GlobalVariable I inserted gets removed by LTO

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1

Hello llvm-dev@

I have a pass that puts a global constant data array into the module. And another pass that gets runned by lld during LTO stage.

When I look at bytecode files corresponding to source TUs produced by clang -flto, I can see GVs inserted by my pass #1. However, when pass #2 gets to run, these GV’s are gone.

I figured out that passing -mllvm -compute-dead=0 to the linker fixes the problem, but I’m not sure if it is right thing to do. Ideally, I’d like to trick LTO to ignore only mine GVs during compute-dead analysis.

I even tried creating another function that “uses” created GV, but it also got deleted.

Any hints?

Thanks in advance.

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You should add your GVs to the llvm.used variable or the llvm.compiler.used variable (see https://llvm.org/docs/LangRef.html#the-llvm-used-global-variable). Otherwise it looks globally dead to the linker and LTO. Look at existingcalls to llvm::appendToUsed for examples.

Teresa

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You should add your GVs to the llvm.used variable or the llvm.compiler.used variable (see https://llvm.org/docs/LangRef.html#the-llvm-used-global-variable). Otherwise it looks globally dead to the linker and LTO. Look at existingcalls to llvm::appendToUsed for examples.

Teresa

Thank you, that worked!