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ce88e341b9
When appending, if the backing store doesn't escape and a
constant-sized backing store is big enough, use a constant-sized
stack-allocated backing store instead of allocating it from the heap.
cmd/go is <0.1% bigger.
As an example of how this helps, if you edit strings/strings.go:FieldsFunc
to replace
spans := make([]span, 0, 32)
with
var spans []span
then this CL removes the first 2 allocations that are part of the growth sequence:
│ base │ exp │
│ allocs/op │ allocs/op vs base │
FieldsFunc/ASCII/16-24 3.000 ± ∞ ¹ 2.000 ± ∞ ¹ -33.33% (p=0.008 n=5)
FieldsFunc/ASCII/256-24 7.000 ± ∞ ¹ 5.000 ± ∞ ¹ -28.57% (p=0.008 n=5)
FieldsFunc/ASCII/4096-24 11.000 ± ∞ ¹ 9.000 ± ∞ ¹ -18.18% (p=0.008 n=5)
FieldsFunc/ASCII/65536-24 18.00 ± ∞ ¹ 16.00 ± ∞ ¹ -11.11% (p=0.008 n=5)
FieldsFunc/ASCII/1048576-24 30.00 ± ∞ ¹ 28.00 ± ∞ ¹ -6.67% (p=0.008 n=5)
FieldsFunc/Mixed/16-24 2.000 ± ∞ ¹ 2.000 ± ∞ ¹ ~ (p=1.000 n=5)
FieldsFunc/Mixed/256-24 7.000 ± ∞ ¹ 5.000 ± ∞ ¹ -28.57% (p=0.008 n=5)
FieldsFunc/Mixed/4096-24 11.000 ± ∞ ¹ 9.000 ± ∞ ¹ -18.18% (p=0.008 n=5)
FieldsFunc/Mixed/65536-24 18.00 ± ∞ ¹ 16.00 ± ∞ ¹ -11.11% (p=0.008 n=5)
FieldsFunc/Mixed/1048576-24 30.00 ± ∞ ¹ 28.00 ± ∞ ¹ -6.67% (p=0.008 n=5)
(Of course, people have spotted and fixed a bunch of allocation sites
like this, but now we're ~automatically doing it everywhere going forward.)
No significant increases in frame sizes in cmd/go.
Change-Id: I301c4d9676667eacdae0058960321041d173751a
Reviewed-on: https://go-review.googlesource.com/c/go/+/664299
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
2.8 KiB
2.8 KiB