[llvm] [AArch64] Use firstp for SVE2.2 cttz.elts (PR #221182)

[Vimal Patel via llvm-commits]

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@@ -9169,8 +9153,12 @@ SDValue AArch64TargetLowering::LowerOperation(SDValue Op,
     }
 
     SDValue Pg = getPredicateForVector(DAG, DL, VT);
-    SDValue NewCttzElts =
-        DAG.getNode(AArch64ISD::CTTZ_ELTS, DL, MVT::i64, Pg, CttzOp);
+    // We preserve the poison semantics here to avoid the poison path from being
+    // affected by the checks emitted for the no-poison case.
+    unsigned Opcode = Op.getOpcode() == ISD::CTTZ_ELTS_ZERO_POISON
+                          ? AArch64ISD::CTTZ_ELTS_ZERO_POISON
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pvimal816a wrote:

Discussed offline. The conclusion is that the scalable predicate must be created when the length of the original fixed vector is known. Once the fixed-length data vector is converted to scalable vector it would be tedious to construct a scalable predicate.

https://github.com/llvm/llvm-project/pull/221182