[LLVMdev] Issues with clang-llvm debug info validity

[Kevin Modzelewski]

Hi all, sorry to post to both lists, but I'm running into an issue where
clang-generated debug info is deemed to be invalid by LLVM tools (throws an
assertion error in both llc and mcjit), and I'm not sure what the proper
resolution is.

Here's a test case; I last tested it on revision r210953:

$ cat test1.cpp
#include "test.h"
test::Test<int> foo1() {
    return test::Test<int>();
}

$ cat test2.cpp
namespace test {
}
#include "test.h"
test::Test<int> foo2() {
    return test::Test<int>();
}

$ cat test.h
namespace test {
template <class T>
class Test {
};
}

$ clang++ -g -emit-llvm test1.cpp -S -o test1.ll
$ clang++ -g -emit-llvm test2.cpp -S -o test2.ll
$ llvm-link test1.ll test2.ll -S -o linked.ll
$ llc linked.ll

The last step raises an assertion error, assuming you have assertions
enabled:
llc: lib/CodeGen/AsmPrinter/DwarfUnit.cpp:953: llvm::DIE*
llvm::DwarfUnit::getOrCreateTypeDIE(const llvm::MDNode*): Assertion `Ty ==
resolve(Ty.getRef()) && "type was not uniqued, possible ODR violation."'
failed

The initial introduction of the "test" namespace in test2.cpp seems to
confuse clang -- test1.cpp and test2.cpp have non-compatible debug
information for the test::Test type.  test1.cpp says that test::Test's
namespace is defined in test.h, and test2.cpp says that test::Test's
namespace is defined in test2.cpp (they both say that the class itself is
defined in test.h).  Regardless of whether LLVM tools should allow this,
this seems like the wrong output for these files?

Another related example, is if we simply defined the test::Test template in
both files (ie, manually executed the #include "test.h") and got rid of the
test2.cpp "namespace test {}" definition, we'd run into the same assertion,
without hitting the weird clang behavior with the empty namespace
pre-declaration.

It's probably also worth noting that compiling directly with clang, ie
adding a "int main() {}" function and then doing
$ clang++ -g test1.cpp test2.cpp -o test
works fine.

I'm not a C++ expert and I don't know if these template issues really are
violations of the ODR, but it feels like this should be allowed, and
somewhere in the llvm toolchain (llvm-link? DwarfUnit.cpp?) this should be
handled.  What do people think?

kmod
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