std::type_index equality broken with LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=OFF

[llvmbot]

Bugzilla Link	45549
Resolution	FIXED
Resolved on	Jan 26, 2021 06:23
Version	9.0
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@k15tfu,@ldionne,@mclow
Fixed by commit(s)	2464d81

Extended Description

When using LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=OFF, distinct classes with the same name, each in a different TU and anonymous namespace, are considered equal by std::type_index.

LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=OFF is used in the libc++ shipped with Xcode as of Xcode 11.4. The bug does not occur in Xcode 11.3.1, the previous version. LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT was introduced in 2405bd6 for LLVM 9.0.0.

See https://gist.github.com/ryb-ableton/1805b61e2d0976de4ba04c2aa2f5992b for a minimal test case.

May be related to #34255

---

Steps to reproduce on Linux/x86:

1. Build and install libc++ 9.0 or 10.0 by passing -DLIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=OFF to cmake
2. Download and extract a zip of the Gist linked above
3. Run "bash ./build_and_run"

Steps to reproduce on macOS:

1. Install and select Xcode 11.4, which uses LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=OFF by default
2. Download and extract a zip of the Gist linked above
3. Run "bash ./build_and_run"

Actual Output:

Assertion failed: (registry[0] != registry[1]), function main, file main.cpp, line 13.
./run: line 4: 39942 Abort trap: 6 ./test
Failure

Expected Output:

Success

[llvmbot]

assigned to @ldionne

[ldionne]

Thanks for the report and the nice analysis of the issue!

I fixed the issue on Apple platforms in 2464d81, and I'm adding tests so we don't regress in https://reviews.llvm.org/D78963.

[llvmbot]

Nice, thanks for the quick fix!