Add arm64 support to CMake build

[neonichu]

This is pretty speculative, I just copied the SwiftSupport.cmake from swift-argument-parser which seems to have support for arm64.

[neonichu]

Testing this out first via cross-repo testing on a Swift PR.

[tomerd]

cc @lorentey @compnerd @shahmishal

if this works I think we would also need a new tag and update swift build script to pull it

[tomerd]

@neonichu @lorentey @compnerd we need this (+ new tag) to unblock swiftlang/swift-package-manager#3632. do you think this is ready?

[lorentey]

I'm ready to hit the merge button & tag a release if y'all say it works as expected.

@swift-ci test

[compnerd]

I think that this is slightly regressing the behavior. I think that there are now out of sync (foundation, dispatch, etc have a copy as well). The install layout has evolved a bit from the 5.1/5.2 days. All the platforms now support the directory layout as well. Windows prefers that layout with the module being triple named rather than just arch I believe.

[neonichu]

@compnerd Do you have a suggestion on which version of this file we should standardize? Is Foundation the canonical one?

[compnerd]

The changes that I believe haven't been synced are the ones to _install_target here:
https://github.com/compnerd/swift-win32/blob/main/cmake/Modules/SwiftSupport.cmake#L53-L92

The changes that you have to the get_swift_host_arch we can get away with as we do not expect someone to define CMAKE_OSX_DEPLOYMENT_TARGET on non-Darwin targets, but this seems somewhat fragile. I think that this might be a better check:

elseif ("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "AArch64|ARM64")
  if(CMAKE_SYSTEM_NAME MATCHES Darwin)
    set("${result_var_name}" "arm64" PARENT_SCOPE)
  else()
    set("${result_var_name}" "aarch64" PARENT_SCOPE)
  endif()

[neonichu]

OK, thanks. I updated it, but it seems like we do need the lowercase "arm64" in the check of CMAKE_SYSTEM_PROCESSOR, otherwise this doesn't work on my M1 machine.

[compnerd]

Hmm, I wonder if we should do string(TOUPPER or string(TOLOWER to make sure that we do the case insensitive match. That is rather annoying, but we shouldn't be gating this on that.

[compnerd]

I think that you missed the update for the second half of the change (the install location).

[neonichu]

@swift-ci please test

[neonichu]

OK, I removed the unnecessary changes and tested this locally, seems to work fine.

[compnerd]

LGTM; we should verify that the Linux ARM64 builds are unimpacted, but otherwise, LGTM

[neonichu]

Actually, I think I flipped it with my last edits, it'll now use "aarch64" on Darwin.

[tomerd]

@compnerd @lorentey how are we feeling about this?

[lorentey]

I'm happy to merge & tag as soon as someone confirms this is what we want. 😉

@neonichu, did you mean to swap the spellings? IIUC Swift Argument Parser uses arm64 on Darwin, and aarch64 elsewhere.

[neonichu]

@swift-ci please test

[neonichu]

@lorentey Yes, absolutely. I failed to push my latest changes. Interestingly, it seemed to have no impact on being able to build, either version worked.

[tomerd]

@lorentey I guess we need a new tag, so we can pull this into toolchain + SwiftPM. Do you have any other pending changes?