This is a good catch, thanks!

I'm not fond of the proposed fixes.

1. I think that changing the manual would need substantially more work. The style is inconsistent with the rest of the manual (you use concepts like "to hole" that are not used anywhere else), and I don't think that adding these as extra gc rules fits the purpose and scope of the rest of this manual section, which generally assumes that all temporaries are properly registered as roots. A minimal fix would be would to add an explicit comment to Rule 2 that temporaries are equivalent to local variables but cannot be declared with CAMLlocal, so temporaries of value type must be written to registered locals right away to "live in harmony with the GC".

2. The code fix feels too clever and annoyingly asymmetric to me. I would be in favor of sticking to the boring style where we register everything, unless there are good performance reasons to do anything more complex. In this case I don't think there are reasons to do complex (obviously the performance of this code could be improved by returning a record of (unboxed) floats instead of a tuple, but no users expressed such a need so far), so I think you should do really simple and have three locals.

The documentation extension is fine and the new code is correct yet simple. Approved. Thanks!