[llvm] [TableGen] !subst on a dag should retain name of operator (PR #141195)

[Francesco Petrogalli via llvm-commits]

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@@ -0,0 +1,18 @@
+// RUN: llvm-tblgen %s | FileCheck %s
+
+// Operator name "frag" in one_frag:$frg was not retained during !subst.
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fpetrogalli wrote:

we have operator `one_frag` named `frg`, but there is nothing that is just `frag`. Does the comment need fixing?

https://github.com/llvm/llvm-project/pull/141195