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<p class="MsoNormal">Hello LLVM people,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">after finishing Chapter 1 and 2 of the KaleidoscopeJIT tutorial, I started to play around with the code and now, I have even more questions than before. I hope that the people reading this could help me with it, to improve my understanding
about the LLVM and the JIT.<o:p></o:p></p>
<p class="MsoNormal">I have also the source code and binaries (Windows) available but because I don't know how the mailing list treats attachments (like .zip) I decided to only attach the source files - hoping it will help >o<<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">---<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">1.) Resolving undefined references<o:p></o:p></p>
<p class="MsoNormal">I wonder what the best practice is to resolve symbols that are not defined in my llvm::Module.
<o:p></o:p></p>
<p class="MsoNormal">For that purpose I created "CM_ExternalConstant", that is using "extern const int planschiValue;" and compiled it with Clang. (See CM_ExternalConstant.cpp)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">"planschiValue" is not defined in the module, so it will be unreferenced when I jit it. What is the best way to do this? I used 3 different ways:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">1.) I went over the llvm::Module before adding it to the layers. I searched for the symbol "?planschiValue@@3HB" and called "replaceAllUsesWith" to replace the symbol with the correct address. (See PlanschbeckenJIT.cpp:31)<o:p></o:p></p>
<p class="MsoNormal">2.) I set my own GeneratorFunction and provided addresses for the symbols (See PlanschbeckenJIT.cpp:95)<o:p></o:p></p>
<p class="MsoNormal">3.) I can use this->es.getMainJITDylib().define<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Each way worked fine. But I felt that way 2.) was the most annoying way, because I had to provide many other addresses. So what way is the best? Or can I 'freely' choose?<o:p></o:p></p>
<p class="MsoNormal">Is it possible to have multiple GeneratorFunctions? I would like to use the 'default' DynamicLibrarySearchGenerator plus my own lookup function.<o:p></o:p></p>
<p class="MsoNormal">Would it also be possible to replace the uses of "?planschiValue@@3HB" directly with the actuall value of "plaschiValue"? Because it is a constant?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">2.) Loading multiple modules<o:p></o:p></p>
<p class="MsoNormal">I created "CM_Orc", which has a function "int helloOrc()" - "CM_ExternalConstant" has the same function, but a different implementation. (See CM_Orc.cpp and CM_ExternalConstant.cpp) Adding both modules to the JIT will lead to an error message:<o:p></o:p></p>
<p class="MsoNormal">"Failure value returned from cantFail wrapped call<o:p></o:p></p>
<p class="MsoNormal">UNREACHABLE executed at c:\program files\llvm\include\llvm\support\error.h:708!"<o:p></o:p></p>
<p class="MsoNormal">I always thought that in this situation, one of the functions would be renamed...<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">3.) Loading multiple modules - controlled resolving<o:p></o:p></p>
<p class="MsoNormal">Finally I created "CM_PlanschiValue" this file defines a value for "planschiValue" that was referenced in "CM_ExternalConstant". (See CM_ PlanschiValue.cpp and CM_ExternalConstant.cpp) Surprisingly, if I wrote:<o:p></o:p></p>
<p class="MsoNormal">"const int planschiValue = 543210;"<o:p></o:p></p>
<p class="MsoNormal">Clang would not generate code for it.<o:p></o:p></p>
<p class="MsoNormal">But when writing:<o:p></o:p></p>
<p class="MsoNormal">"extern const int planschiValue = 543210;" it worked. Why? Why can Clang optimize away the code, when it could be referenced by a different module? Like it was!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I loaded "CM_ExternalConstant" and "CM_PlanschiValue" together, while using my own GeneratorFunction. But there was no need any more to provide an address for "?planschiValue@@3HB". Obviously, the two modules where linked - which is correct.
But what, if I don't want that for whatever reason? Would I have to rename the referenced value in the llvm::Module before adding the second module? Or should I run instead two different JITs?<o:p></o:p></p>
<p class="MsoNormal">The idea behind this is... what should I do if I have multiple modules, that are not meant to be used together but should run in the same process.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">4.) Clang and JIT optimization<o:p></o:p></p>
<p class="MsoNormal">If I compile my modules with Clang and all optimizations turned on - do I still need the TransformLayer in my JIT?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">5.) Mangling names<o:p></o:p></p>
<p class="MsoNormal">Does Clang or the LLVM provide a function to mangle from the string "const int planschiValue;" to "?planschiValue@@3HB"? Or vice versa?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">---<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I know that this are a lot questions and that I'm not good in explaining stuff - but I really hope you guys can help me to understand everything better.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Kind greetings and many thanks<o:p></o:p></p>
<p class="MsoNormal">Björn<o:p></o:p></p>
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