stable layout bug for imported record decls.

Hi clang-dev, lldb-dev,

It looks like my clang commit r305850, which modified ASTImporter to import method override tables from an external context, introduced a new bug which manifests as incorrect vtable layouts for LLDB expression code.

The bug itself is fairly straightforward. In r305850 I introduced the following method, which is called from ASTNodeImporter::VisitFunctionDecl:

void ASTNodeImporter::ImportOverrides(CXXMethodDecl *ToMethod,
CXXMethodDecl *FromMethod) {
for (auto FromOverriddenMethod : FromMethod->overridden_methods())
ToMethod->addOverriddenMethod(
cast(Importer.Import(const_cast<CXXMethodDecl
>(
FromOverriddenMethod))));
}

This will produce the correct override table, but can also cause methods in the Base class to be visited in the wrong order. Consider:

class Base {
public:
virtual void bar() {}
virtual void foo() {}
};

class Derived : public Base {
public:
void foo() override {}
};

If Derived is imported into a new context before Base, then the importer will visit Derived::foo, and (via ImportOverrides) immediately import Base::foo, but this happens before Base::bar is imported. As a consequence, the decl order on the imported Base class will end up being [ foo, bar ], instead of [ bar, foo ]. In LLDB expression evaluation this manifests as an incorrect vtable layout for Base, with foo occupying the first slot.

I am looking for suggestions on the right way to fix this. A brute force solution might be to always have ASTNodeImporter::VisitRecordDecl visit all base classes, then all virtual methods, which would ensure they are visited in the original decl order. However I do not know whether this covers all paths by which a CXXRecordDecl might be imported, nor whether the performance of this solution would be acceptable (it seems like it would preclude a lot of laziness).

Alternatively we might be able to associate an index with each imported decl and sort on that when we complete the type, but that would leave imported decls in the wrong order until the type was complete, and since I do not know all the use cases for the importer I’m concerned people may rely on the decl order before type is complete.

Any insight from ASTImporter experts would be greatly appreciated. :slight_smile:

Cheers,
Lang.

(+ Gabor and Gabor)

Hi Lang,

We faced a very similar issue with record fields where import order can change the order of imported FieldDecls resulting in broken ASTRecordLayout. The patch for this issue is on review: https://reviews.llvm.org/D44100. It just reorders the fields after structure import is finished. CSA guys also reported the same problem with FriendDecls in the same review.The order of methods was not a problem for us but your report adds a new item to support. It looks like _all_ decls inside RecordDecl have to be reordered. I'll try to resurrect the patch this weekend (it is a bit outdated due to my workload, sorry) and add you as a reviewer so you can check if it solves the problem or not.

09.08.2018 20:46, Lang Hames via lldb-dev пишет:

Hi Lang, Alexey,

I dug deeper into this and it seems like the issue happens only when a
**minimal** import is used. LLDB uses the minimal import. CrossTU
static analyzer uses the normal mode.
In normal import mode, in `ImportDeclContext` we do import all the
methods in the correct order. However, in minimal mode we early return
before importing the methods.
So by merging D44100 this particular problem will not be solved.
Still, that patch sounds very reasonable and I support that we should
reorder all imported Decls, not just fields.

One trivial solution would be to change `ImporDeclContext` to behave
the same way in both modes. This is somewhat similar to the "brute
force" method you mentioned.
I am not an LLDB expert, so I am not sure if this is acceptable, and
really don't know how many LLDB tests would it break, but this seems
the simplest solution (and preferred) to me.

The other solution if you'd like to keep the minimal behavior is the
index based solution (as you mentioned).
You should compare the order of all the imported methods (and fields)
to the order in the original class in the "From" context. And I
believe you have to do that at the end of VisitFunctionDecl. It would
not work if you did that check when the type become complete, since in
minimal mode we never set the class to be incomplete.

I have created a unit test case, which fails in minimal mode and
succeeds in normal mode. You can change the mode in
`ASTImporterTestBase::TU::lazyInitImporter`.
If you provide a patch then could you please also add this test (or
similar) for both normal and minimal mode?

TEST_P(ASTImporterTestBase, OrderOfVirtualMethods) {
  auto Code =
      R"(
      class Base {
      public:
        virtual void bar() {}
        virtual void foo() {}
      };

      class Derived : public Base {
      public:
        void foo() override {}
      };
      )";
  Decl *FromTU = getTuDecl(Code, Lang_CXX11, "input0.cc");
  auto *DerivedFoo = FirstDeclMatcher<FunctionDecl>().match(
      FromTU, functionDecl(hasName("foo"),
                           hasParent(cxxRecordDecl(hasName("Derived")))));
  auto *BaseBar = FirstDeclMatcher<FunctionDecl>().match(
      FromTU, functionDecl(hasName("bar"),
                           hasParent(cxxRecordDecl(hasName("Base")))));

  Import(DerivedFoo, Lang_CXX);
  // Importing Base::bar explicitly is needed only in minimal mode,
  // in normal mode we already imported all methods of Base.
  Import(BaseBar, Lang_CXX);

  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
  auto *ImportedBase = FirstDeclMatcher<CXXRecordDecl>().match(
      ToTU, cxxRecordDecl(hasName("Base")));
  MatchVerifier<Decl> Verifier;
  EXPECT_TRUE(Verifier.match(ImportedBase,
                             cxxRecordDecl(hasMethodOrder({"bar", "foo"}))));
}

Thanks,
Gabor

I have forgot to include the matcher I used for the test:

AST_MATCHER_P(CXXRecordDecl, hasMethodOrder, std::vector<StringRef>, Order) {
  size_t Index = 0;
  for (CXXMethodDecl *Method : Node.methods()) {
    if (!Method->isImplicit()) {
      if (Method->getName() != Order[Index])
        return false;
      ++Index;
    }
  }
  return Index == Order.size();
}

Gabor

Hi Alexey, Gábor,

Thank you so much for this information. This is very helpful!

One trivial solution would be to change ImporDeclContext to behave
the same way in both modes. This is somewhat similar to the “brute
force” method you mentioned.
I am not an LLDB expert, so I am not sure if this is acceptable, and
really don’t know how many LLDB tests would it break, but this seems
the simplest solution (and preferred) to me.

Sounds good to me. I will try this, see whether anything fails, and try to get a sense of the performance impact.

Do you know of anyone using minimal import mode other than LLDB?

Cheers,
Lang

Hi Lang,

There are only two users of ASTImporter known to me: CSA and LLDB. And CSA doesn't use minimal import.

13.08.2018 23:28, Lang Hames via lldb-dev пишет:

Hi Lang,

It might be interesting to consider how this is addressed by the ExternalASTSource interface. There, we have separate “import the lexical contents of this AST node (including populating the lexical declarations list with all members, in the right order)”, “import the lookup results for this name in this context (and cache them but don’t add them to the list of lexical members)” and “import this specific declaration member (but don’t add it to the list of lexical members)” queries. One could imagine doing something similar for the AST importer: when you’re performing a minimal import but you want to import a method declaration, don’t insert it into the list of lexical members of the enclosing record. Instead, defer doing that until a complete type is required (at that point, you’d need to import all the relevant members anyway, including the base classes and virtual functions in the right order).

The above approach would violate AST invariants (you’d have a declaration whose lexical parent doesn’t believe it lexically contains the child), but I don’t know off-hand whether that would be problematic. Perhaps a better approach would be to make the “minimal” mode for the ASTImporter provide an ExternalASTSource to lazily complete the AST as needed (thereby avoiding violating the invariant, because you would populate the lexical declarations list whenever anyone actually asks for it).

Hi Richard,

Perhaps a better approach would be to make the “minimal” mode for the ASTImporter provide an ExternalASTSource to lazily complete the AST as needed (thereby avoiding violating the invariant, because you would populate the lexical declarations list whenever anyone actually asks for it).

This seems worth investigating. I wonder if it might also fix another bug that I know of involving virtual methods with covariant return types. (You and I actually discussed it at one of the socials a while back, but I have not had time to dig into it further.)

The reproducer for the bug is:

class Foo {};
class Bar : public Foo {};

class Base {
public:
virtual Foo* foo() { return nullptr; }
};

class Derived : public Base {
public:
virtual Bar* foo() { return nullptr; }
};

int main() {
Derived D;
D.foo(); // Evaluate ‘D.foo()’ here, crash LLDB.
}

The issue is that since Bar’s definition is not used its bases are never imported, and so the call to Bar::bases() crashes in CodeGen. If we provided an ExternalASTSource, would that be able to lazily complete the bases?

Cheers,
Lang.

Hi Richard,

Perhaps a better approach would be to make the “minimal” mode for the ASTImporter provide an ExternalASTSource to lazily complete the AST as needed (thereby avoiding violating the invariant, because you would populate the lexical declarations list whenever anyone actually asks for it).

This seems worth investigating. I wonder if it might also fix another bug that I know of involving virtual methods with covariant return types. (You and I actually discussed it at one of the socials a while back, but I have not had time to dig into it further.)

The reproducer for the bug is:

class Foo {};
class Bar : public Foo {};

class Base {
public:
virtual Foo* foo() { return nullptr; }
};

class Derived : public Base {
public:
virtual Bar* foo() { return nullptr; }
};

int main() {
Derived D;
D.foo(); // Evaluate ‘D.foo()’ here, crash LLDB.
}

The issue is that since Bar’s definition is not used its bases are never imported, and so the call to Bar::bases() crashes in CodeGen. If we provided an ExternalASTSource, would that be able to lazily complete the bases?

Yes, such an approach should be able to solve that problem too: when CodeGen (or indeed anything) queries any property of the definition of Foo / Bar (including whether a definition exists), you’ll get a callback and a chance to provide a complete type.

It might be interesting to consider how this is addressed by the ExternalASTSource interface. There, we have separate "import the lexical contents of this AST node (including populating the lexical declarations list with all members, in the right order)", "import the lookup results for this name in this context (and cache them but don't add them to the list of lexical members)" and "import this specific declaration member (but don't add it to the list of lexical members)" queries. One could imagine doing something similar for the AST importer: when you're performing a minimal import but you want to import a method declaration, don't insert it into the list of lexical members of the enclosing record. Instead, defer doing that until a complete type is required (at that point, you'd need to import all the relevant members anyway, including the base classes and virtual functions in the right order).

Hi Richard, maybe my understanding is not correct, but I believe the
situation is somewhat twisted and reversed.
Seems like LLDB already exercises the ExternalASTSource interface. The
purpose of using it is exactly to load the external lexical contents
of an AST node (as you suggested). However, the load is implemented by
the means of the ASTImporter (in minimal mode). Consider the attached
function call trace:
When the user instructs LLDB to evaluate an expression then LLDB
exercises the parser `clang::ParseAST`, which in turn does a lookup
`clang::DeclContext::lookup`. During the lookup,
`lldb_private::ClangASTSource::FindExternalVisibleDeclsByName` is
called (this function overloads
`ExternalASTSource::FindExternalVisibleDeclsByName`).
And finally, through `lldb_private::ClangASTImporter::CopyType` we end
up in `clang::ASTImporter::Import`.

Gabor

#4  0x00007ffff41a72ed in clang::ASTNodeImporter::ImportDeclParts
(this=this@entry=0x7fffffff8be0, D=D@entry=0x632038,
DC=@0x7fffffff8ac8: 0x0,
    LexicalDC=@0x7fffffff8ad0: 0x0, Name=..., ToD=@0x7fffffff8ad8: 0x0, Loc=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/AST/ASTImporter.cpp:1062
#5  0x00007ffff41a8d55 in clang::ASTNodeImporter::VisitRecordDecl
(this=0x7fffffff8be0, D=0x632038)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/AST/ASTImporter.cpp:2126
#6  0x00007ffff419377b in clang::ASTImporter::Import (this=0x70cc90,
FromD=0x632038)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/AST/ASTImporter.cpp:7054
#7  0x00007ffff41939f7 in clang::ASTNodeImporter::VisitRecordType
(this=0x7fffffff8c40, T=<optimized out>)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/AST/ASTImporter.cpp:851
#8  0x00007ffff4196f65 in clang::TypeVisitor<clang::ASTNodeImporter,
clang::QualType>::Visit (this=this@entry=0x7fffffff8c40, T=<optimized
> )

    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/include/clang/AST/TypeNodes.def:92
#9  0x00007ffff4197187 in clang::ASTImporter::Import (this=0x70cc90,
FromT=FromT@entry=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/AST/ASTImporter.cpp:6983
#10 0x00007ffff7351c92 in lldb_private::ClangASTImporter::CopyType
(this=<optimized out>, dst_ast=<optimized out>, src_ast=<optimized
> , type=type@entry=...)

    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:61
#11 0x00007ffff74bdb95 in
lldb_private::ClangASTSource::GuardedCopyType
(this=this@entry=0x611e20, src_type=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:2040
#12 0x00007ffff74e9ffe in
lldb_private::ClangExpressionDeclMap::GetVariableValue
(this=this@entry=0x611e20, var=std::shared_ptr (count 6, weak 1)
0x7fffe80020f0,
    var_location=..., user_type=user_type@entry=0x7fffffff8fc0,
parser_type=parser_type@entry=0x7fffffff8fe0)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:1627
#13 0x00007ffff74ea3a7 in
lldb_private::ClangExpressionDeclMap::AddOneVariable
(this=this@entry=0x611e20, context=...,
    var=std::shared_ptr (count 6, weak 1) 0x7fffe80020f0, valobj=...,
current_id=current_id@entry=2)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:1679
#14 0x00007ffff74ec50b in
lldb_private::ClangExpressionDeclMap::FindExternalVisibleDecls
(this=this@entry=0x611e20, context=..., module_sp=
    std::shared_ptr (empty) 0x0, namespace_decl=...,
current_id=current_id@entry=2)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:1240
#15 0x00007ffff74ef4ce in
lldb_private::ClangExpressionDeclMap::FindExternalVisibleDecls
(this=0x611e20, context=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:843
#16 0x00007ffff74c71cc in
lldb_private::ClangASTSource::FindExternalVisibleDeclsByName
(this=0x611e20, decl_ctx=0x71d8b8, clang_decl_name=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:261
#17 0x00007ffff421d92d in clang::DeclContext::lookup
(this=this@entry=0x71d8b8, Name=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/AST/DeclBase.cpp:1577
#18 0x00007ffff4d4bb42 in LookupDirect (S=..., R=..., DC=DC@entry=0x71d8b8)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Sema/SemaLookup.cpp:843
#19 0x00007ffff4d52f50 in CppNamespaceLookup (S=..., R=...,
NS=NS@entry=0x71d8b8, UDirs=..., Context=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Sema/SemaLookup.cpp:942
#20 0x00007ffff4d53925 in clang::Sema::CppLookupName
(this=this@entry=0x7245b0, R=..., S=0x72cad0)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Sema/SemaLookup.cpp:1322
#21 0x00007ffff4d53c8a in clang::Sema::LookupName (this=0x7245b0,
R=..., S=0x7314f0, AllowBuiltinCreation=<optimized out>)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Sema/SemaLookup.cpp:1827
#22 0x00007ffff4b6b945 in clang::Sema::ClassifyName (this=0x7245b0,
S=0x7314f0, SS=..., Name=@0x7fffffffa3a8: 0x750dc8, NameLoc=...,
NameLoc@entry=...,
    NextToken=..., IsAddressOfOperand=false,
CCC=std::unique_ptr<clang::CorrectionCandidateCallback> containing
0x63c250)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Sema/SemaDecl.cpp:868
#23 0x00007ffff52c6a9f in clang::Parser::TryAnnotateName
(this=this@entry=0x728c60,
IsAddressOfOperand=IsAddressOfOperand@entry=false,
    CCC=std::unique_ptr<clang::CorrectionCandidateCallback> containing
0x0) at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:1531
#24 0x00007ffff52aa56b in
clang::Parser::ParseStatementOrDeclarationAfterAttributes
(this=this@entry=0x728c60, Stmts=...,
    Allowed=Allowed@entry=clang::Parser::ACK_Any,
TrailingElseLoc=<optimized out>, Attrs=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseStmt.cpp:189
#25 0x00007ffff52aa843 in clang::Parser::ParseStatementOrDeclaration
(this=this@entry=0x728c60, Stmts=...,
Allowed=Allowed@entry=clang::Parser::ACK_Any,
    TrailingElseLoc=TrailingElseLoc@entry=0x0) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseStmt.cpp:111
#26 0x00007ffff52ae577 in clang::Parser::ParseCompoundStatementBody
(this=this@entry=0x728c60, isStmtExpr=isStmtExpr@entry=false)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseStmt.cpp:1003
#27 0x00007ffff52b0a49 in clang::Parser::ParseFunctionStatementBody
(this=this@entry=0x728c60, Decl=Decl@entry=0x72dbd0, BodyScope=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseStmt.cpp:1972
#28 0x00007ffff52cc6e0 in clang::Parser::ParseFunctionDefinition
(this=this@entry=0x728c60, D=..., TemplateInfo=...,
    LateParsedAttrs=LateParsedAttrs@entry=0x7fffffffabe0) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:1248
#29 0x00007ffff524aa56 in clang::Parser::ParseDeclGroup
(this=this@entry=0x728c60, DS=...,
Context=Context@entry=clang::DeclaratorContext::FileContext,
    DeclEnd=DeclEnd@entry=0x0, FRI=FRI@entry=0x0) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseDecl.cpp:1968
#30 0x00007ffff52c7f90 in
clang::Parser::ParseDeclOrFunctionDefInternal
(this=this@entry=0x728c60, attrs=..., DS=...,
AS=AS@entry=clang::AS_none)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:1012
#31 0x00007ffff52c8761 in
clang::Parser::ParseDeclarationOrFunctionDefinition (this=0x728c60,
attrs=..., AS=clang::AS_none, DS=0x0)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:1028
#32 0x00007ffff52c87bf in
clang::Parser::ParseDeclarationOrFunctionDefinition (this=<optimized
> , attrs=..., DS=<optimized out>, AS=<optimized out>)

    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:1030
#33 0x00007ffff52cd05d in clang::Parser::ParseExternalDeclaration
(this=this@entry=0x728c60, attrs=..., DS=DS@entry=0x0)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:853
#34 0x00007ffff52ce05c in clang::Parser::ParseTopLevelDecl
(this=this@entry=0x728c60, Result=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/Parser.cpp:609
#35 0x00007ffff522ce1b in clang::ParseAST (S=...,
PrintStats=PrintStats@entry=false,
SkipFunctionBodies=SkipFunctionBodies@entry=false)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseAST.cpp:146
#36 0x00007ffff522d0e0 in clang::ParseAST (PP=..., Consumer=0x535f70,
Ctx=..., PrintStats=<optimized out>, TUKind=clang::TU_Complete,
CompletionConsumer=0x0,
    SkipFunctionBodies=false) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/clang/lib/Parse/ParseAST.cpp:110
#37 0x00007ffff74f0059 in lldb_private::ClangExpressionParser::Parse
(this=this@entry=0x7fffffffcae0, diagnostic_manager=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp:619
#38 0x00007ffff74d23ad in lldb_private::ClangUserExpression::Parse
(this=0x6d23c0, diagnostic_manager=..., exe_ctx=...,
    execution_policy=lldb_private::eExecutionPolicyOnlyWhenNeeded,
keep_result_in_memory=<optimized out>, generate_debug_info=<optimized
> )

    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp:472
---Type <return> to continue, or q <return> to quit---
#39 0x00007ffff72cea9e in lldb_private::UserExpression::Evaluate
(exe_ctx=..., options=..., expr=..., prefix=..., result_valobj_sp=...,
error=..., line_offset=0,
    fixed_expression=0x4bced8, jit_module_sp_ptr=0x0) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Expression/UserExpression.cpp:239
#40 0x00007ffff7401996 in lldb_private::Target::EvaluateExpression
(this=this@entry=0x5b8d10, expr=..., exe_scope=<optimized out>,
result_valobj_sp=...,
    options=..., fixed_expression=0x4bced8) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Target/Target.cpp:2321
#41 0x00007ffff77912dd in
lldb_private::CommandObjectExpression::EvaluateExpression
(this=this@entry=0x4bcb50, expr=expr@entry=0x7fffffffd4c0 "val.v",
    output_stream=output_stream@entry=0x7fffffffd5f0,
error_stream=error_stream@entry=0x7fffffffd648,
result=result@entry=0x7fffffffd5f0)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377
#42 0x00007ffff7792018 in
lldb_private::CommandObjectExpression::DoExecute (this=0x4bcb50,
command=0x7fffffffd4c0 "val.v", result=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:625
#43 0x00007ffff7305baa in lldb_private::CommandObjectRaw::Execute
(this=0x4bcb50, args_string=0x7fffffffd4c0 "val.v", result=...)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Interpreter/CommandObject.cpp:1013
#44 0x00007ffff7302e1b in
lldb_private::CommandInterpreter::HandleCommand
(this=this@entry=0x4a8740, command_line=<optimized out>,
    lazy_add_to_history=lazy_add_to_history@entry=lldb_private::eLazyBoolCalculate,
result=..., override_context=override_context@entry=0x0,
    repeat_on_empty_command=repeat_on_empty_command@entry=true,
no_context_switching=false)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Interpreter/CommandInterpreter.cpp:1683
#45 0x00007ffff73047c8 in
lldb_private::CommandInterpreter::IOHandlerInputComplete
(this=0x4a8740, io_handler=..., line="expr val.v")
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Interpreter/CommandInterpreter.cpp:2771
#46 0x00007ffff723e241 in lldb_private::IOHandlerEditline::Run (this=0x5b4da0)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Core/IOHandler.cpp:573
#47 0x00007ffff720a820 in lldb_private::Debugger::ExecuteIOHandlers
(this=0x4a6f90)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Core/Debugger.cpp:961
#48 0x00007ffff72f731f in
lldb_private::CommandInterpreter::RunCommandInterpreter
(this=0x4a8740, auto_handle_events=auto_handle_events@entry=true,
    spawn_thread=spawn_thread@entry=false, options=...) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/Interpreter/CommandInterpreter.cpp:2971
#49 0x00007ffff7094776 in lldb::SBDebugger::RunCommandInterpreter
(this=this@entry=0x7fffffffda60,
auto_handle_events=auto_handle_events@entry=true,
    spawn_thread=spawn_thread@entry=false) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/source/API/SBDebugger.cpp:892
#50 0x0000000000404a76 in Driver::MainLoop (this=this@entry=0x7fffffffda40)
    at /home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/tools/driver/Driver.cpp:1156
#51 0x0000000000403724 in main (argc=2, argv=0x7fffffffdcb8) at
/home/gerazo/repos/codechecker_dev_env/CTU/llvm/tools/lldb/tools/driver/Driver.cpp:1253

Hi Gábor, Richard,

Hi Richard, maybe my understanding is not correct, but I believe the
situation is somewhat twisted and reversed…

Is this relationship recursive? (Should it be?) I.e. When ClangASTSource uses ASTImporter to minimally import a Decl, should that Decl have another ExternalASTSource attached (possibly the original ClangASTSource) to complete the minimally imported Decl on demand?

– Lang.

Lang,

I've done some more research on this and here is what I've found so far.

LLDB uses the ExternalASTSource interface and it provides its own
implementation for it (lldb_private::ClangASTSource).
ClangASTSource is being used in at least 3 modes (all of these uses
the ASTImporter):
(1) to do a minimal import for a Type/Decl, this is used for lookup
(2) to do a minimal import for a Type/Decl, this is used for computing
the record layout
(3) to complete the Type which has been imported in a minimal mode
previously. The completion is done via ASTImporter::ImportDefinition,
which does a full import of a TagDecl even in minimal mode.

Besides, there is a fourth method which exercises the ASTImporter, but
it does not use the ExternalASTSource interface (4). [[ Actually, (4)
happens before than (3) in program runtime. ]]

So, it is kind of weird to me, that we use a simple minimal import in
(2) for computing the record layout, perhaps we could make a change in
LLDB to call `lldb_private::ClangASTSource::CompleteType` to achieve a
full import in this case? Instead of changing the logic in
clang::ASTImporter? By doing so, I think the logic would be aligned
with Richard's idea.

Gabor

(1)
=== "To" ASTContext A, "From" ASTContext X, MINIMAL import through
ExternalASTSource inteface
clang::ASTImporter::Import (this=0x13b3c50, FromT=...) at
../../git/llvm/tools/clang/lib/AST/ASTImporter.cpp:6983
lldb_private::ClangASTImporter::CopyType (this=0x12a3480,
dst_ast=0x1363420, src_ast=0x11f7980, type=...) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:61
lldb_private::ClangASTSource::GuardedCopyType (this=0x12394b0,
src_type=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:2038
lldb_private::ClangExpressionDeclMap::GetVariableValue
(this=0x12394b0, var=warning: RTTI symbol not found for class
'std::_Sp_counted_ptr<lldb_private::Variable*,
(__gnu_cxx::_Lock_policy)2>'
lldb_private::ClangExpressionDeclMap::AddOneVariable (this=0x12394b0,
context=..., var=warning: RTTI symbol not found for class
'std::_Sp_counted_ptr<lldb_private::Variable*,
(__gnu_cxx::_Lock_policy)2>'
lldb_private::ClangExpressionDeclMap::FindExternalVisibleDecls
(this=0x12394b0, context=..., module_sp=std::shared_ptr (empty) 0x0,
namespace_decl=..., current_id=3) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:1235
lldb_private::ClangExpressionDeclMap::FindExternalVisibleDecls
(this=0x12394b0, context=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:842
lldb_private::ClangASTSource::FindExternalVisibleDeclsByName
(this=0x12394b0, decl_ctx=0x1371298, clang_decl_name=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:261
lldb_private::ClangASTSource::ClangASTSourceProxy::FindExternalVisibleDeclsByName
(this=0x105e230, DC=0x1371298, Name=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.h:244
clang::DeclContext::lookup (this=0x1371298, Name=...) at
../../git/llvm/tools/clang/lib/AST/DeclBase.cpp:1599
LookupDirect (S=..., R=..., DC=0x1371298) at
../../git/llvm/tools/clang/lib/Sema/SemaLookup.cpp:84
CppNamespaceLookup (S=..., R=..., Context=..., NS=0x1d69dd8,
UDirs=...) at ../../git/llvm/tools/clang/lib/Sema/SemaLookup.cpp:942
clang::Sema::CppLookupName (this=0x1d74cd0, R=..., S=0x1d80510) at
../../git/llvm/tools/clang/lib/Sema/SemaLookup.cpp:1322
...
clang::Sema::ActOnUsingDeclaration (this=0x1d74cd0, S=0x1d93820,
AS=clang::AS_none, UsingLoc=..., TypenameLoc=..., SS=..., Name=...,
EllipsisLoc=..., AttrList=...) at
../../git/llvm/tools/clang/lib/Sema/SemaDeclCXX.cpp:9418
clang::Parser::ParseUsingDeclaration (this=0x1d7bd90,
Context=clang::DeclaratorContext::BlockContext, TemplateInfo=...,
UsingLoc=..., DeclEnd=..., AS=clang::AS_none) at
../../git/llvm/tools/clang/lib/Parse/ParseDeclCXX.cpp:710
...
clang::Parser::ParseTopLevelDecl (this=0x1d7bd90, Result=...) at
../../git/llvm/tools/clang/lib/Parse/Parser.cpp:610
clang::ParseAST (S=..., PrintStats=false, SkipFunctionBodies=false) at
../../git/llvm/tools/clang/lib/Parse/ParseAST.cpp:158
clang::ParseAST (PP=..., Consumer=0x1a2dfc0, Ctx=...,
PrintStats=false, TUKind=clang::TU_Complete, CompletionConsumer=0x0,
SkipFunctionBodies=false) at
../../git/llvm/tools/clang/lib/Parse/ParseAST.cpp:111
lldb_private::ClangExpressionParser::Parse (this=0x7fff14cdfe90,
diagnostic_manager=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp:608
lldb_private::ClangUserExpression::Parse (this=0x1d1d530,
diagnostic_manager=..., exe_ctx=...,
execution_policy=lldb_private::eExecutionPolicyOnlyWhenNeeded,
keep_result_in_memory=true, generate_debug_info=false) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp:495
lldb_private::UserExpression::Evaluate (exe_ctx=..., options=...,
expr="tpi", prefix="", result_valobj_sp=..., error=..., line_offset=0,
fixed_expression=0x1a95738, jit_module_sp_ptr=0x0) at
../../git/llvm/tools/lldb/source/Expression/UserExpression.cpp:237
lldb_private::Target::EvaluateExpression (this=0x1b32570, expr="tpi",
exe_scope=0x7fe73ca42d90, result_valobj_sp=..., options=...,
fixed_expression=0x1a95738) at
../../git/llvm/tools/lldb/source/Target/Target.cpp:2308
lldb_private::CommandObjectExpression::EvaluateExpression
(this=0x1a953b0, expr=0x7fff14ce0d58 "tpi",
output_stream=0x7fff14ce16e8, error_stream=0x7fff14ce1740,
result=0x7fff14ce16e8) at
../../git/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377

(2)
=== ASTContext A, "From" ASTContext X, MINIMAL import through
ExternalASTSource inteface
clang::ASTImporter::Import (this=0x13b3c50, FromD=0x13bba18) at
../../git/llvm/tools/clang/lib/AST/ASTImporter.cpp:7040
lldb_private::ClangASTImporter::CopyDecl (this=0x12a3480,
dst_ast=0x1363420, src_ast=0x11f7980, decl=0x13bba18) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:102
lldb_private::ClangASTSource::CopyDecl (this=0x12394b0,
src_decl=0x13bba18) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:1991
lldb_private::ClangASTSource::FindExternalLexicalDecls(clang::DeclContext
const*, llvm::function_ref<bool (clang::Decl::Kind)>,
llvm::SmallVectorImpl<clang::Decl*>&) (this=0x12394b0,
decl_context=0x13b2048, predicate=..., decls=llvm::SmallVector of Size
0, Capacity 64) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:635
lldb_private::ClangASTSource::ClangASTSourceProxy::FindExternalLexicalDecls(clang::DeclContext
const*, llvm::function_ref<bool (clang::Decl::Kind)>,
llvm::SmallVectorImpl<clang::Decl*>&) (this=0x105e230, DC=0x13b2048,
IsKindWeWant=..., Decls=llvm::SmallVector of Size 0, Capacity 64) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.h:251
clang::RecordDecl::LoadFieldsFromExternalStorage (this=0x13b2010) at
../../git/llvm/tools/clang/lib/AST/Decl.cpp:4137
clang::RecordDecl::field_begin (this=0x13b2010) at
../../git/llvm/tools/clang/lib/AST/Decl.cpp:4109
clang::RecordDecl::fields (this=0x13b2010) at
../../git/llvm/tools/clang/include/clang/AST/Decl.h:3751
(anonymous namespace)::EmptySubobjectMap::ComputeEmptySubobjectSizes
(this=0x7fffd5c774d0) at
../../git/llvm/tools/clang/lib/AST/RecordLayoutBuilder.cpp:206
...
clang::CodeGen::CodeGenTypes::ComputeRecordLayout (this=0x1d6e2d8,
D=0x1daab50, Ty=0x1d70550) at
../../git/llvm/tools/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp:725
...
clang::CodeGen::CodeGenModule::EmitTopLevelDecl (this=0x1d6e200,
D=0x1daaa00) at
../../git/llvm/tools/clang/lib/CodeGen/CodeGenModule.cpp:4571
(anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl
(this=0x1d6c620, DG=...) at
../../git/llvm/tools/clang/lib/CodeGen/ModuleBuilder.cpp:160
lldb_private::ASTResultSynthesizer::HandleTopLevelDecl
(this=0x1a2dfc0, D=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp:109
clang::ParseAST (S=..., PrintStats=false, SkipFunctionBodies=false) at
../../git/llvm/tools/clang/lib/Parse/ParseAST.cpp:162
clang::ParseAST (PP=..., Consumer=0x1a2dfc0, Ctx=...,
PrintStats=false, TUKind=clang::TU_Complete, CompletionConsumer=0x0,
SkipFunctionBodies=false) at
../../git/llvm/tools/clang/lib/Parse/ParseAST.cpp:111
lldb_private::ClangExpressionParser::Parse (this=0x7fff14cdfe90,
diagnostic_manager=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp:608
lldb_private::ClangUserExpression::Parse (this=0x1d1d530,
diagnostic_manager=..., exe_ctx=...,
execution_policy=lldb_private::eExecutionPolicyOnlyWhenNeeded,
keep_result_in_memory=true, generate_debug_info=false) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp:495
lldb_private::UserExpression::Evaluate (exe_ctx=..., options=...,
expr="tpi", prefix="", result_valobj_sp=..., error=..., line_offset=0,
fixed_expression=0x1a95738, jit_module_sp_ptr=0x0) at
../../git/llvm/tools/lldb/source/Expression/UserExpression.cpp:237
lldb_private::Target::EvaluateExpression (this=0x1b32570, expr="tpi",
exe_scope=0x7fe73ca42d90, result_valobj_sp=..., options=...,
fixed_expression=0x1a95738) at
../../git/llvm/tools/lldb/source/Target/Target.cpp:2308
lldb_private::CommandObjectExpression::EvaluateExpression
(this=0x1a953b0, expr=0x7fff14ce0d58 "tpi",
output_stream=0x7fff14ce16e8, error_stream=0x7fff14ce1740,
result=0x7fff14ce16e8) at
../../git/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377

(3)
=== ASTContext B, "From" ASTContext Z, ASTImporter is in MINIMAL mode,
but ImportDefinition forces a full import
clang::ASTImporter::ImportDefinition (this=0x1d75200, From=0x1c01048)
at ../../git/llvm/tools/clang/lib/AST/ASTImporter.cpp:7519
lldb_private::ClangASTImporter::Minion::ImportDefinitionTo
(this=0x1d75200, to=0x1d1b8d8, from=0x1c01048) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:889
lldb_private::ClangASTImporter::CompleteTagDecl (this=0x1c96360,
decl=0x1d1b8d8) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:560
lldb_private::ClangASTSource::CompleteType (this=0x1a66560,
tag_decl=0x1d1b8d8) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:299
lldb_private::ClangASTSource::ClangASTSourceProxy::CompleteType
(this=0x1a24d60, Tag=0x1d1b8d8) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.h:255
GetCompleteQualType (ast=0x1cde470, qual_type=...,
allow_completion=true) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:2515
lldb_private::ClangASTContext::GetNumChildren (this=0x1c456f0,
type=0x1d1b980, omit_empty_base_classes=true) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:5341
lldb_private::CompilerType::GetNumChildren (this=0x7fff14cdfe18,
omit_empty_base_classes=true) at
../../git/llvm/tools/lldb/source/Symbol/CompilerType.cpp:541
lldb_private::ClangASTContext::GetNumChildren (this=0x1c456f0,
type=0x1d1ba10, omit_empty_base_classes=true) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:5443
lldb_private::CompilerType::GetNumChildren (this=0x7fff14ce0018,
omit_empty_base_classes=true) at
../../git/llvm/tools/lldb/source/Symbol/CompilerType.cpp:541
lldb_private::ClangASTContext::GetNumChildren (this=0x1c456f0,
type=0x1d1baa0, omit_empty_base_classes=true) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:5472
lldb_private::CompilerType::GetNumChildren (this=0x7fff14ce01d0,
omit_empty_base_classes=true) at
../../git/llvm/tools/lldb/source/Symbol/CompilerType.cpp:541
lldb_private::ValueObjectConstResult::CalculateNumChildren
(this=0x1d6c620, max=4294967295) at
../../git/llvm/tools/lldb/source/Core/ValueObjectConstResult.cpp:211
lldb_private::ValueObject::GetNumChildren (this=0x1d6c620,
max=4294967295) at
../../git/llvm/tools/lldb/source/Core/ValueObject.cpp:601
lldb_private::FormatManager::ShouldPrintAsOneLiner
(this=0x7fe7676031d8 <GetFormatManager()::g_format_manager>,
valobj=...) at ../../git/llvm/tools/lldb/source/DataFormatters/FormatManager.cpp:494
lldb_private::DataVisualization::ShouldPrintAsOneLiner (valobj=...) at
../../git/llvm/tools/lldb/source/DataFormatters/DataVisualization.cpp:33
lldb_private::ValueObjectPrinter::PrintChildrenIfNeeded
(this=0x7fff14ce0560, value_printed=true, summary_printed=false) at
../../git/llvm/tools/lldb/source/DataFormatters/ValueObjectPrinter.cpp:771
lldb_private::ValueObjectPrinter::PrintValueObject
...
lldb_private::ValueObject::Dump (this=0x1d6c620, s=..., options=...)
at ../../git/llvm/tools/lldb/source/Core/ValueObject.cpp:2742
lldb_private::CommandObjectExpression::EvaluateExpression

(4)
==== ASTContext B, "From" ASTContext Y, MINIMAL import, skips
ExternalASTSource interface
clang::ASTImporter::Import (this=0x1d74cd0, FromT=...) at
../../git/llvm/tools/clang/lib/AST/ASTImporter.cpp:6983
lldb_private::ClangASTImporter::CopyType (this=0x1c96360,
dst_ast=0x1cde470, src_ast=0x1d5bf60, type=...) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:61
lldb_private::ClangASTImporter::CopyType (this=0x1c96360,
dst_ast=0x1cde470, src_ast=0x1d5bf60, type=0x1daad10) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:70
lldb_private::ClangASTImporter::DeportType (this=0x1c96360,
dst_ctx=0x1cde470, src_ctx=0x1d5bf60, type=0x1daad10) at
../../git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:268
lldb_private::ClangExpressionDeclMap::DeportType (this=0x1c98e00,
target=..., source=..., parser_type=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:288
lldb_private::ClangExpressionDeclMap::AddPersistentVariable
(this=0x1c98e00, decl=0x1daaff8, name=..., parser_type=...,
is_result=true, is_lvalue=true) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:332
IRForTarget::CreateResultVariable (this=0x7fff14cdf8c0,
llvm_function=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp:407
IRForTarget::runOnModule (this=0x7fff14cdf8c0, llvm_module=...) at
../../git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp:2102
lldb_private::ClangExpressionParser::PrepareForExecution
...
lldb_private::CommandObjectExpression::EvaluateExpression
(this=0x1a953b0, expr=0x7fff14ce0d58 "tpi",
output_stream=0x7fff14ce16e8, error_stream=0x7fff14ce1740,
result=0x7fff14ce16e8) at
../../git/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377

Just sending again the trace, because gmail broke the lines pretty badly.

(1)
=== “To” ASTContext A, “From” ASTContext X, MINIMAL import through ExternalASTSource inteface
clang::ASTImporter::Import (this=0x13b3c50, FromT=…) at …/…/git/llvm/tools/clang/lib/AST/ASTImporter.cpp:6983
lldb_private::ClangASTImporter::CopyType (this=0x12a3480, dst_ast=0x1363420, src_ast=0x11f7980, type=…) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:61
lldb_private::ClangASTSource::GuardedCopyType (this=0x12394b0, src_type=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:2038
lldb_private::ClangExpressionDeclMap::GetVariableValue (this=0x12394b0, var=warning: RTTI symbol not found for class ‘std::_Sp_counted_ptr<lldb_private::Variable*, (__gnu_cxx::_Lock_policy)2>’
lldb_private::ClangExpressionDeclMap::AddOneVariable (this=0x12394b0, context=…, var=warning: RTTI symbol not found for class ‘std::_Sp_counted_ptr<lldb_private::Variable*, (__gnu_cxx::_Lock_policy)2>’
lldb_private::ClangExpressionDeclMap::FindExternalVisibleDecls (this=0x12394b0, context=…, module_sp=std::shared_ptr (empty) 0x0, namespace_decl=…, current_id=3) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:1235
lldb_private::ClangExpressionDeclMap::FindExternalVisibleDecls (this=0x12394b0, context=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:842
lldb_private::ClangASTSource::FindExternalVisibleDeclsByName (this=0x12394b0, decl_ctx=0x1371298, clang_decl_name=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:261
lldb_private::ClangASTSource::ClangASTSourceProxy::FindExternalVisibleDeclsByName (this=0x105e230, DC=0x1371298, Name=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.h:244
clang::DeclContext::lookup (this=0x1371298, Name=…) at …/…/git/llvm/tools/clang/lib/AST/DeclBase.cpp:1599
LookupDirect (S=…, R=…, DC=0x1371298) at …/…/git/llvm/tools/clang/lib/Sema/SemaLookup.cpp:84
CppNamespaceLookup (S=…, R=…, Context=…, NS=0x1d69dd8, UDirs=…) at …/…/git/llvm/tools/clang/lib/Sema/SemaLookup.cpp:942
clang::Sema::CppLookupName (this=0x1d74cd0, R=…, S=0x1d80510) at …/…/git/llvm/tools/clang/lib/Sema/SemaLookup.cpp:1322

clang::Sema::ActOnUsingDeclaration (this=0x1d74cd0, S=0x1d93820, AS=clang::AS_none, UsingLoc=…, TypenameLoc=…, SS=…, Name=…, EllipsisLoc=…, AttrList=…) at …/…/git/llvm/tools/clang/lib/Sema/SemaDeclCXX.cpp:9418
clang::Parser::ParseUsingDeclaration (this=0x1d7bd90, Context=clang::DeclaratorContext::BlockContext, TemplateInfo=…, UsingLoc=…, DeclEnd=…, AS=clang::AS_none) at …/…/git/llvm/tools/clang/lib/Parse/ParseDeclCXX.cpp:710

clang::Parser::ParseTopLevelDecl (this=0x1d7bd90, Result=…) at …/…/git/llvm/tools/clang/lib/Parse/Parser.cpp:610
clang::ParseAST (S=…, PrintStats=false, SkipFunctionBodies=false) at …/…/git/llvm/tools/clang/lib/Parse/ParseAST.cpp:158
clang::ParseAST (PP=…, Consumer=0x1a2dfc0, Ctx=…, PrintStats=false, TUKind=clang::TU_Complete, CompletionConsumer=0x0, SkipFunctionBodies=false) at …/…/git/llvm/tools/clang/lib/Parse/ParseAST.cpp:111
lldb_private::ClangExpressionParser::Parse (this=0x7fff14cdfe90, diagnostic_manager=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp:608
lldb_private::ClangUserExpression::Parse (this=0x1d1d530, diagnostic_manager=…, exe_ctx=…, execution_policy=lldb_private::eExecutionPolicyOnlyWhenNeeded, keep_result_in_memory=true, generate_debug_info=false) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp:495
lldb_private::UserExpression::Evaluate (exe_ctx=…, options=…, expr=“tpi”, prefix="", result_valobj_sp=…, error=…, line_offset=0, fixed_expression=0x1a95738, jit_module_sp_ptr=0x0) at …/…/git/llvm/tools/lldb/source/Expression/UserExpression.cpp:237
lldb_private::Target::EvaluateExpression (this=0x1b32570, expr=“tpi”, exe_scope=0x7fe73ca42d90, result_valobj_sp=…, options=…, fixed_expression=0x1a95738) at …/…/git/llvm/tools/lldb/source/Target/Target.cpp:2308
lldb_private::CommandObjectExpression::EvaluateExpression (this=0x1a953b0, expr=0x7fff14ce0d58 “tpi”, output_stream=0x7fff14ce16e8, error_stream=0x7fff14ce1740, result=0x7fff14ce16e8) at …/…/git/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377

(2)
=== ASTContext A, “From” ASTContext X, MINIMAL import through ExternalASTSource inteface
clang::ASTImporter::Import (this=0x13b3c50, FromD=0x13bba18) at …/…/git/llvm/tools/clang/lib/AST/ASTImporter.cpp:7040
lldb_private::ClangASTImporter::CopyDecl (this=0x12a3480, dst_ast=0x1363420, src_ast=0x11f7980, decl=0x13bba18) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:102
lldb_private::ClangASTSource::CopyDecl (this=0x12394b0, src_decl=0x13bba18) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:1991
lldb_private::ClangASTSource::FindExternalLexicalDecls(clang::DeclContext const*, llvm::function_ref<bool (clang::Decl::Kind)>, llvm::SmallVectorImplclang::Decl*&) (this=0x12394b0, decl_context=0x13b2048, predicate=…, decls=llvm::SmallVector of Size 0, Capacity 64) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:635
lldb_private::ClangASTSource::ClangASTSourceProxy::FindExternalLexicalDecls(clang::DeclContext const*, llvm::function_ref<bool (clang::Decl::Kind)>, llvm::SmallVectorImplclang::Decl*&) (this=0x105e230, DC=0x13b2048, IsKindWeWant=…, Decls=llvm::SmallVector of Size 0, Capacity 64) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.h:251
clang::RecordDecl::LoadFieldsFromExternalStorage (this=0x13b2010) at …/…/git/llvm/tools/clang/lib/AST/Decl.cpp:4137
clang::RecordDecl::field_begin (this=0x13b2010) at …/…/git/llvm/tools/clang/lib/AST/Decl.cpp:4109
clang::RecordDecl::fields (this=0x13b2010) at …/…/git/llvm/tools/clang/include/clang/AST/Decl.h:3751
(anonymous namespace)::EmptySubobjectMap::ComputeEmptySubobjectSizes (this=0x7fffd5c774d0) at …/…/git/llvm/tools/clang/lib/AST/RecordLayoutBuilder.cpp:206

clang::CodeGen::CodeGenTypes::ComputeRecordLayout (this=0x1d6e2d8, D=0x1daab50, Ty=0x1d70550) at …/…/git/llvm/tools/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp:725

clang::CodeGen::CodeGenModule::EmitTopLevelDecl (this=0x1d6e200, D=0x1daaa00) at …/…/git/llvm/tools/clang/lib/CodeGen/CodeGenModule.cpp:4571
(anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl (this=0x1d6c620, DG=…) at …/…/git/llvm/tools/clang/lib/CodeGen/ModuleBuilder.cpp:160
lldb_private::ASTResultSynthesizer::HandleTopLevelDecl (this=0x1a2dfc0, D=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp:109
clang::ParseAST (S=…, PrintStats=false, SkipFunctionBodies=false) at …/…/git/llvm/tools/clang/lib/Parse/ParseAST.cpp:162
clang::ParseAST (PP=…, Consumer=0x1a2dfc0, Ctx=…, PrintStats=false, TUKind=clang::TU_Complete, CompletionConsumer=0x0, SkipFunctionBodies=false) at …/…/git/llvm/tools/clang/lib/Parse/ParseAST.cpp:111
lldb_private::ClangExpressionParser::Parse (this=0x7fff14cdfe90, diagnostic_manager=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp:608
lldb_private::ClangUserExpression::Parse (this=0x1d1d530, diagnostic_manager=…, exe_ctx=…, execution_policy=lldb_private::eExecutionPolicyOnlyWhenNeeded, keep_result_in_memory=true, generate_debug_info=false) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp:495
lldb_private::UserExpression::Evaluate (exe_ctx=…, options=…, expr=“tpi”, prefix="", result_valobj_sp=…, error=…, line_offset=0, fixed_expression=0x1a95738, jit_module_sp_ptr=0x0) at …/…/git/llvm/tools/lldb/source/Expression/UserExpression.cpp:237
lldb_private::Target::EvaluateExpression (this=0x1b32570, expr=“tpi”, exe_scope=0x7fe73ca42d90, result_valobj_sp=…, options=…, fixed_expression=0x1a95738) at …/…/git/llvm/tools/lldb/source/Target/Target.cpp:2308
lldb_private::CommandObjectExpression::EvaluateExpression (this=0x1a953b0, expr=0x7fff14ce0d58 “tpi”, output_stream=0x7fff14ce16e8, error_stream=0x7fff14ce1740, result=0x7fff14ce16e8) at …/…/git/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377

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=== ASTContext B, “From” ASTContext Z, ASTImporter is in MINIMAL mode, but ImportDefinition forces a full import
clang::ASTImporter::ImportDefinition (this=0x1d75200, From=0x1c01048) at …/…/git/llvm/tools/clang/lib/AST/ASTImporter.cpp:7519
lldb_private::ClangASTImporter::Minion::ImportDefinitionTo (this=0x1d75200, to=0x1d1b8d8, from=0x1c01048) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:889
lldb_private::ClangASTImporter::CompleteTagDecl (this=0x1c96360, decl=0x1d1b8d8) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:560
lldb_private::ClangASTSource::CompleteType (this=0x1a66560, tag_decl=0x1d1b8d8) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp:299
lldb_private::ClangASTSource::ClangASTSourceProxy::CompleteType (this=0x1a24d60, Tag=0x1d1b8d8) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.h:255
GetCompleteQualType (ast=0x1cde470, qual_type=…, allow_completion=true) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:2515
lldb_private::ClangASTContext::GetNumChildren (this=0x1c456f0, type=0x1d1b980, omit_empty_base_classes=true) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:5341
lldb_private::CompilerType::GetNumChildren (this=0x7fff14cdfe18, omit_empty_base_classes=true) at …/…/git/llvm/tools/lldb/source/Symbol/CompilerType.cpp:541
lldb_private::ClangASTContext::GetNumChildren (this=0x1c456f0, type=0x1d1ba10, omit_empty_base_classes=true) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:5443
lldb_private::CompilerType::GetNumChildren (this=0x7fff14ce0018, omit_empty_base_classes=true) at …/…/git/llvm/tools/lldb/source/Symbol/CompilerType.cpp:541
lldb_private::ClangASTContext::GetNumChildren (this=0x1c456f0, type=0x1d1baa0, omit_empty_base_classes=true) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTContext.cpp:5472
lldb_private::CompilerType::GetNumChildren (this=0x7fff14ce01d0, omit_empty_base_classes=true) at …/…/git/llvm/tools/lldb/source/Symbol/CompilerType.cpp:541
lldb_private::ValueObjectConstResult::CalculateNumChildren (this=0x1d6c620, max=4294967295) at …/…/git/llvm/tools/lldb/source/Core/ValueObjectConstResult.cpp:211
lldb_private::ValueObject::GetNumChildren (this=0x1d6c620, max=4294967295) at …/…/git/llvm/tools/lldb/source/Core/ValueObject.cpp:601
lldb_private::FormatManager::ShouldPrintAsOneLiner (this=0x7fe7676031d8 <GetFormatManager()::g_format_manager>, valobj=…) at …/…/git/llvm/tools/lldb/source/DataFormatters/FormatManager.cpp:494
lldb_private::DataVisualization::ShouldPrintAsOneLiner (valobj=…) at …/…/git/llvm/tools/lldb/source/DataFormatters/DataVisualization.cpp:33
lldb_private::ValueObjectPrinter::PrintChildrenIfNeeded (this=0x7fff14ce0560, value_printed=true, summary_printed=false) at …/…/git/llvm/tools/lldb/source/DataFormatters/ValueObjectPrinter.cpp:771
lldb_private::ValueObjectPrinter::PrintValueObject

lldb_private::ValueObject::Dump (this=0x1d6c620, s=…, options=…) at …/…/git/llvm/tools/lldb/source/Core/ValueObject.cpp:2742
lldb_private::CommandObjectExpression::EvaluateExpression

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==== ASTContext B, “From” ASTContext Y, MINIMAL import, skips ExternalASTSource interface
clang::ASTImporter::Import (this=0x1d74cd0, FromT=…) at …/…/git/llvm/tools/clang/lib/AST/ASTImporter.cpp:6983
lldb_private::ClangASTImporter::CopyType (this=0x1c96360, dst_ast=0x1cde470, src_ast=0x1d5bf60, type=…) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:61
lldb_private::ClangASTImporter::CopyType (this=0x1c96360, dst_ast=0x1cde470, src_ast=0x1d5bf60, type=0x1daad10) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:70
lldb_private::ClangASTImporter::DeportType (this=0x1c96360, dst_ctx=0x1cde470, src_ctx=0x1d5bf60, type=0x1daad10) at …/…/git/llvm/tools/lldb/source/Symbol/ClangASTImporter.cpp:268
lldb_private::ClangExpressionDeclMap::DeportType (this=0x1c98e00, target=…, source=…, parser_type=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:288
lldb_private::ClangExpressionDeclMap::AddPersistentVariable (this=0x1c98e00, decl=0x1daaff8, name=…, parser_type=…, is_result=true, is_lvalue=true) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp:332
IRForTarget::CreateResultVariable (this=0x7fff14cdf8c0, llvm_function=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp:407
IRForTarget::runOnModule (this=0x7fff14cdf8c0, llvm_module=…) at …/…/git/llvm/tools/lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp:2102
lldb_private::ClangExpressionParser::PrepareForExecution

lldb_private::CommandObjectExpression::EvaluateExpression (this=0x1a953b0, expr=0x7fff14ce0d58 “tpi”, output_stream=0x7fff14ce16e8, error_stream=0x7fff14ce1740, result=0x7fff14ce16e8) at …/…/git/llvm/tools/lldb/source/Commands/CommandObjectExpression.cpp:377

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