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The function `CGDebugInfo::EmitFunctionDecl` is supposed to create a declaration -- never a _definition_ -- of a subprogram. This is made evident by the fact that the SPFlags never have the "Declaration" bit set by that function. However, when `EmitFunctionDecl` calls `DIBuilder::createFunction`, it still tries to fill the "Declaration" argument by passing it the result of `getFunctionDeclaration(D)`. This will query an internal cache of previously created declarations and, for most code paths, we return nullptr; all is good. However, as reported in [0], there are pathological cases in which we attempt to recreate a declaration, so the cache query succeeds, resulting in a subprogram declaration whose declaration field points to another declaration. Through a series of RAUWs, the declaration field ends up pointing to the SP itself. Self-referential MDNodes can't be `unique`, which causes the verifier to fail (declarations must be `unique`). We can argue that the caller should check the cache first, but this is not a correctness issue (declarations are `unique` anyway). The bug is that `CGDebugInfo::EmitFunctionDecl` should always pass `nullptr` to the declaration argument of `DIBuilder::createFunction`, expressing the fact that declarations don't point to other declarations. AFAICT this is not something for which any reasonable meaning exists. This seems a lot like a copy-paste mistake that has survived for ~10 years, since other places in this file have the exact same call almost token-by-token. I've tested this by compiling LLVMSupport with and without the patch, O2 and O0, and comparing the dwarfdump of the lib. The dumps are identical modulo the attributes decl_file/producer/comp_dir. [0]: https://github.com/llvm/llvm-project/issues/59241 Differential Revision: https://reviews.llvm.org/D143921