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
This directory contains testcases that the verifier is supposed to detect as
malformed LLVM code. Testcases for situations that the verifier incorrectly
identifies as malformed should go in the test/Assembler directory.
997dc7e00f