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I also tried my hand at this guy for Gold, and got
// ILP of 5⅓, mostly because of the silly load latency :P. F("parseval") %str; load(%str, 0, b) %l0, load(%str, 1, b) %l1, // I'd fill this with loads if the two loops had the load(%str, 2, b) %l2; // same cycle length, but alas they do not. eqlb(%l0, 45) %neg, addp(%str, 1, b) %strplus1, pick(%neg, %strplus1, %str) %start, pick(%neg, %l1, %l0) %L0, pick(%neg, %l2, %l1) %L1; // Now we can finally start doing fun stuff. rd(b(0)) %zero, load(%start, 2, b) %char, // Not loading early means we take a stall in hexmode, eqlb(%L0, 48) %L00, // but loading early means decimalmode gets early loads. :( eqlb(%L1, 120) %L1x, addp(%start, 2) %startplus2, pick(%L00, %L1x, %L00) %hexmode, innertr(%hexmode, "parseval$hexmode", %zero, %startplus2, %neg), inner(%decimalmode, "parseval$decimalmode", %zero, %startplus2, %L1, %L0, %neg); // ILP of 9! Cycle length equals loop-caried dependency. L("parseval$hexmode") %total %str %neg; // a wild %char appears, right on time! load (%str, b, 2) %char, // Ideally this load would be fetching further ahead, gequ (%char, 48) %digitlo, // but we want one byte every 2 cycles, whereas the lequ (%char, 57) %digithi, // other branch want one every 3 cycles, so you can't gequ (%char, 97) %letterlo, // hoist the setup into the header. lequ (%char, 102) %letterhi, sub (%char, 48) %digitval, sub (%char, 87) %letterval, shiftl(%total, 4) %shifttot, addp (%str, 1, b) %newstr, pick (%digitlo, %digithi, %digitlo) %digit, pick (%letterlo, %letterhi, %letterlo) %letter; orl (%digit, %letter) %inrange, add (%shifttot, %digitval) %digittot, add (%shifttot, %letterval) %lettertot, pick (%digit, %digittot, %lettertot) %newtotal, conform(%newtotal, %newstr, %neg, %total, %char), leavefl(%inrange, "parseval$finish", %total, %char, %neg), br("parseval$hexmode"); // ILP of only 4⅓. Cycle length equals loop-caried dependency. // Not much one can do when the multiply is slow... :( L("parseval$decimalmode") %total %str %newchar %char %neg; // A wild %newnewchar appears... six cycles early. // That's pretty lame, but fixing it take a branch. load (%str, b, 3) %newnewchar, gequ (%char, 48) %digitlo, lequ (%char, 57) %digithi, addp (%str, 1, b) %newstr, sub (%char, 48) %digitval, shiftl(%total, 1) %totalx2, shiftl(%total, 3) %totalx8, pick (%digitlo, %digithi, %digitlo) %digit, leavefl(%digit, "parseval$finish", %total, %char, %neg); // This is a very sad instruction. add (%totalx2, %totalx8) %totalx10; add (%totalx10, %digitval) %newtotal, rescue(%newtotal, %newstr, %newnewchar, %newchar, %neg), br("parseval$hexmode"); // ILP of 4½. Meh, it works. L("parseval$finish") %total %char %neg; // a wild %fakechar appears eqlb(%char, 75) %K, eqlb(%char, 77) %M, neg(%total) %negtotal, pick(%neg, %negtotal, %total) %totalsigned; shiftl(%totalsigned, 10) %totalK, shiftl(%totalsigned, 20) %totalM, pick(%K, %totalK, %totalsigned) %totalelse, retntr(%M, %totalM), retn(%totalelse);Interesting architecture indeed. I’ve not handled the busywork belt numbers, but I’ve checked they’re in a consistent position. I expect one’s better off having a branch before entering either loop where you flood it with correctly-delayed loads ahead of time; that way you don’t risk stalls in the loop itself, but it adds a cycle (and a jump) to every call to parseval. Delayed loads don’t work because the loop count is different, and tagged loads don’t work because they don’t pipeline.
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This reply was modified 7 years, 6 months ago by
Veedrac.
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This reply was modified 7 years, 6 months ago by
The letter-number pairs are the slots, and the arrows are the phase (reader ↥, compute ▸, call ↱, pick ?, writer ↧, conform =, transfer ↦). The symbol choice is from http://millcomputing.com/instructions.html, with the phase column collapsed.
Though if I had my say it’d be reader ⤒, compute ⏩, call ↺, writer ↧, conform ♺, transfer ⤷.
I imagine you would do something like
add b0, b1 pick cond, b0, None add b0, 1“None” effectively absorbs all computation without error. So you would have:
[12, 11, cond=1, ...] [23, 12, 11, cond=1, ...] (add b0, b1) [23, 23, 12, 11, cond=1, ...] (pick cond, b0, None) [24, 23, 23, 12, 11, cond=1, ...] (add b0, 1)or
[12, 11, cond=0, ...] [23, 12, 11, cond=0, ...] (add b0, b1) [None, 23, 12, 11, cond=0, ...] (pick cond, b0, None) [None, None, 23, 12, 11, cond=0, ...] (add b0, 1)It’s not obvious how to turn None into its value, though. You could do
add b0, b1 # store pick cond, b0, None add b0, 1 # store (may do nothing) # loadbut that seems like a lot of overhead to do very little.
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Obviously, though, in this case the best option is just
add b0, b1 add b0, cond🙂
