[Lldb-commits] [PATCH] D138834: [lldb] Fix simple template names interaction with debug info declarations

[Arthur Eubanks via Phabricator via lldb-commits]

aeubanks added inline comments.


================
Comment at: lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp:765
+        m_ast.CreateClassTemplateSpecializationType(class_specialization_decl);
+    return clang_type.GetTypeName(/*BaseOnly*/ true);
+  }
----------------
Michael137 wrote:
> Michael137 wrote:
> > Ok so what we're doing is:
> > 1. Create a `ClassTemplateSpecializationDecl` with an empty basename
> > 2. Return the type-name and since the basename is empty we end up with just the template arguments
> > 
> > Why can't we just call `GetTemplateParametersString(die)` instead of creating this function?
> Can confirm that this works locally. Though required moving that function out of the DWARFASTParserClang, which seems OK
`GetTemplateParametersString` is specifically only used for `GetCPlusPlusQualifiedName`, which is used below
```
      // For C++, we rely solely upon the one definition rule that says
      // only one thing can exist at a given decl context. We ignore the
      // file and line that things are declared on.
      std::string qualified_name = GetCPlusPlusQualifiedName(die);
```
so it doesn't have to match clang's printing. but for the simple template name stuff, we are comparing clang-generated names, so everything needs to go through clang.

I've replaced `GetTemplateParametersString` with this code that goes through clang as well


================
Comment at: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp:2988
+        template_params =
+            dwarf_ast->GetForwardDeclarationDIETemplateParams(die);
+    }
----------------
Michael137 wrote:
> So after this call we'll have an unnamed `ClassTemplateDecl` hanging off the AST? Doing this inside `FindDefinitionTypeForDWARFDeclContext` instead of `ParseStructureLikeDIE` feels a bit off. But will have to understand this change a bit deeper to know whether there is something we can do about that.
> 
> As a side-note, we seem to be accumulating a lot of blocks around LLDB that look like:
> ```
> // Do X because -gsimple-template-names
> if (name.contains('<')) {
>    // Do something
> }
> ```
> Still wonder if there isn't some flag that can be set on, e.g., a CU, that would tell us this.
the effect is not really per-CU but rather per-DIE because in some cases (where DWARF roundtripping is lossy, @dblaikie would know best) we still put template params in the name. so it needs to be checked per-DIE

I agree that it's weird to create clang AST nodes here and then forget about them, but clang uses a bump allocator and we can't easily delete it. As long as we call this at most once or twice per DIE, I don't think it's worth caching the results, but if we do end up using this more, we do need to cache the created AST nodes. I've added a comment to the docstring.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D138834/new/

https://reviews.llvm.org/D138834