[llvm] [AArch64][Codegen] Improve small shufflevector/concat lowering for SME (PR #116662)

[Benjamin Maxwell via llvm-commits]

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@@ -29274,6 +29274,11 @@ SDValue AArch64TargetLowering::LowerFixedLengthVECTOR_SHUFFLEToSVE(
     }
   }
 
+  // Try to widen the shuffle before generating a possibly expensive SVE TBL.
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MacDue wrote:

I don't think it changes the result (as all the matching above is looking for single-instruction replacements). Also, I placed it here to be consistent with the non-SVE lowering, which attempts this just before generating the Neon TBL too.  

https://github.com/llvm/llvm-project/pull/116662