On Tue, Mar 31, 2020 at 2:31 AM Andres Freund <and...@anarazel.de> wrote: > > Hi, > > On 2020-03-30 21:33:14 +0800, John Naylor wrote: > > Then I used the attached program to measure various combinations of > > compiled instructions using two constant multipliers iterating over > > bytes similar to a generated hash function. > > It looks like you didn't attach the program?
Funny, I did, but then decided to rename the files. Here they are. I tried to make the loop similar to how it'd be in the actual hash function, but leaving out the post-loop modulus and array access. Each loop iteration is dependent on the last one's result. > It's a bit complicated by the fact that there's more execution ports to > execute shift/add than there ports to compute some form of leas. And > some of that won't easily be measurable in a micro-benchmark, because > there'll be dependencies between the instruction preventing any > instruction level parallelism. > > I think the form of lea generated here is among the ones that can only > be executed on port 1. Whereas e.g. an register+register/immediate add > can be executed on four different ports. That's interesting, I'll have to look into that. Thanks for the info! -- John Naylor https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
test-const-mult.c
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test-const-mult-2.c
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