[llvm] [NFC][TableGen] Create valid Dag in VarLenCodeEmitter (PR #140283)

[Min-Yih Hsu via llvm-commits]

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@@ -36,6 +36,8 @@ class MyVarInst<MyMemOperand memory_op> : Instruction {
     (operand "$dst", 4),
     // Testing operand referencing with a certain bit range.
     (slice "$dst", 3, 1),
+    // Testing slice ho/lo swap.
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mshockwave wrote:

"hi/lo swap"

https://github.com/llvm/llvm-project/pull/140283