Hi, everyone.
I have a problem. For example, there is an LLVM IR
%result = shl i32 %ori, 33
Accroding to cppreference, such operation should be a UB. In this case, LLVM converts the value to a poison.
So the problem is in one of the subsequent optimization PASSes that tries to cast the value to insrtuction and causes an error. Like this code:
WideInc = cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
I don’t think it’s a problem to do this directly when there is no UB.
But I want to know, should we just let this problem run its course? Or should it produce a more friendly compiler error message?
However, I think this is a UB found during optimization. We don’t even know if the pre-optimization was wrong or the input source actually has UB.