attribute to functions that have calls to library functions that aren’t themselves marked with the norecurse attribute, such as putchar. Even a call to llvm.lifetime.start, for example, will prevent a function from being considered as non-recursive as llvm.lifetime.start isn’t marked with the “norecurse” attribute.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>We have a C workload that benefits from this demotion with LTO, as some hot functions get inlined into main.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The comment in tools/clang/lib/CodeGen/CodeGenFunctions.cpp explains the reason for marking “main” with the norecurse attribute in C++:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>// If we're in C++ mode and the function name is "main", it is guaranteed<o:p></o:p></p><p class=MsoNormal>// to be norecurse by the standard (3.6.1.3 "The function main shall not be<o:p></o:p></p><p class=MsoNormal>// used within a program").<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>No such restriction exists in the C standard, as far as I can tell.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Is there anything that can be done to alleviate this restriction in C? Can we make the Function Attributes pass more aggressive, for example? Or mark certain library functions as “norecurse”, although I don’t see how this can be guaranteed.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>Sanjin<o:p></o:p></p></div></body></html>