[llvm] [llvm] Add comment and assert for CloneModule edge case (PR #67734)

[Yaxun Liu via llvm-commits]

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@@ -268,6 +268,8 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
 
   // Loop over all of the instructions in the new function, fixing up operand
   // references as we go. This uses VMap to do all the hard work.
+  assert(!OldFunc->empty() && "Cannot clone module with empty function body.\
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yxsamliu wrote:

what if the function is really empty?

How about use OldFunc->assertModuleIsMaterialized() instead?

https://github.com/llvm/llvm-project/pull/67734