[LLVMdev] Fixing VAARG on PPC64

[Hal Finkel]

On Fri, 23 Mar 2012 17:31:44 +0100
Ivan Llopard <ivanllopard at gmail.com> wrote:

> 
> Le 23/03/2012 17:02, Hal Finkel a écrit :
> > On Fri, 23 Mar 2012 09:50:12 +0100
> > Ivan Llopard<ivanllopard at gmail.com>  wrote:
> >
> >> Hi Finkel,
> >>
> >> Le 23/03/2012 05:50, Hal Finkel a écrit :
> >>> The PowerPC backend on PPC64 for non-Darwin (SVR4 ABI) systems
> >>> currently has a problem handling integer types smaller than 64
> >>> bits. This is because the ABI specifies that these types are
> >>> zero-extended to 64 bits on the stack and the default logic
> >>> provided in LegalizeDAG does not use that convention.
> >>> Specifically, for these targets we have:
> >>> setOperationAction(ISD::VAARG, MVT::Other, Expand); I thought
> >>> that I could solve this problem by:
> >>> setOperationAction(ISD::VAARG, MVT::i1, Promote);
> >>> AddPromotedToType (ISD::VAARG, MVT::i1, MVT::i64);
> >>> setOperationAction(ISD::VAARG, MVT::i8, Promote);
> >>> AddPromotedToType (ISD::VAARG, MVT::i8, MVT::i64);
> >>> setOperationAction(ISD::VAARG, MVT::i16, Promote);
> >>> AddPromotedToType (ISD::VAARG, MVT::i16, MVT::i64);
> >>> setOperationAction(ISD::VAARG, MVT::i32, Promote);
> >>> AddPromotedToType (ISD::VAARG, MVT::i32, MVT::i64); but this does
> >>> not seem to have any effect. I thought this would work because
> >>> SDValue DAGTypeLegalizer::PromoteIntRes_VAARG seems to have the
> >>> appropriate logic. Is this a bug, or am I misunderstanding how
> >>> Promote works?
> >> IMHO, you are doing it right but it looks like ISD::VAARG is not
> >> handled in SelectionDAGLegalize::PromoteNode() yet.
> >> DAGTypeLegalizer is used to legalize "non-legal" types regardless
> >> of the operation (need confirmation).
> > Thanks! That makes sense, and looking more closely at the
> > PromoteIntRes_VAARG code, it finds the type to which to promote by
> > calling TLI.getRegisterType, which won't work in this case. This
> > should not be difficult to fix.
> 
> I think that PromoteIntRes_VAARG won't even get called if VAARG has a 
> legal type, which is the case for i32 in PPC for example. If you want
> to promote VAARG nodes with a legal type to i64, you should rather
> add another case in SelectionDAGLegalize::PromoteNode(). If I
> understand correctly, it's there where promotion of legal types is
> done.
> 

Yes, I agree.

Thanks again,
Hal

> Ivan
> 
> >
> >   -Hal
> >
> >> Ivan
> >>
> >>> Thanks again,
> >>> Hal
> >>>
> >
> >



-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory