llvm/llvm-project

[DWARF] Line 0 should not have is_stmt set

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#33,870 创建于 2017年9月7日

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bugzilladebuginfogood first issuellvm:codegen

描述
Bugzilla Link 34522
Version trunk
OS Windows NT
CC @adrian-prantl,@dwblaikie

Extended Description

I think it does not make sense for a line-0 record to have is_stmt set. I made a point of turning it off for implicit line-0 records generated by DwarfDebug, and in real code I don't think we would ever see it.

However, adding an assertion to this effect broke 40 LLVM tests. In most cases, the problem is merely that the test-input IR does not specify everything that normal IR input has. In particular, at some point DISubprogram started making a distinction between Line and scopeLine, i.e. line of declaration versus where-the-code-starts. If the scopeLine argument is missing from textual IR, it defaults to zero, and that gets propagated to the entry point of the subprogram, which is a stopping point and therefore has is_stmt=1.

Defaulting scopeLine to Line fixed 33 of the tests, and eyeballing the other 7 suggests that most of them don't set Line either. This is (IMO) a matter of flawed tests and it should be no sweat to fix.

There is one test related to prologue-end that seems to be testing that it's okay for prologue-end to be line 0, and I ran out of time to investigate any further.

贡献者指南

技术栈
cpp
领域
backend
议题类型
bug
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。
1-2 days
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。
mostly clear
前置要求
DWARF formatLLVM debug infoC++test infrastructure
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。
30
研究方向
The issue explains that line 0 should not have is stmt set, and the author already turned it off for implicit records in DwarfDebug. The remaining work is to update the 7 tests that still fail, especially the prologue end test. Investigate the prologue end test to understand why it expects line 0 with is stmt and whether that needs a different fix. Also ensure that the scopeLine defaulting to Line is correctly implemented in the textual IR parsing. The relevant files are likely DwarfDebug.cpp and the test files in test/DebugInfo/.