[llvm-dev] [GlobalISel] A Proposal for global instruction selection

[Mehdi Amini via llvm-dev]

> On Jan 8, 2016, at 1:34 AM, David Chisnall via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> On 7 Jan 2016, at 19:47, Quentin Colombet <qcolombet at apple.com> wrote:
>> 
>> Indeed, you said that inttoptr instruction is not a no-op on your architecture, whereas the language reference says:
>> “The ‘inttoptr‘ instruction converts value to type ty2 by applying either a zero extension or a truncation depending on the size of the integer value. If value is larger than the size of a pointer then a truncation is done. If value is smaller than the size of a pointer then a zero extension is done. If they are the same size, nothing is done (no-op cast).”
>> 
>> The bottom line is that IMHO, if you rely on inttoptr/ptrtoint instructions to do the conversion from fat pointers to plain integers you are abusing the IR.
>> 
> 
> I believe that this is somewhere where the IR specification needs to evolve.  Currently, we have no in-tree architectures where pointers are not integers and so that definition is appropriate.  Adding a new pair of IR instructions for integer-to-pointer and pointer-to-integer conversions and not calling them inttoptr / ptrtoint is likely to be far more confusing.

I think this would deserve its own RFC email thread.

— 
Mehdi