Use broadcast for some operations in arraymath

[andreasnoack]

@nanosoldier runbenchmarks(ALL, vs = ":master")

[nanosoldier]

Your benchmark job has completed - possible performance regressions were detected. A full report can be found here. cc @jrevels

[andreasnoack]

Couldn't reproduce the regressions locally so will assume that they are noise.

[pabloferz]

For small arrays there's going to be a tiny overhead for things like broadcast!(conj, A, A) compared to conj!(A) since we make sure that the shapes of the arrays are compatible. We should probably have a non-size-checking broadcast! version.

[andreasnoack]

Decided to use map instead since it appears to be a bit faster for small arrays. Also realized that the binary operations could use map broadcast.

Update: Surprisingly, broadcast appears to be significantly faster than map. I can reproduce this locally. Would be good to know why.

[andreasnoack]

@nanosoldier runbenchmarks(ALL, vs = ":master")

[nanosoldier]

Your benchmark job has completed - possible performance regressions were detected. A full report can be found here. cc @jrevels

[andreasnoack]

@nanosoldier runbenchmarks("linalg", vs = ":master")

[nanosoldier]

Your benchmark job has completed - no performance regressions were detected. A full report can be found here. cc @jrevels

[KristofferC]

What changed from the previous nanosoldier run?

[andreasnoack]

map -> broadcast. I thought that map would be faster because it is simpler but for some reason broadcast is much faster. We should probably try to figure out why map is slower.

[andreasnoack]

Anybody knows what this test failure is https://travis-ci.org/JuliaLang/julia/jobs/187453412#L1598?

[Sacha0]

Referencing #17321 re. the map versus broadcast perf issue. Best!

[tkelman]

If someone restarted the travis job here, please back up the raw log to a gist before you do that next time. Restarting Travis overwrittes the logs and we would have lost the julia: /home/travis/build/JuliaLang/julia/deps/srccache/llvm-3.7.1/lib/MC/MCAsmStreamer.cpp:308: virtual void {anonymous}::MCAsmStreamer::EmitLabel(llvm::MCSymbol*): Assertion `Symbol->isUndefined() && "Cannot define a symbol twice!"' failed. error.

[tkelman]

there's a problem in the test system right now that isn't correctly failing builds when run in parallel. that assertion failure looks real.