[llvm-dev] Replacing ptrtoint+inttoptr with addrspacecast

[Cashman, David via llvm-dev]

Given a ptrtoint followed by inttoptr:

%tmp = ptrtoint i16 addrspace(4)* %a to i32
%b = inttoptr i32 %tmp to i8*

InstCombine will normally collapse them to a bitcast (or no-op, if the src and dst pointer types are the same).  But if the pointers are in different address spaces, as shown above, it won't, due to the following code in Instructions.cpp:

      // Cannot simplify if address spaces are different!
      if (SrcTy->getPointerAddressSpace() != DstTy->getPointerAddressSpace())
        return 0;

Is this correct?  Given that the instructions above are effectively casting the pointer between two address spaces, can/should InstCombine replace the code above with an addrspacecast?  Is there something in the LLVM language spec that makes it illegal or undesirable?

Thanks,

David
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