[LLVMdev] Intrinsic cannot use illegal type

[Christian Sayer]

Duncan,
thanks for your hints. Truncating a legal type was actually
a nice remedy for the intrinsic - and the truncate gets eliminated
by instcombine anyway.
As of the second point, I have been disturbing myself by some
setOperationAction disorder...

Best regards,
Christian

 --
  Christian SAYER


> -----Original Message-----
> From: Duncan Sands [mailto:baldrick at free.fr]
> Sent: Tuesday, March 03, 2009 10:40 AM
> To: llvmdev at cs.uiuc.edu
> Cc: Christian Sayer
> Subject: Re: [LLVMdev] Intrinsic cannot use illegal type
>
> Hi Christian,
>
> > I use a target specific Intrinsic that returns an illegal type.
> > The idea is that this returned value shall be eliminated when the
> > Intrinsic node is lowered to a target node.
> > I realize that this is a rather late stage, since (at least)
> > SelectionDAGLowering::visitTargetIntrinsic() requires legal types,
> > and type legalization in general is also done before ISelLowering.
>
> no, type legalization is done after everything has been lowered to
> SelectionDAG nodes.  I'm not sure why visitTargetIntrinsic insists
> that types must be legal.  If there is an illegal type there then
> the type legalizer will complain later because it doesn't know how
> to legalize it, that's all.  However the type legalizer (I'm talking
> LLVM 2.5 here) allows targets to custom lower operations with illegal
> types via hooks like ReplaceNodeResults.  So if you got rid of the
> assertion in visitTargetIntrinsic and added some custom lowering
> logic, then hopefully everything will work.
>
> > The background is that the intrinsic returns a boolean value which
> > is evaluated by a branch instruction of a (special) loop.
>
> Why not have it return the boolean value in a legal type (eg: i32) and
> follow it up with a truncate to turn it into an i1 for the benefit of
> the branch?  That way you won't have to do any mucking around with the
> type legalizer at all!
>
> > The branch targets of this kind of loop are actually
> controlled and generated by  hardware. So in the end the
> intrinsic should become the branch instruction and the
> original branch should disappear.
> >
> > Is there a way to make this intrinsic go through as it is
> until instruction lowering, and to avoid type legalization on it?
>
> See above.
>
> Ciao,
>
> Duncan.
>

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