Enable compiler-rt on Windows

[stevapple]

Enable compiler-rt on Windows. It is required for swift-driver and other components to find clang_rt libs.

Resolves SR-NNNN.

[compnerd]

Why is this required for swift driver? There's something else that must be going on as this shouldn't be needed.

[stevapple]

clang_rt is required for “profile generate” and sanitizers.

[stevapple]

I saw in the code that at least the latter one is supported (or is going to be supported) on Windows.

[compnerd]

The profiling library doesn't work on Windows AFAIK (that is -pg isn't supported). The way to handle profiling is to use ETW.

For the sanitizers, I don't think that you can just enable compiler-rt to build the sanitizers. Not all the sanitizers work on Windows IIRC, and I think that you need to do a separate build for building the sanitizers as compiler-rt will build just the builtins.

[stevapple]

The profiling library doesn't work on Windows AFAIK (that is -pg isn't supported).

By saying this, do you mean the flag is ignored on Windows, or will trigger an error?

The way to handle profiling is to use ETW.

Does ETW have a command-line interface? Is it going to be integrated(invoked) by Swift or not?

[stevapple]

Not all the sanitizers work on Windows IIRC, and I think that you need to do a separate build for building the sanitizers as compiler-rt will build just the builtins.

At least ASan works. I don’t know where we can find sanitizers specifically optimized for Windows, but compiler-rt already provides a trustable one. Still, users should decide which sanitizer to use by themselves, the compatibility issue is okay to only be addressed in FAQ or somewhere.

[compnerd]

The issue isn’t just that the profile runtime and some of the sanitizers doesn’t work, some of then don’t even build. Microsoft is already working to get ASAN working and part of MSVC, so it is actually best to leave that support out for the time being until that work settles.

ETW is an API, not a program. You need to adjust the code generation to work with it. There’s no command line interface to it AFAIK.

[stevapple]

Based on your description, the most suitable plan for now is:

• Disable profiling on Windows, and add ETW support to TODO;
• Disable sanitizer support on Windows, until the LLVM sanitizers are stable.

If it’s okay, I’ll comment out the current codes and reject those flags. This PR and the one in compnerd/swift-build will be closed.

[compnerd]

Sure, that sounds fine, though I think that the TODOs are probably better served as issues on JIRA. I don't think that rejecting the flags is necessary, and it unnecessarily increases the amount of work to even test things. I think it is better to just setup everything, but indicate that the features are known to not work via the readme (or emitting a note/warning that the functionality is not expected to work yet)

[stevapple]

Created SR-13557

Also, see swiftlang/swift-driver#252 for the current solution

[shahmishal]

Please update the base branch to main by Oct 5th otherwise the pull request will be closed automatically.

• How to change the base branch: (Link)
• More detail about the branch update: (Link)