[LLVMdev] Alignment of constant loads

[Paul Redmond]

Hi Dan,
> It looks like the best way to do this is to visit the handful of
> places in legalize that create loads from constant pools and
> add alignment parameters to the getLoad/getExtLoad calls.
>
> If you move the handling of Alignment==0 out of ScheduleDAGEmit.cpp
> and into SelectionDAG::getConstantPool, you can then have legalize
> read the alignment from the node, instead of making its own
> decision:
>    cast<ConstantPoolSDNode>(CPIdx)->getAlignment()
>
>   
I followed your suggestion but I've come across a bit of a snag. If you 
get the alignment in LegalizeDAG using:

SDValue CPIdx = DAG.getConstantPool(LLVMC, TLI.getPointerTy());
unsigned Alignment = cast<ConstantPoolSDNode>(CPIdx)->getAlignment();

The ConstantPoolSDNode is created using MVT i32 (TLI.getPointerTy()) and 
the alignment is 4 bytes. It seems there is not enough information to 
know that the final MVT will be v4f32 so passing the alignment to 
getLoad/getExtLoad in LegalizeDAG will still generate unaligned loads 
for constant vectors.

Any ideas?

thanks,
Paul