[llvm] [PowerPC] extend smaller splats into bigger splats (PR #141282)

[Lei Huang via llvm-commits]

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@@ -9785,13 +9802,36 @@ SDValue PPCTargetLowering::LowerBUILD_VECTOR(SDValue Op,
                                   dl);
 
   // If the sign extended value is in the range [-16,15], use VSPLTI[bhw].
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lei137 wrote:

nit: maybe this doc need to be updated.

https://github.com/llvm/llvm-project/pull/141282