llvm dev - Mar 2012 - [LLVMdev] Fixing VAARG on PPC64

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?

Thanks again,
Hal

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

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).

Ivan
>
> Thanks again,
> Hal
>

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.

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


-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory
1-630-252-0023
hfinkel at anl.gov