[LLVMdev] Gold plugin: emit LLVM after LTO?

Jonas Wagner jonas.wagner at epfl.ch
Tue Jun 4 03:37:36 PDT 2013


>
> > I often use the gold plugin's also-emit-llvm option to verify the final
> LLVM

 bitcode of a program. However, I realized that the gold plugin generates
>> the
>> bitcode file before running LTO optimizations, such that the changes
>> performed
>> by LTO are not reflected in the bitcode file.
>>
>> What is the reason for this behavior?
>>
>
> my guess: if the LTO optimizers crash, this is very helpful for debugging
> because it gives you the input to the optimizers.
>

This is true. It also means that if the LTO optimizers don't crash, the
bitcode is out of sync with the program. And not crashing is more common
than crashing ;)

The question is whether also-emit-llvm is an option intended for LTO
debuggers or for LLVM end-users. I'd argue that it is very useful for
end-users, and that LTO developers could get the bitcode through other
means if they are researching a crash. At least from my personal point of
view, I use also-emit-llvm frequently despite not working on LTO. How do
other people use this?

Best,
Jonas
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