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Groups > comp.lang.java.programmer > #36867
| From | Martin Gregorie <martin@address-in-sig.invalid> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: One code is aggressively optimised, while another not. Why? |
| Date | 2017-07-12 17:04 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <ok5kr7$q3o$2@dont-email.me> (permalink) |
| References | <87lgnu5b9o.fsf@munus.decebal.nl> <ok5auj$3m4$1@dont-email.me> |
On Wed, 12 Jul 2017 09:19:36 -0500, Joshua Cranmer 🐧 wrote: > I don't know your quality of microbenchmark suite, but a result that > takes around a thousand clock cycles or so strongly suggests that the > optimizer did loop idiom detection to replace the loop with sum = > f(start, end). That the second loop didn't suggests either that the loop > didn't tickle the loop idiom detector or that it bailed on computing the > result do to an overflow. Since my development computer is currently > nonfunctional, I can't do any more detailed analysis. > Or possibly the optimiser knows a fast way to add long to long but not to add int to long. Alternatively, the compiler may do mixed length integer addition by extending the shorter representation and then adding two integers of the same length and possibly the optimiser can't do a lot to speed that up. -- martin@ | Martin Gregorie gregorie. | Essex, UK org |
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One code is aggressively optimised, while another not. Why? Cecil Westerhof <Cecil@decebal.nl> - 2017-07-12 10:07 +0200
Re: One code is aggressively optimised, while another not. Why? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-07-12 09:38 -0400
Re: One code is aggressively optimised, while another not. Why? Cecil Westerhof <Cecil@decebal.nl> - 2017-07-13 09:51 +0200
Re: One code is aggressively optimised, while another not. Why? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-07-13 11:05 -0400
Re: One code is aggressively optimised, while another not. Why? Cecil Westerhof <Cecil@decebal.nl> - 2017-07-13 18:52 +0200
Re: One code is aggressively optimised, while another not. Why? Cecil Westerhof <Cecil@decebal.nl> - 2017-07-13 19:51 +0200
Re: One code is aggressively optimised, while another not. Why? Joshua Cranmer 🐧 <Pidgeot18@verizon.invalid> - 2017-07-12 09:19 -0500
Re: One code is aggressively optimised, while another not. Why? Martin Gregorie <martin@address-in-sig.invalid> - 2017-07-12 17:04 +0000
Re: One code is aggressively optimised, while another not. Why? Arne Vajhøj <arne@vajhoej.dk> - 2017-07-12 21:02 -0400
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