[llvm] [WebAssembly] Add assembly support for final EH proposal (PR #107917)

[Derek Schuff via llvm-commits]

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@@ -147,6 +178,8 @@ let isTerminator = 1, hasSideEffects = 1, isBarrier = 1, hasCtrlDep = 1,
 // usage gets low enough.
 
 // Rethrowing an exception: rethrow
+// The new exnref proposal also uses this instruction as an interim pseudo
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dschuff wrote:

Is this just because we want to be able to support both the old and new proposals for now, or is there a more fundamental reason why it's better to use rethrow early in the pipeline and then convert it?

https://github.com/llvm/llvm-project/pull/107917