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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>I’d like to evaluate a couple of extensions to a C-like language, and I was hoping to use Clang and LLVM to do that.<o:p></o:p></p><p class=MsoNormal>I ran into a couple of issues, and I’d appreciate if you could advise on the best practices to address them.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>-1- I modified Clang parser to accept the extension syntax (say a property for a function, statement, parameter, or variable), <o:p></o:p></p><p class=MsoNormal>but how do I propagate the state from Clang to LLVM IR?<o:p></o:p></p><p class=MsoNormal>I need the state to be “persistent”; i.e., IR assembly or bitcode should contain it, and IR reader should get it into memory when deserializing.<o:p></o:p></p><p class=MsoNormal>How do I do this without changing LLVM IR, IR readers and writers? Is there any way to attach “custom” state to IR classes?<o:p></o:p></p><p class=MsoNormal>I noticed that there are annotations and metadata mechanisms. Should I use one of these, which one, or there are better ways?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>-2- I need to keep this custom state (per functions, instruction, operand, variable) in LLVM IR for my optimization passes.<o:p></o:p></p><p class=MsoNormal>In addition, I’d like to leverage a few existing optimizations: the extra state will not interfere with these, but I do not want to “educate” the existing optimizations to ignore it (I still need it preserved though).<o:p></o:p></p><p class=MsoNormal>What is the best way to do this? Should I subclass existing IR classes, use metadata, use annotations, or do it somehow else?<o:p></o:p></p><p class=MsoNormal>I’ll need to query and modify extra state frequently, so the mechanism should be performant.<o:p></o:p></p><p class=MsoNormal>Some of the state should also make it to the persistent IR forms.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks in advance,<o:p></o:p></p><p class=MsoNormal>Alex<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>