[llvm] [AArch64] Use SVE to materialise some 128-bit vector constants (PR #159101)

[Paul Walker via llvm-commits]

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@@ -15236,6 +15257,11 @@ static SDValue ConstantBuildVector(SDValue Op, SelectionDAG &DAG,
     if (SDValue R = TryMOVIWithBits(UndefBits))
       return R;
 
+    // NEON doesn't have a nice way of materialising 64-bit values, but if SVE
+    // is available we have more options.
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paulwalker-arm wrote:

Up to you but I recommend keeping the common on point, thus...
```suggestion
    // Try to materialise the constant using SVE when available.
```

https://github.com/llvm/llvm-project/pull/159101