[clang] [llvm] [DebugInfo] Place local ODR-uniqued types in decl DISubprograms (PR #142166)

[Vladislav Dzhidzhoev via llvm-commits]

dzhidzhoev wrote:

> How does this work for LTO? (we'd want all inlined instances to refer to a singular abstract definition) Yeah, looks like that's broken (the abstract origins are not shared - they're duplicated in every translation unit).

But the notion of "abstract" subprogram pops up only during DWARF generation, doesn’t it?
On the level of LLVM IR, we don’t have a way to distinguish between abstract and concrete DISubprogram, if I get it right. 



> We should fix that. We have mangled names on functions like we do for types, so we could use the same approach to deduplicate them via mangled name as a key? (for types this mangled name field was introduced specifically as a deduplication key (I think initially for type units, then for LTO merging, but maybe it was the other way around) - currently the linkage name for functions isn't a load bearing key, but it could become one, or perhaps needs to be a distinct key compared to the mangled name - in the case of internal functions/types they might have a mangled name, but not allow deduplication (for internal linkage types, we omit the mangled name/deduplication key))

It seems something similar is done for declarations of composite type member subprograms, according to https://llvm.org/docs/LangRef.html#disubprogramdeclaration :

> When spFlags: DISPFlagDefinition is not present, subprograms describe a declaration in the type tree as opposed to a definition of a function. In this case, the declaration field must be empty. If the scope is a composite type with an ODR identifier: and that does not set flags: DIFwdDecl, then the subprogram declaration is uniqued based only on its linkageName: and scope:.


https://github.com/llvm/llvm-project/pull/142166