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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>
62 lines
1.7 KiB
Go
62 lines
1.7 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 function parameters.
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// In this test almost everything is BAD except the simplest cases
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// where input directly flows to output.
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package foo
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func f(buf []byte) []byte { // ERROR "leaking param: buf to result ~r0 level=0$"
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return buf
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}
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func g(*byte) string
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func h(e int) {
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var x [32]byte // ERROR "moved to heap: x$"
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g(&f(x[:])[0])
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}
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type Node struct {
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s string
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left, right *Node
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}
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func walk(np **Node) int { // ERROR "leaking param content: np"
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n := *np
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w := len(n.s)
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if n == nil {
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return 0
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}
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wl := walk(&n.left)
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wr := walk(&n.right)
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if wl < wr {
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n.left, n.right = n.right, n.left // ERROR "ignoring self-assignment"
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wl, wr = wr, wl
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}
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*np = n
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return w + wl + wr
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}
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// Test for bug where func var f used prototype's escape analysis results.
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func prototype(xyz []string) {} // ERROR "xyz does not escape"
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func bar() {
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var got [][]string
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f := prototype
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f = func(ss []string) { got = append(got, ss) } // ERROR "leaking param: ss" "func literal does not escape" "append escapes to heap"
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s := "string"
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f([]string{s}) // ERROR "\[\]string{...} escapes to heap"
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}
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func strmin(a, b, c string) string { // ERROR "leaking param: a to result ~r0 level=0" "leaking param: b to result ~r0 level=0" "leaking param: c to result ~r0 level=0"
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return min(a, b, c)
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}
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func strmax(a, b, c string) string { // ERROR "leaking param: a to result ~r0 level=0" "leaking param: b to result ~r0 level=0" "leaking param: c to result ~r0 level=0"
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return max(a, b, c)
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}
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