[all-commits] [llvm/llvm-project] 1956cf: [lldb/DWARF] Don't treat class declarations with c...

[Pavel Labath via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 1956cf1042d3c406d9e9cefe47d3b43adf2bdbe1
      https://github.com/llvm/llvm-project/commit/1956cf1042d3c406d9e9cefe47d3b43adf2bdbe1
  Author: Pavel Labath <pavel at labath.sk>
  Date:   2020-07-27 (Mon, 27 Jul 2020)

  Changed paths:
    M lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
    M lldb/test/API/functionalities/limit-debug-info/TestLimitDebugInfo.py
    M lldb/test/API/functionalities/limit-debug-info/main.cpp
    M lldb/test/API/functionalities/limit-debug-info/one.cpp
    M lldb/test/API/functionalities/limit-debug-info/onetwo.h
    M lldb/test/API/functionalities/limit-debug-info/two.cpp
    A lldb/test/Shell/SymbolFile/DWARF/DW_AT_declaration-with-children.s

  Log Message:
  -----------
  [lldb/DWARF] Don't treat class declarations with children as definitions

Summary:
This effectively reverts r188124, which added code to handle
(DW_AT_)declarations of structures with some kinds of children as
definitions. The commit message claims this is a workaround for some
kind of debug info produced by gcc. However, it does not go into
specifics, so it's hard to reproduce or verify that this is indeed still a
problem.

Having this code is definitely a problem though, because it mistakenly
declares incomplete dwarf declarations to be complete. Both clang (with
-flimit-debug-info) and gcc (by default) generate DW_AT_declarations of
structs with children. This happens when full debug info for a class is
not emitted in a given compile unit (e.g. because of vtable homing), but
the class has inline methods which are used in the given compile unit.
In that case, the compilers emit a DW_AT_declaration of a class, but
add a DW_TAG_subprogram child to it to describe the inlined instance of
the method.

Even though the class tag has some children, it definitely does not
contain enough information to construct a full class definition (most
notably, it lacks any members). Keeping the class as incomplete allows
us to search for a real definition in other modules, helping the
-flimit-debug-info flow. And in case the definition is not found we can
display a error message saying that, instead of just showing an empty
struct.

Reviewers: clayborg, aprantl, JDevlieghere, shafik

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D83302