[LLVMdev] Vector splitting vs widening

Nadav Rotem nrotem at apple.com
Wed Mar 6 13:40:50 PST 2013

Hi Hal, 

> The problem is essentially the following: there are no vector f32 types (yet), so the <v4i1> = setcc <v4f32> node needs to be split and scalarized. The operand splitting seems to start correctly, but because <v4i1> is itself a legal type, after splitting the node into <v2i1> = setcc <v2f32>, the process becomes confused. The operands are again split (as they should be), but it tries to widen the <v2i1> result back to <v4i1> (thus hitting the operand assertion).
> In some sense, the problem is that DAGTypeLegalizer::run decides what to do solely based on the result of calling getTypeAction(ResultVT), but it seems that in this case the operand types need to be accounted for in this determination. Enhancing the logic there to consider the result types in this case seems like it should be straightforward, but how general a problem is this? [Can this problem only happen with vsetcc nodes?]

If I understand your description correctly, the type" <v4i1> setcc ..." is split into "<v2i1> setcc ..." because of the v4f32 operands, but later on we decide to widen <v2i1> back to <v4i1> because we legalize the result ?  Can you declare <v2i1> as a legal type ? 
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