dagop: minor python optimization to `headrevs` Less lookup and less function call never hurt. This provides a small speedup on various run of the 'heads()' revset. This also buys back some of the slow down we observed in the previous changesets for single value lookup. Performance number: 0) before dagop.headrevs usage 1) after dagop.headrevs usage 2) after this change revset: heads(all()) plain min max first last reverse rev..rst rev..ast sort sor..rst sor..ast 0) 0.036503 0.032564 0.030024 0.032378 0.030887 0.036367 0.031713 0.032205 0.036467 0.032286 0.030300 1) 0.036668 0.035347 108% 0.035611 118% 0.035358 109% 0.035726 115% 0.036411 0.035261 111% 0.036096 112% 0.036052 0.035095 108% 0.035792 118% 2) 0.034254 93% 0.034482 0.035003 0.034353 0.033754 94% 0.034689 0.034361 0.035059 0.034636 0.034662 0.035465 revset: heads(-10000:-1) plain min max first last reverse rev..rst rev..ast sort sor..rst sor..ast 0) 0.003936 0.003218 0.003227 0.003302 0.003328 0.003848 0.003305 0.003252 0.003839 0.003306 0.003279 1) 0.003870 0.003785 117% 0.003821 118% 0.003780 114% 0.003769 113% 0.003776 0.003792 114% 0.003805 117% 0.003810 0.003798 114% 0.003840 117% 2) 0.003666 94% 0.003577 94% 0.003632 0.003644 0.003614 0.003638 0.003652 0.003632 0.003661 0.003660 0.003658 revset: (-5000:-1000) and heads(-10000:-1) plain min max first last reverse rev..rst rev..ast sort sor..rst sor..ast 0) 0.004244 0.003368 0.003313 0.003367 0.003327 0.004325 0.003401 0.003379 0.004310 0.003359 0.003396 1) 0.003969 93% 0.003862 114% 0.003834 115% 0.003810 113% 0.003822 114% 0.003940 91% 0.003908 114% 0.003814 112% 0.003986 92% 0.003954 117% 0.003816 112% 2) 0.003728 93% 0.003638 94% 0.003659 0.003685 0.003628 94% 0.003716 94% 0.003653 93% 0.003655 0.003748 94% 0.003740 94% 0.003686 revset: heads(matching(tip, "author")) plain min max first last reverse rev..rst rev..ast sort sor..rst sor..ast 0) 7.574666 7.545950 7.570743 7.578697 7.525725 7.509929 7.443854 7.488442 7.452880 7.445411 7.689107 1) 7.549390 7.389162 7.529790 7.536297 7.450467 7.555347 7.404586 7.514948 7.542794 7.524787 7.536918 2) 7.568294 7.479326 7.578624 7.380375 7.440102 7.454218 7.515189 7.556511 7.524585 7.537566 7.507418 revset: heads(matching(tip, "author")) and -10000:-1 plain min max first last reverse rev..rst rev..ast sort sor..rst sor..ast 0) 7.512533 7.605877 7.382894 7.462109 7.420086 7.575034 7.448452 7.549374 7.457880 7.450308 7.515019 1) 7.548677 7.551832 7.629598 7.494857 7.550554 7.521838 7.451794 error 7.321781 7.546885 7.557523 2) 7.451985 7.541044 7.506563 7.470928 7.512618 7.474988 7.498887 7.547930 7.560276 7.618599 7.465442 revset: (-10000:-1) and heads(matching(tip, "author")) plain min max first last reverse rev..rst rev..ast sort sor..rst sor..ast 0) 7.465419 7.570089 7.439594 7.521221 7.498716 7.492922 7.479108 7.552397 7.407888 error 7.468264 1) 7.539866 7.548045 7.491761 7.517170 7.469824 7.501990 7.579102 7.502568 7.578102 7.555754 7.567622 2) 7.370463 7.514712 7.497024 7.679428 7.638138 7.490775 7.472273 7.652587 7.584139 7.511893 7.466384