[llvm-dev] GlobalVariable I inserted gets removed by LTO

[Teresa Johnson via llvm-dev]

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

On Mon, Jul 22, 2019 at 7:34 AM Gleb Popov via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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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-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |
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