[LLVMdev] legalization of truncating stores in LegalizeDAG.cpp

[Akira Hatanaka]

Hi Duncan,

It seems that none of the current targets custom-lower truncating stores.

When I added code to do custom-lowering in the Mips backend, the original
node gets removed if LowerOperation returns SDValue(). This resulted in an
assertion raised when DAGCombiner::visitTokenFactor was executed.

I will add code in LegalizeDAG.cpp to check the returned value later.

On Fri, Jun 1, 2012 at 12:59 AM, Duncan Sands <baldrick at free.fr> wrote:

> Hi Akira,
>
> On 01/06/12 02:27, Hatanaka, Akira wrote:
> > In LegalizeDAG.cpp, truncating stores are custom-lowered in line
> 1314-1317:
> >
> > 1314         case TargetLowering::Custom:
> > 1315           ReplaceNode(SDValue(Node, 0),
> > 1316                       TLI.LowerOperation(SDValue(Node, 0), DAG));
> > 1317           break;
> >
> > Is there a reason it doesn't check whether the SDValue returned from
> > TargetLowering::LowerOperation is null before it replaces the original
> node with
> > the returned node? The return value is checked everywhere else
> > TLI.LowerOperation is called (line 937, for example).
> >
> >
> > 937         Tmp1 = TLI.LowerOperation(Tmp3, DAG);
> > 938         if (Tmp1.getNode()) {
> > 939           Tmp3 = Tmp1;
> > 940           Tmp4 = Tmp1.getValue(1);
> > 941         }
> > 942         break;
>
> probably it's just an oversight, because no backend needed it.
>  LegalizeDAG is
> unfortunately full of code like this.
>
> Ciao, Duncan.
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