Calling LowerSwitchPass causing crash in llvm 9

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1

Hi,

I am trying to call LowerSwitchPass directly in my custom pass in this way:

FunctionPass *lower = createLowerSwitchPass();
lower->runOnFunction(*f);

But it will crash when running lower->runOnFunction(*f) in llvm-9.
I was using this method in llvm-8 and it worked fine. It seems the crash happens at the first line of the LowerSwitch::runOnFunction(Function &F) in the newer llvm:

LazyValueInfo *LVI = &getAnalysis().getLVI(); //crashed here

I can’t figure out why this usage cause the compiler to crash? Am I calling function pass wrong?

Thank you for your help.

2

Sorry I found an early thread discussing this question. I guess I shouldn’t create lower switch pass like this.
However, I have another question, even if I don’t call this pass, the switch instructions will be finally compiled into binary trees, is that correct?
It seems only AMDGPU is using this pass. Is there any rule to call this pass or not?

3

There is no “switch” instruction in the target object code. It usually gets compiled into a switch table with instructions to load from it. Afaik

Zhang

4

No, I’m not talking about object code, I’m talking about llvm-ir. And there IS “switch” instruction in llvm-ir.

2019年12月27日(金) 15:50 mayuyu.io <admin@mayuyu.io>:

5

My question is that Is there any policy to decide if I should or should not call LowerSwitchPass? Anyway, I already have some assumption. Maybe if the
backend support to translate switch instructions into binary tree or switch table, then it’s not necessarily to call LowerSwitchPass in frontend. And it seems most backend
support this.