[Lldb-commits] [lldb] [lldb] Fix dynamic type resolution for types parsed from declarations (PR #137974)
Pavel Labath via lldb-commits
lldb-commits at lists.llvm.org
Wed Apr 30 07:53:21 PDT 2025
https://github.com/labath created https://github.com/llvm/llvm-project/pull/137974
This fixes a regression caused by us starting to parse types from declarations. The code in TypeSystemClang was assuming that the value held in ClangASTMetadata was authoritative, but this isn't (and cannot) be the case when the type is parsed from a forward-declaration.
For the fix, I add a new "don't know" state to ClangASTMetadata, and make sure DWARFASTParserClang sets it only when it encounters a forward declaration. In this case, the type system will fall back to completing the type.
This does mean that we will be completing more types than before, but I'm hoping this will offset by the fact that we don't search for definition DIEs eagerly. In particular, I don't make a difference in -fstandalone-debug scenarios, since types will nearly always be present as definitions.
To avoid this cost, we'd need to create some sort of a back channel to query the DWARFASTParser about the dynamicness of the type without actually completing it. I'd like to avoid that if it is not necessary.
>From 78d25e30f56af996278730cd4b4db99401552d6f Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel at labath.sk>
Date: Wed, 30 Apr 2025 16:23:39 +0200
Subject: [PATCH] [lldb] Fix dynamic type resolution for types parsed from
declarations
This fixes a regression caused by us starting to parse types from
declarations. The code in TypeSystemClang was assuming that the value
held in ClangASTMetadata was authoritative, but this isn't (and cannot)
be the case when the type is parsed from a forward-declaration.
For the fix, I add a new "don't know" state to ClangASTMetadata, and
make sure DWARFASTParserClang sets it only when it encounters a forward
declaration. In this case, the type system will fall back to
completing the type.
This does mean that we will be completing more types than before, but
I'm hoping this will offset by the fact that we don't search for
definition DIEs eagerly. In particular, I don't make a difference in
-fstandalone-debug scenarios, since types will nearly always be present
as definitions.
To avoid this cost, we'd need to create some sort of a back channel to
query the DWARFASTParser about the dynamicness of the type without
actually completing it. I'd like to avoid that if it is not necessary.
---
.../Clang/ClangASTMetadata.cpp | 16 ++++++++++++++++
.../ExpressionParser/Clang/ClangASTMetadata.h | 15 +++++++++------
.../SymbolFile/DWARF/DWARFASTParserClang.cpp | 3 ++-
.../TypeSystem/Clang/TypeSystemClang.cpp | 18 +++++++++++-------
lldb/test/API/lang/cpp/dynamic-value/Makefile | 2 +-
.../lang/cpp/dynamic-value/TestDynamicValue.py | 12 ++++++++++++
lldb/test/API/lang/cpp/dynamic-value/a.h | 2 ++
.../API/lang/cpp/dynamic-value/forward-a.cpp | 3 +++
.../lang/cpp/dynamic-value/pass-to-base.cpp | 2 ++
9 files changed, 58 insertions(+), 15 deletions(-)
create mode 100644 lldb/test/API/lang/cpp/dynamic-value/forward-a.cpp
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.cpp
index 42933c78b0277..2c5dacb60a9b8 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.cpp
@@ -11,6 +11,22 @@
using namespace lldb_private;
+std::optional<bool> ClangASTMetadata::GetIsDynamicCXXType() const {
+ switch (m_is_dynamic_cxx) {
+ case 0:
+ return std::nullopt;
+ case 1:
+ return false;
+ case 2:
+ return true;
+ }
+ llvm_unreachable("Invalid m_is_dynamic_cxx value");
+}
+
+void ClangASTMetadata::SetIsDynamicCXXType(std::optional<bool> b) {
+ m_is_dynamic_cxx = b ? *b + 1 : 0;
+}
+
void ClangASTMetadata::Dump(Stream *s) {
lldb::user_id_t uid = GetUserID();
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.h b/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.h
index d3bcde2ced799..ecaa2e0ddf97c 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.h
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangASTMetadata.h
@@ -12,6 +12,7 @@
#include "lldb/Core/dwarf.h"
#include "lldb/lldb-defines.h"
#include "lldb/lldb-enumerations.h"
+#include "lldb/lldb-private-enumerations.h"
namespace lldb_private {
@@ -19,12 +20,14 @@ class ClangASTMetadata {
public:
ClangASTMetadata()
: m_user_id(0), m_union_is_user_id(false), m_union_is_isa_ptr(false),
- m_has_object_ptr(false), m_is_self(false), m_is_dynamic_cxx(true),
- m_is_forcefully_completed(false) {}
+ m_has_object_ptr(false), m_is_self(false),
+ m_is_forcefully_completed(false) {
+ SetIsDynamicCXXType(std::nullopt);
+ }
- bool GetIsDynamicCXXType() const { return m_is_dynamic_cxx; }
+ std::optional<bool> GetIsDynamicCXXType() const;
- void SetIsDynamicCXXType(bool b) { m_is_dynamic_cxx = b; }
+ void SetIsDynamicCXXType(std::optional<bool> b);
void SetUserID(lldb::user_id_t user_id) {
m_user_id = user_id;
@@ -101,8 +104,8 @@ class ClangASTMetadata {
uint64_t m_isa_ptr;
};
- bool m_union_is_user_id : 1, m_union_is_isa_ptr : 1, m_has_object_ptr : 1,
- m_is_self : 1, m_is_dynamic_cxx : 1, m_is_forcefully_completed : 1;
+ unsigned m_union_is_user_id : 1, m_union_is_isa_ptr : 1, m_has_object_ptr : 1,
+ m_is_self : 1, m_is_dynamic_cxx : 2, m_is_forcefully_completed : 1;
};
} // namespace lldb_private
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
index f22fcbab557a0..a3e809f44ed23 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -1837,7 +1837,8 @@ DWARFASTParserClang::ParseStructureLikeDIE(const SymbolContext &sc,
ClangASTMetadata metadata;
metadata.SetUserID(die.GetID());
- metadata.SetIsDynamicCXXType(dwarf->ClassOrStructIsVirtual(die));
+ if (!attrs.is_forward_declaration)
+ metadata.SetIsDynamicCXXType(dwarf->ClassOrStructIsVirtual(die));
TypeSystemClang::TemplateParameterInfos template_param_infos;
if (ParseTemplateParameterInfos(die, template_param_infos)) {
diff --git a/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp b/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
index cb0ecd6ebd406..1a2b3d4133e51 100644
--- a/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
+++ b/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
@@ -3657,13 +3657,17 @@ bool TypeSystemClang::IsPossibleDynamicType(lldb::opaque_compiler_type_t type,
bool success;
if (cxx_record_decl->isCompleteDefinition())
success = cxx_record_decl->isDynamicClass();
- else if (std::optional<ClangASTMetadata> metadata =
- GetMetadata(cxx_record_decl))
- success = metadata->GetIsDynamicCXXType();
- else if (GetType(pointee_qual_type).GetCompleteType())
- success = cxx_record_decl->isDynamicClass();
- else
- success = false;
+ else {
+ std::optional<ClangASTMetadata> metadata = GetMetadata(cxx_record_decl);
+ std::optional<bool> is_dynamic =
+ metadata ? metadata->GetIsDynamicCXXType() : std::nullopt;
+ if (is_dynamic)
+ success = *is_dynamic;
+ else if (GetType(pointee_qual_type).GetCompleteType())
+ success = cxx_record_decl->isDynamicClass();
+ else
+ success = false;
+ }
if (success)
set_dynamic_pointee_type(pointee_qual_type);
diff --git a/lldb/test/API/lang/cpp/dynamic-value/Makefile b/lldb/test/API/lang/cpp/dynamic-value/Makefile
index ce91dc63f473f..24346ccfae510 100644
--- a/lldb/test/API/lang/cpp/dynamic-value/Makefile
+++ b/lldb/test/API/lang/cpp/dynamic-value/Makefile
@@ -1,3 +1,3 @@
-CXX_SOURCES := pass-to-base.cpp anonymous-b.cpp
+CXX_SOURCES := pass-to-base.cpp anonymous-b.cpp forward-a.cpp
include Makefile.rules
diff --git a/lldb/test/API/lang/cpp/dynamic-value/TestDynamicValue.py b/lldb/test/API/lang/cpp/dynamic-value/TestDynamicValue.py
index 32ef009279713..c0e7c52e5396e 100644
--- a/lldb/test/API/lang/cpp/dynamic-value/TestDynamicValue.py
+++ b/lldb/test/API/lang/cpp/dynamic-value/TestDynamicValue.py
@@ -266,3 +266,15 @@ def examine_value_object_of_this_ptr(
contained_b_static_addr = int(contained_b_static.GetValue(), 16)
self.assertLess(contained_b_addr, contained_b_static_addr)
+
+ @no_debug_info_test
+ def test_from_forward_decl(self):
+ """Test fetching C++ dynamic values forward-declared types. It's
+ imperative that this is a separate test so that we don't end up parsing
+ a definition of A from somewhere else."""
+ self.build()
+ lldbutil.run_to_name_breakpoint(self, "take_A")
+ self.expect(
+ "frame var -d run-target --ptr-depth=1 --show-types a",
+ substrs = ["(B *) a", "m_b_value = 10"],
+ )
diff --git a/lldb/test/API/lang/cpp/dynamic-value/a.h b/lldb/test/API/lang/cpp/dynamic-value/a.h
index 708cbb79fee5c..c8895ab095d82 100644
--- a/lldb/test/API/lang/cpp/dynamic-value/a.h
+++ b/lldb/test/API/lang/cpp/dynamic-value/a.h
@@ -22,4 +22,6 @@ class A {
A *make_anonymous_B();
+A *take_A(A *a);
+
#endif
diff --git a/lldb/test/API/lang/cpp/dynamic-value/forward-a.cpp b/lldb/test/API/lang/cpp/dynamic-value/forward-a.cpp
new file mode 100644
index 0000000000000..8a212d928d5c5
--- /dev/null
+++ b/lldb/test/API/lang/cpp/dynamic-value/forward-a.cpp
@@ -0,0 +1,3 @@
+class A;
+
+A *take_A(A *a) { return a; }
diff --git a/lldb/test/API/lang/cpp/dynamic-value/pass-to-base.cpp b/lldb/test/API/lang/cpp/dynamic-value/pass-to-base.cpp
index be763390cc6f9..9b601084cdc57 100644
--- a/lldb/test/API/lang/cpp/dynamic-value/pass-to-base.cpp
+++ b/lldb/test/API/lang/cpp/dynamic-value/pass-to-base.cpp
@@ -45,5 +45,7 @@ main (int argc, char **argv)
myB.doSomething(*make_anonymous_B());
+ take_A(&myB);
+
return 0;
}
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