+ this_mask = (this_mask & -this_mask);
Unnecessary parens.
+ if (!this_mask && noisy) + warning_at (loop->loc, 0, + "insufficient partitioning available to parallelize loop");
Should this really be an unconditional warning? Isn't sequential execution a valid result of "auto"? (The spec implies that this is a possible outcome for loops inside kernels that can't be determined to be independent.)
Speaking of kernels, the testcase doesn't cover it, but maybe that's because that needs something else before it works?
Otherwise LGTM. Bernd
