That's some interesting insight - thanks Florian. Something that might need rigorous timing tests in that case. I thought about the binary search map since the case statements jump to a procedure call, and I wondered if I could take advantage of that homogenuity. In the meantime, I found a couple of peephole optimisations that don't rely on tricky code like that in the bug report! I'll submit a patch later, just in case I find a few more.
Gareth aka Kit. On Sun 27/05/18 13:00 , Florian Klämpfl flor...@freepascal.org sent: Am 27.05.2018 um 02:48 schrieb J. Gareth Moreton: > Hi guys, > > So I'm still experimenting and researching with the deep optimiser, and I'm starting to have some > successes... until I found a compiler bug! > > https://bugs.freepascal.org/view.php?id=33794 [1] > > What I'm trying to do, and something which I'd like to try out with the regular peephole optimiser > at some point, is using a sorted list that maps an assembler command to a handler procedure and > using a binary search to find the correct routine. This will speed up the optimiser from O(n) (i.e. > the speed of "case X of") to O(log n) per line of code, FPC knows different means to generate code for case statements (linear list, jump table, jump tree); based on a heuristics the method is chosen. If in case of the assembler optimizer, FPC chooses the wrong approach, this heuristics should be checked, see e.g. compiler/ncgset.pas:1170+: { value has been determined on an i7-4770 using a random case with random values if more values are known, this can be handled depending on the target CPU Testing on a Core 2 Duo E6850 as well as on a Raspi3 showed also, that 64 is a good value } else if labelcnt>=64 then genjmptree(labels) else genlinearlist(labels); The label count if a jmp tree is beneficial, is surprisingly high, probably due to branch prediction which breaks completely havoc in case of a jump tree. _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org [2] http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel [3]">http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel Links: ------ [1] https://bugs.freepascal.org/view.php?id=33794 [2] mailto:fpc-devel@lists.freepascal.org [3] http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
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