Revise @simd documentation.

[ArchRobison]

Three changes:

• Document that break, continue, and goto are not allowed (PR Reject @simd loops with break / continue / @goto in inner loop body #8624).
• Mention that &&, ||, and ?: sometimes vectorize and use of ifelse instead of ?:.
• Clean up .rst source to avoid excessively long lines and have consistent indentation.

[ivarne]

@JuliaBackports?

Seems like this is correct for 0.3 users also? (apart from the compile-time error)

[ArchRobison]

Yes, it would be good to backport it. I'd be happy to submit a pull request for that if someone will explain how to do so (I should learn this stuff). The compile-time error sentence should be changed to something such as:

A ``break``, ``continue``, or ``goto`` in an @simd loop may cause wrong results.

[staticfloat]

Submitting a backport PR is pretty simple. First, you'll want to create a new branch based off of release-0.3, rather than master, since if you try to merge something that's based off of master, it will bring a bunch of commits along for the ride.

Probably the easiest way to do this, is to try and cherry-pick the commit here onto a new branch that is based off of release-0.3. E.g.:

$ git checkout release-0.3
$ git checkout -b my_new_branch
$ git cherry-pick a3a0d6c6d

This will attempt to apply the diff represented by a3a0d6c onto the current state of the release-0.3 branch, and you can then create a PR from my_new_branch against the release-0.3 branch on JuliaLang/julia. Note that you need to select release-0.3 in the dropdown box that typically says master when creating your pull request.

[ivarne]

I'd also recommend to keep a separate directory for release-0.3, as changing branches takes some time and might discover bugs in our makefiles.

For documentation backports, you can also push them directly into the repository and just link the commit here, instead of creating a branch and a PR.

-e -x is also two nice options to cherry-pick. -e lets you edit the commit message (eg. to add a #link to the pull request), and -x adds the sha of the original commit.

[ArchRobison]

Thanks for the pointers. I ended up creating a pull request and merging it, because I wanted to go through the steps of merging a PR (and I figured practicing on documentation was safer than code.)