Vladimir Kuzmin
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c12b185a6e
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cmd/compile: avoid mapaccess at m[k]=append(m[k]..
Currently rvalue m[k] is transformed during walk into:
tmp1 := *mapaccess(m, k)
tmp2 := append(tmp1, ...)
*mapassign(m, k) = tmp2
However, this is suboptimal, as we could instead produce just:
tmp := mapassign(m, k)
*tmp := append(*tmp, ...)
Optimization is possible only if during Order it may tell that m[k] is
exactly the same at left and right part of assignment. It doesn't work:
1) m[f(k)] = append(m[f(k)], ...)
2) sink, m[k] = sink, append(m[k]...)
3) m[k] = append(..., m[k],...)
Benchmark:
name old time/op new time/op delta
MapAppendAssign/Int32/256-8 33.5ns ± 3% 22.4ns ±10% -33.24% (p=0.000 n=16+18)
MapAppendAssign/Int32/65536-8 68.2ns ± 6% 48.5ns ±29% -28.90% (p=0.000 n=20+20)
MapAppendAssign/Int64/256-8 34.3ns ± 4% 23.3ns ± 5% -32.23% (p=0.000 n=17+18)
MapAppendAssign/Int64/65536-8 65.9ns ± 7% 61.2ns ±19% -7.06% (p=0.002 n=18+20)
MapAppendAssign/Str/256-8 116ns ±12% 79ns ±16% -31.70% (p=0.000 n=20+19)
MapAppendAssign/Str/65536-8 134ns ±15% 111ns ±45% -16.95% (p=0.000 n=19+20)
name old alloc/op new alloc/op delta
MapAppendAssign/Int32/256-8 47.0B ± 0% 46.0B ± 0% -2.13% (p=0.000 n=19+18)
MapAppendAssign/Int32/65536-8 27.0B ± 0% 20.7B ±30% -23.33% (p=0.000 n=20+20)
MapAppendAssign/Int64/256-8 47.0B ± 0% 46.0B ± 0% -2.13% (p=0.000 n=20+17)
MapAppendAssign/Int64/65536-8 27.0B ± 0% 27.0B ± 0% ~ (all equal)
MapAppendAssign/Str/256-8 94.0B ± 0% 78.0B ± 0% -17.02% (p=0.000 n=20+16)
MapAppendAssign/Str/65536-8 54.0B ± 0% 54.0B ± 0% ~ (all equal)
Fixes #24364
Updates #5147
Change-Id: Id257d052b75b9a445b4885dc571bf06ce6f6b409
Reviewed-on: https://go-review.googlesource.com/100838
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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2018-03-20 01:47:07 +00:00 |
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