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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>
108 lines
2.8 KiB
Go
108 lines
2.8 KiB
Go
// errorcheck -0 -m -l
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Test escape analysis for maps.
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package escape
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var sink interface{}
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func map0() {
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m := make(map[*int]*int) // ERROR "make\(map\[\*int\]\*int\) does not escape"
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// BAD: i should not escape
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i := 0 // ERROR "moved to heap: i"
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// BAD: j should not escape
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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_ = m
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}
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func map1() *int {
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m := make(map[*int]*int) // ERROR "make\(map\[\*int\]\*int\) does not escape"
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// BAD: i should not escape
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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return m[&i]
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}
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func map2() map[*int]*int {
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m := make(map[*int]*int) // ERROR "make\(map\[\*int\]\*int\) escapes to heap"
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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return m
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}
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func map3() []*int {
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m := make(map[*int]*int) // ERROR "make\(map\[\*int\]\*int\) does not escape"
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i := 0 // ERROR "moved to heap: i"
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// BAD: j should not escape
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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var r []*int
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for k := range m {
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r = append(r, k) // ERROR "append escapes to heap"
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}
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return r
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}
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func map4() []*int {
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m := make(map[*int]*int) // ERROR "make\(map\[\*int\]\*int\) does not escape"
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// BAD: i should not escape
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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var r []*int
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for k, v := range m {
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// We want to test exactly "for k, v := range m" rather than "for _, v := range m".
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// The following if is merely to use (but not leak) k.
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if k != nil {
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r = append(r, v) // ERROR "append escapes to heap"
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}
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}
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return r
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}
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func map5(m map[*int]*int) { // ERROR "m does not escape"
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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}
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func map6(m map[*int]*int) { // ERROR "m does not escape"
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if m != nil {
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m = make(map[*int]*int) // ERROR "make\(map\[\*int\]\*int\) does not escape"
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}
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m[&i] = &j
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}
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func map7() {
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// BAD: i should not escape
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i := 0 // ERROR "moved to heap: i"
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// BAD: j should not escape
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j := 0 // ERROR "moved to heap: j"
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m := map[*int]*int{&i: &j} // ERROR "map\[\*int\]\*int{...} does not escape"
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_ = m
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}
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func map8() {
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m := map[*int]*int{&i: &j} // ERROR "map\[\*int\]\*int{...} escapes to heap"
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sink = m
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}
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func map9() *int {
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// BAD: i should not escape
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i := 0 // ERROR "moved to heap: i"
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j := 0 // ERROR "moved to heap: j"
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m := map[*int]*int{&i: &j} // ERROR "map\[\*int\]\*int{...} does not escape"
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return m[nil]
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}
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