[llvm] [SelectionDAG] Use ExpandIntRes_CLMUL to expand vector CLMUL via narrower legal types (PR #184468)

[David Green via llvm-commits]

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@@ -1329,6 +1329,8 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
       setOperationAction(ISD::CTLS, VT, Legal);
     setOperationAction(ISD::BITREVERSE, MVT::v8i8, Legal);
     setOperationAction(ISD::BITREVERSE, MVT::v16i8, Legal);
+    setOperationAction(ISD::BITREVERSE, MVT::v4i16, Custom);
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davemgreen wrote:

Does this need to be added? IIUC it is just added to use Custom as the equivalent of a cost model and the expansion will otherwise be similar. Could it check the expansion is legal instead?

https://github.com/llvm/llvm-project/pull/184468