Do I need to implement CCAssignFnForCall for porting GlobalISel to AVR target?

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#1

Hi Leslie,

Long story short - no, you don't need CCAssignFnForCall.

In fact, if you look at the X86CallLowering, you'll see that it
doesn't use that either, since it can use CC_X86 directly. For ARM it
made sense to have a CCAssignFnForCall so we could reuse the code in
ARMISelLowering.

I don't know the AVR backend very well, so I can't help you figure out
what is most appropriate for the AVR target. Having a CCAssignFn
available would make it easier to use the existing infrastructure, but
in principle you should be able to get away without one if you
override ValueHandler::assignArg. After a cursory look at
AVRISelLowering, I see it has some custom code for analyzing arguments
- you'll probably have to somehow incorporate that logic into
assignArg.

Hope that helps,
Diana

#2

Hi Diana,

Thanks for your kind response!

Yes, ARM target is more complex than AVR to getEffectiveCallingConv ID https://github.com/llvm-mirror/llvm/blob/master/lib/Target/ARM/ARMISelLowering.cpp#L1559 I need to read ARM's code carefully.