[libc++abi] Refactoring works around __dynamic_cast

[Lancern]

Summary

This commit contains refactorings around __dynamic_cast without changing its
behaviors. Some important changes include:

• Refactor __dynamic_cast into various small helper functions;
• Move dynamic_cast_stress.pass.cpp to libcxx/benchmarks and refactor it into a benchmark. The benchmark performance numbers are updated as well.

[tschuett]

libcxxabi/src/private_typeinfo.cpp

155

If you make the if explicit, you get too much indentation?

[Lancern]

Rebase onto the main branch so that CI triggers correctly

[avogelsgesang]

Hi @Lancern,

Thanks for looking into the performance of dynamic_cast and for splitting your initial patch from https://reviews.llvm.org/D137315!
Unfortunately, it looks like your patch is still not rebased onto current main. E.g., your patch claims to delete a couple of lines which are not currently on https://github.com/llvm/llvm-project/blob/main/libcxxabi/src/private_typeinfo.cpp. I marked one of those examples below. That's also why the CI currently fails (see "patch application failed" link further up on this page). Let's get that sorted out first, and as soon as the diff is correct, I will start reviewing your changes (I see little value in reviewing a non-applicable patch)

libcxxabi/src/private_typeinfo.cpp

667

E.g., here: this line of code is not currently in https://github.com/llvm/llvm-project/blob/main/libcxxabi/src/private_typeinfo.cpp but your patch still tries to delete it.

[avogelsgesang]

Ah, now I understand how you are planning to apply your changes. I assumed you first wanted to apply this patch, and then https://reviews.llvm.org/D138005 on top of it (i.e. first the refactoring, then the perf improvement). But you want to apply them exactly the other way around.

In that case, you need to set the "parent revision" here on phabricator, such that the CI knows how to apply your patch...

[Lancern]

Seems like the failed unit tests are not related to this patch nor the parent revision.

[philnik]

In D138006#3986040, @Lancern wrote:

Seems like the failed unit tests are not related to this patch nor the parent revision.

The failures on apple look related. The ones on AIX are probably just timeouts.

[avogelsgesang]

Here is one of the error messages produced on Apple

/Users/libcxx-buildkite-agent/libcxx.buildkite-agent/builds/w4-4macminivaultcom-local/llvm-project/libcxx-ci/libcxxabi/src/private_typeinfo.cpp:189:53: error: use of undeclared identifier 'dynamic_type'
                    ", %s.\n", static_type->name(), dynamic_type->name());
                                                    ^
/Users/libcxx-buildkite-agent/libcxx.buildkite-agent/builds/w4-4macminivaultcom-local/llvm-project/libcxx-ci/libcxxabi/src/private_typeinfo.cpp:191:69: warning: missing field 'dst_ptr_not_leading_to_static_ptr' initializer [-Wmissing-field-initializers]
        info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
                                                                    ^
/Users/libcxx-buildkite-agent/libcxx.buildkite-agent/builds/w4-4macminivaultcom-local/llvm-project/libcxx-ci/libcxxabi/src/private_typeinfo.cpp:193:9: error: use of undeclared identifier 'dynamic_type'
        dynamic_type->search_above_dst(&info, dynamic_ptr, dynamic_ptr, public_path, true);
        ^
/Users/libcxx-buildkite-agent/libcxx.buildkite-agent/builds/w4-4macminivaultcom-local/llvm-project/libcxx-ci/libcxxabi/src/private_typeinfo.cpp:286:69: warning: missing field 'dst_ptr_not_leading_to_static_ptr' initializer [-Wmissing-field-initializers]
        info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
                                                                    ^
2 warnings and 2 errors generated.

It seems your code inside the _LIBCXXABI_FORGIVING_DYNAMIC_CAST ifdef is incorrect. This flag is apparently only enabled on Apple

[avogelsgesang]

Seems like the failed unit tests are not related to this patch nor the parent revision.

I restarted the test run for the parent revision, and the parent revision now indeed has a green CI run

[Lancern]

Fix build issues on Apple system

[Lancern]

Rebase onto b945bb246ad9.

[Lancern]

Rebase work onto the latest main.

[Lancern]

Sync with the parent commit.

[philnik]

Thanks! LGTM.