cmd/compile: Fannkuch benchmark performance regression #27108
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/cc @randall77 |
Disabling branchelim seems to bring performance back to 1.10 level. Interestingly enough, on test/bench/go1/fannkuch disabling CMOV hurts performance by 20% |
I've looked at instruction-level profile and found that all conditional moves are out of the hot-spot. Main problem is that enabling branchelim pass caused different register allocation, which in turn put register spills/fills inside the inner loop. |
Punting to 1.13, too late for anything major in 1.12. |
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Please answer these questions before submitting your issue. Thanks!
What version of Go are you using (
go version
)?go version go1.11rc1 darwin/amd64
Does this issue reproduce with the latest release?
No.
What operating system and processor architecture are you using (
go env
)?macOS 10.13.6 (darwin/amd64)
What did you do?
tested the benchmark at:
https://benchmarksgame-team.pages.debian.net/benchmarksgame/program/fannkuchredux-go-1.html
using 1.10.3 and 1.11rc1 with:
time go run fannkuchredux.go 12
time go1.11rc1 run fannkuchredux.go 12
results:
1.10.3: go run fannkuchredux.go 12 44.65s user 0.21s system 372% cpu 12.033 total
1.11rc1: go1.11rc1 run fannkuchredux.go 12 57.70s user 0.24s system 373% cpu 15.528 total
What did you expect to see?
1.11rc1 timings closer to 1.10.3
What did you see instead?
1.11rc1 timings slower than 1.10.3
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