[LLVMdev] [llvm-commits] [llvm] r65296 - in /llvm/trunk: include/llvm/CodeGen/ lib/CodeGen/SelectionDAG/ lib/Target/CellSPU/ lib/Target/PowerPC/ lib/Target/X86/ test/CodeGen/X86/

[Scott Michel]

On Mon, Feb 23, 2009 at 2:19 PM, Nate Begeman <natebegeman at me.com> wrote:

>
> On Feb 23, 2009, at 1:46 PM, Chris Lattner wrote:
>
>  In my opinion, the proper direction for shuffles is:
>>
>> 1. Back out your patch.
>> 2. Move the functionality of "is splat" etc to method somewhere, e.g.
>> on SDNode.
>> 3. Introduce a new ShuffleVectorSDNode that only has two SDValue
>> operands (the two input vectors), but that also contains an array of
>> ints in the node (not as operands).
>> 4. Move the helper functions from #2 back into ShuffleVectorSDNode.
>>
>
> I'm working on #2 and #3 right now, and hope to land something in the next
> couple days.


Details, since this has implications for vector machine backends?

I'm just not groking how moving isSplat to SDNode eliminates BUILD_VECTOR or
deals with constant vector formation. I like the idea of a
ShuffleVectorSDNode (moves things in the direction of a bijective ISD to
SDNode mapping), but eliminating BuildVectorSDNode in its entirety doesn't
deal with constant and variable vectors.


-scooter
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