golang/go

cmd/compile: unnecessary bounds check when slicing after using `slices.Grow`

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#73,145 建立於 2025年4月3日

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BugReportNeedsInvestigationPerformancecompiler/runtimehelp wanted

描述

Go version

go version go1.24.1 linux/amd64

Output of go env in your module/workspace:

-

What did you do?

package pkg

import "slices"

func Foo() {
	var xs []int
	xs = slices.Grow(xs, 4)[:len(xs)+4]
}

What did you see happen?

Slicing after growing inserts a check for the capacity and a conditional call to runtime.panicSliceAcap

What did you expect to see?

The compiler should be able to tell that we just guaranteed that the slice's capacity is at least len(xs)+4 and shouldn't insert another check.

貢獻者指南

技術棧
go
領域
backendperformance
議題類型
performance
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
4
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
half day
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
fresh
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
Go compiler internalsSSA prove passbounds check elimination
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
30
研究方向
Examine the prove pass in cmd/compile/internal/ssa/prove.go to understand how capacity checks are eliminated. Look for existing rules that prove slice capacity after built in functions like append. Implement a new rule that recognizes the pattern 'slices.Grow(s, n)[:len(s)+n]' and ensures the capacity is at least len(s)+n. Check existing linked issues or CLs for similar optimizations.