b1785a5065
This adds a heap-based proper priority queue to the scheduler which made a relatively easy to test quite a few heuristics that "ought to work well". For go tools themselves (which may not be representative) the heuristic that works best is (1) in line-number-order, then (2) from more to fewer args, then (3) in variable ID order. Trying to improve this with information about use at end of blocks turned out to be fruitless -- all of my naive attempts at using that information turned out worse than ignoring it. I can confirm that the stores-early heuristic tends to help; removing it makes the results slightly worse. My metric is code size reduction, which I take to mean fewer spills from register allocation. It's not uniform. Here's the endpoints for "vet" from one set of pretty-good heuristics (this is representative at least). -2208 time.parse 13472 15680 -14.081633% -1514 runtime.pclntab 1002058 1003572 -0.150861% -352 time.Time.AppendFormat 9952 10304 -3.416149% -112 runtime.runGCProg 1984 2096 -5.343511% -64 regexp/syntax.(*parser).factor 7264 7328 -0.873362% -44 go.string.alldata 238630 238674 -0.018435% 48 math/big.(*Float).round 1376 1328 3.614458% 48 text/tabwriter.(*Writer).writeLines 1232 1184 4.054054% 48 math/big.shr 832 784 6.122449% 88 go.func.* 75174 75086 0.117199% 96 time.Date 1968 1872 5.128205% Overall there appears to be an 0.1% decrease in text size. No timings yet, and given the distribution of size reductions it might make sense to wait on those. addr2line text (code) = -4392 bytes (-0.156273%) api text (code) = -5502 bytes (-0.147644%) asm text (code) = -5254 bytes (-0.187810%) cgo text (code) = -4886 bytes (-0.148846%) compile text (code) = -1577 bytes (-0.019346%) * changed cover text (code) = -5236 bytes (-0.137992%) dist text (code) = -5015 bytes (-0.167829%) doc text (code) = -5180 bytes (-0.182121%) fix text (code) = -5000 bytes (-0.215148%) link text (code) = -5092 bytes (-0.152712%) newlink text (code) = -5204 bytes (-0.196986%) nm text (code) = -4398 bytes (-0.156018%) objdump text (code) = -4582 bytes (-0.155046%) pack text (code) = -4503 bytes (-0.294287%) pprof text (code) = -6314 bytes (-0.085177%) trace text (code) = -5856 bytes (-0.097818%) vet text (code) = -5696 bytes (-0.117334%) yacc text (code) = -4971 bytes (-0.213817%) This leaves me sorely tempted to look into a "real" scheduler to try to do a better job, but I think it might make more sense to look into getting loop information into the register allocator instead. Fixes #14577. Change-Id: I5238b83284ce76dea1eb94084a8cd47277db6827 Reviewed-on: https://go-review.googlesource.com/20240 Run-TryBot: David Chase <drchase@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>
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