[llvm-dev] ptrtoint > addrspacecast is disallowed

[Kavindu Gimhan Zoysa via llvm-dev]

> The semantics of addrspacecast (
> https://llvm.org/docs/LangRef.html#addrspacecast-to-instruction) are:
>
> The ‘addrspacecast’ instruction converts the pointer value ptrval to type
> pty2. *It can be a **no-op cast** or a complex value modification,
> depending on the target and the address space pair.* Pointer conversions
> within the same address space must be performed with the bitcast
> instruction. Note that if the address space conversion is legal then both
> result and operand refer to the same memory location.
>
> So whether it is valid for instcombine to optimise your example depends on
> the target. It would be wrong for instcombine to unconditionally optimise
> this to i64 3098316506530080114. It might be possible to extend it to
> optimise this when the optimisation is valid by getting extra information
> from the target, there is a isNoopAddrSpaceCast function already that can
> be used to determine whether it is valid, but the function you are looking
> at is target-independent, it cannot get target info. It will require some
> thought on the design.
>
Thank you, Your explanation helps me to understand this. So it is wrong to
look at the *visitPtrToInt *method?
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp#L2046
After going through that method I found that it calls
https://github.com/llvm/llvm-project/blob/main/llvm/lib/IR/Instructions.cpp#L2797,
which disallow ptrtoint -> addrspacecast.
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