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I'm trying to implement a codegen (I seek for assembler listing only, not a binary code) for custom architecture which doesn't have hardware implementation of integer division. I use clang frontend and get symbols like __divsi3 in my assembler listing. I see an implementation of __divsi3 in compiler_rt library of LLVM. How could I use this?

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  • You can adapt the code from this answer. Commented Sep 29, 2012 at 8:38
  • I don't ask for algorithm of division, but for a way of using standard library function. Commented Sep 29, 2012 at 9:12
  • Then I don't understand your question. Can you elaborate it or provide an example of what you want? Commented Sep 29, 2012 at 9:14
  • I suppose you should compile libcompile_rt into bitcode and then substitute calls like __divsi3 with their code. Commented Sep 30, 2012 at 13:21

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You'll use your new compiler to compile the appropriate functions in compiler-rt that your processor is missing. Then include the compiler-rt library at link time so the unresolved symbol can be resolved.

__divsi3 is just a simple C function that uses simpler operations to perform the division that your architecture doesn't support.

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Sounds reasonable, thank you. The only gotcha I have, is that I have no control on linkage, my codegen just generates asm. And I'm not sure that the current setting allows for multi-file linkage. I have to elaborate on asm-to-bin tool documentation — whether it can link multiple asm files.
No problem. Just compile the compiler-rt files to bitcode, use llvm-link to link the rt objects with your application code bitcode, and then run the result through your code generator.
I found necessary linker option. But I have another problem now: how to told LLVM to add an external declaration for the function which implements integer division…

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