The correct solution is build settings but this should be easy to change order of arguments.

Comment by Paul Nettle (JIRA)

Side note: A terrible workaround -

I've been through the relevant parts of the SPM code and haven't found a way to inject the necessary options after the default optimization settings. The final compilation options used are placed into a YAML file in the .build directory, but I don't see a way to inject a process to modify that file before compilation is initiated (possibly one of the debug driver options can be used?)

So, for the time being I'm working around this by running swift build -c release as normal. Once the build finishes, I run a script which effectively modifies the YAML file and then re-builds. It looks something like this:

sed -i "" 's/"-O",/"-Ounchecked",/g' .build/release.yaml
rm -rf .build/release/Foo.build
rm -f .build/release/Foo
/path/to/swift-build-tool -f .build/release.yaml main -v

This is far from ideal as it requires a complete rebuild of the project (in my case, multiple modules for multiple platforms using multiple toolchains.) Yet, I will continue to do this as performance in this project is critical and this optimization provides an effective 20% perf boost.

Disclaimer: I've thoroughly tested this code to ensure that the runtime safety checks are not needed. Where necessary, I include my own logic to avoid problematic conditions.

Ah, we don't need to modify the YAML after the fact, we need to update the BuildPlan and change the order of the arguments that are generated.

Comment by Paul Nettle (JIRA)

@aciidb0mb3r - Agreed. However, I'm trying to avoid having to hack & rebuild the package manager. In my case, I'm using multiple toolchains and I don't know that I can successfully rebuild them all.

If you have any clever suggestions for temporary workarounds until I'm able to get updated toolchains, I'd love to hear them.

Hm, unfortunately no. You could build swiftpm with those toolchains and then use that but that can be very annoying.

FWIW I agree with Paul that -X* options should always come last.

#1365

Comment by Paul Nettle (JIRA)

The change covers Xswiftc, -Xcc -XLinker options, but I'm not sure it covers -Xcxx flags.

Added a PR to cover this: #1380

#1380