[llvm-dev] ThinLTO Problem

[chenmindong via llvm-dev]

Hi,

I'm working on enabling thinLTO for our custom backend on LLVM-8 with lld to get code size benefits from dead symbol elimination. The code in LTO::run() of LTO.cpp confuses me that, even though thinLTO is specified, runRegularLTO() will be run first and its return value determines whether runThinLTO() will be executed. 

My question is if it's clearly known that thinLTO is used, is it still necessary to execute runRegularLTO()?If it is, what's the reason behind? For now our custom backend, where distributed thinLTO is adopted, it works fine as I removed the line executing runRegularLTO(). But if I preserve it, the code fails the `if (Conf.PostInternalizeModuleHook &&!Conf.PostInternalizeModuleHook(0, *RegularLTO.CombinedModule))`, which I also don't understand, and fall through to backend() and abort there. I believe something is missed during adding the target support but cannot figure it out. Could anyone help?

Regards,
Mindong Chen