[LLVMdev] to lower "write to argument pointer"

[Tom Stellard]

On Tue, Jul 29, 2014 at 12:25:55AM -0400, kewuzhang wrote:
> Drear there:
> 
> The problem I have is  to lower an intrinsic function like this
> ”
> float @llvm.write.arg(flaot %src, float* %dst)
> “
> I am lowering it with INTRINSIC_W_CHAIN,  so the return value and the value to write to dst are generated with some operations using src:
> 
> "
>  // it is the frame index node corresponding to input pointer
> SDvalue frindex = Op.getoperand(3);
> …
> SDValue returnValue = DAG.getNode(myNode1, DL, VT….);
> 
> SDValue dstValue 	= DAG.getNode(myNode2, DL, VT….);
> 
> // to save the value to dst pointer, I think I need some call like 
> SDValue dstOut = DAG.getStore(chain, DL, dstValue, FrameIndex, MachinePointerInfo(), false, false, 0);
> 
> “
> I have two questions here: 
> (1)  should I return some merges values( returnValue, DstValue) ? or only return returnValue is right? ( the dag dumped out  looks better if I return the merged values)

Since INTRINSIC_W_CHAIN has two values, whatever you lower it to should
have two: The result and the chain.  You canuse MERGE_VALUES for that.

> (2) How the FrameIndex should be computed? I use  DAG.getFrameIndex((dyn_cast<FrameIndexSDnode>( frindex.getNode()))->getIndex(), i32), not confident it is correct, any good examples to understand to this?
> 

Is the FrameIndex one of the inputs to the intrinsic, or are you trying
to create a new FrameIndex?

-Tom

> Best
> 
> Kevin

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