[llvm] [AArch64] Select same-input SVE EXT with EXT_ZZI_CONSTRUCTIVE (PR #227749)

[Sander de Smalen via llvm-commits]

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@@ -1187,6 +1187,10 @@ let Predicates = [HasSVE_or_SME] in {
 
   def EXT_ZZI_CONSTRUCTIVE : UnpredRegImmPseudo<ZPR8, imm0_255>;
 
+  let AddedComplexity = 3 in 
+  def : Pat<(nxv16i8 (AArch64ext nxv16i8:$Zs, nxv16i8:$Zs, (i32 imm0_255:$imm))),
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sdesmalen-arm wrote:

@gbossu added support for mapping `vector_splice[_left]` to `EXT_ZZI_CONSTRUCTIVE` in #152554.

We could make AArch64ext a PatFrag that also matches `llvm.vector.splice.left`.

Alternatively, if this code comes from ACLE code, Clang could probably also emit the `llvm.vector.splice.left` directly (as that now seems a duplicate of the SVE intrinsic)

https://github.com/llvm/llvm-project/pull/227749