[PATCH] D58538: [DebugInfo] Add source attributes for function declaration on behalf of owner CU

[Eugene Leviant via Phabricator via llvm-commits]

evgeny777 created this revision.
evgeny777 added reviewers: pcc, dblaikie, dexonsmith, chandlerc.
Herald added subscribers: jdoerfert, aprantl, mehdi_amini.

There seems to be a bug in DwarfUnit which one can easily step on when building boost examples with full LTO.
It causes template function declaration inside a class to have invalid `DW_AT_decl_file` attribute and GNU 
objdump and addr2line tools to report multiple failures while processing such executables.

Assume we have following C++ structure:

  struct S {
    int foo;
    template< class T > T squared(T value) { return value * value; }
  };

Even though this structure contains two elements, debug information for it will contain only one,
because `squared` may not be used anywhere in the program and so may not even be compiled.

  !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, ....)
  !18 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "S", ...., elements !19, ....)
  !19 = !{!20}
  !20 = !DIDerivedType(tag: DW_TAG_member, name: "foo", ....)

If some CU in a program is using S::squared two records will be added to debug information: definition and declaration
The latter will reference `struct S` via `scope field`:

  !37 = distinct !DISubprogram(name: "squared<int>", unit !2, declaration !38, .....)
  !38 = distinct !DISubprogram(name: "squared<int>", scope !18, ....)

The `struct S` could be used in multiple CUs, some of them may use `squared` and some may not. When full LTO is used
IRMover will combine debug information from all CUs merging the types and DIE corresponding to declaration of `squared`
my be processed by DwarfUnit instance corresponding to CU#1 and DIE corresponding to its scope (struct S) may be owned 
by CU#2. In such case if we add source line attributes for declaration on behalf of CU#1 we'll likely break the debug info, 
because file ids in CU#1 and CU#2 don't match.

This patch fixes the issue by adding debug info for declaration on behalf of owning CU.


https://reviews.llvm.org/D58538

Files:
  include/llvm/CodeGen/DIE.h
  lib/CodeGen/AsmPrinter/DIE.cpp
  lib/CodeGen/AsmPrinter/DwarfUnit.cpp
  test/DebugInfo/X86/template_function_decl.ll

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