swiftlang/swift

[SR-1111] Non-optimized builds should avoid redundant thick_to_objc_metatype conversions

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#43,724 创建于 2016年3月30日

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IRGencompilergood first issueimprovementnon-optimized only

描述
Previous ID SR-1111
Radar None
Original Reporter @belkadan
Type Improvement
Votes 0
Component/s Compiler
Labels Improvement, IRGen, NotOptimizedOnly, StarterBug
Assignee None
Priority Medium

md5: ee5fa37243b2596a51a6125675863696

Issue Description:

In this code:

import Foundation
func test() -> Bool {
  let a = RunLoop.current
  let b = RunLoop.main
  return a === b
}

We're smart enough to avoid emitting two references to the metadata for NSRunLoop, but not smart enough (in -Onone builds) to avoid emitting the conversion to an ObjC Class twice, which involves a branch. We should be able to reuse the value from the first thick_to_objc_metatype conversion.

贡献者指南

技术栈
swift
领域
performance
议题类型
feature
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
half day
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
Swift compiler internalsIRGenthick to objc metatype concept
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
35
研究方向
The issue involves reusing the result of thick to objc metatype conversion in non optimized builds. The relevant code is likely in the IRGen component of the Swift compiler. A contributor should search for where thick to objc metatype is emitted and check if redundant conversions are avoided. Given the issue is old, verify if this improvement is already implemented or still relevant.