https://github.com/chbessonova created
https://github.com/llvm/llvm-project/pull/206740
Lambdas appearing in default member initializers of members of local classes
were previously mangled as if they belonged only to the class scope, ignoring
the enclosing function-local context.
This caused different (but same-named) local classes to produce identical
closure type mangling and corresponding RTTI/IR collisions.
Consider the following example:
```
void foo() {
{
struct T {
std::function<void()> a = [](){ std::cout << "a"; };
} t;
t.a();
}
{
struct T {
std::function<void()> a = [](){ std::cout << "b"; };
} t;
t.a();
}
}
```
The expected output is `ab` (and GCC-compiled code behaves accordingly), while
clang previously printed `aa` because the second `T::a` definition never
reached IR generation due to the missing `<local-name>` encoding and
discriminator required to distinguish the two local `T` definitions.
>From 2004b67caee32114459d79831a3a1e151d54e2f4 Mon Sep 17 00:00:00 2001
From: Kristina Bessonova <[email protected]>
Date: Mon, 29 Jun 2026 21:56:40 +0200
Subject: [PATCH] [clang][ItaniumMangle] Fix mangling of lambdas in default
member initializers of local classes
Lambdas appearing in default member initializers of members of local
classes were previously mangled as if they belonged only to the class
scope, ignoring the enclosing function-local context.
This caused different (but same-named) local classes to produce identical
closure type manglings and corresponding RTTI/IR collisions.
Consider the following example:
```
void foo() {
{
struct T {
std::function<void()> a = [](){ std::cout << "a"; };
} t;
t.a();
}
{
struct T {
std::function<void()> a = [](){ std::cout << "b"; };
} t;
t.a();
}
}
```
The expected output is `ab` (and GCC-compiled code behaves accordingly),
while clang previously printed `aa` because the second `T::a` definition
never reached IR generation due to the missing `<local-name>` encoding and
discriminator required to distinguish the two local `T` definitions.
---
clang/lib/AST/ItaniumMangle.cpp | 20 +++---
.../CodeGenCXX/dtor-local-lambda-mangle.cpp | 6 +-
.../CodeGenCXX/mangle-lambdas-gh88906.cpp | 12 ++--
.../mangle-lambdas-in-dmi-local-class.cpp | 65 +++++++++++++++++++
4 files changed, 86 insertions(+), 17 deletions(-)
create mode 100644 clang/test/CodeGenCXX/mangle-lambdas-in-dmi-local-class.cpp
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index e5cdd6f31c507..e014b45a5da93 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -530,7 +530,8 @@ class CXXNameMangler {
ArrayRef<TemplateArgument> Args);
void mangleNestedNameWithClosurePrefix(GlobalDecl GD,
const NamedDecl *PrefixND,
- ArrayRef<StringRef>
AdditionalAbiTags);
+ ArrayRef<StringRef> AdditionalAbiTags,
+ bool NoFunction = false);
void manglePrefix(NestedNameSpecifier Qualifier);
void manglePrefix(const DeclContext *DC, bool NoFunction=false);
void manglePrefix(QualType type);
@@ -1067,10 +1068,8 @@ void CXXNameMangler::mangleNameWithAbiTags(
// ::= <local-name>
//
const DeclContext *DC = Context.getEffectiveDeclContext(ND);
- bool IsLambda = isLambda(ND);
- if (GetLocalClassDecl(ND) &&
- (!IsLambda || isCompatibleWith(LangOptions::ClangABI::Ver18))) {
+ if (GetLocalClassDecl(ND)) {
mangleLocalName(GD, AdditionalAbiTags);
return;
}
@@ -1845,7 +1844,7 @@ void CXXNameMangler::mangleNestedName(const TemplateDecl
*TD,
void CXXNameMangler::mangleNestedNameWithClosurePrefix(
GlobalDecl GD, const NamedDecl *PrefixND,
- ArrayRef<StringRef> AdditionalAbiTags) {
+ ArrayRef<StringRef> AdditionalAbiTags, bool NoFunction) {
// A <closure-prefix> represents a variable or field, not a regular
// DeclContext, so needs special handling. In this case we're mangling a
// limited form of <nested-name>:
@@ -1854,7 +1853,7 @@ void CXXNameMangler::mangleNestedNameWithClosurePrefix(
Out << 'N';
- mangleClosurePrefix(PrefixND);
+ mangleClosurePrefix(PrefixND, NoFunction);
mangleUnqualifiedName(GD, nullptr, AdditionalAbiTags);
Out << 'E';
@@ -1945,8 +1944,13 @@ void CXXNameMangler::mangleLocalName(GlobalDecl GD,
mangleUnqualifiedBlock(BD);
} else {
const NamedDecl *ND = cast<NamedDecl>(D);
- mangleNestedName(GD, Context.getEffectiveDeclContext(ND),
- AdditionalAbiTags, true /*NoFunction*/);
+ const NamedDecl *PrefixND = getClosurePrefix(ND);
+ if (PrefixND && !isCompatibleWith(LangOptions::ClangABI::Ver18))
+ mangleNestedNameWithClosurePrefix(GD, PrefixND, AdditionalAbiTags,
+ true /*NoFunction*/);
+ else
+ mangleNestedName(GD, Context.getEffectiveDeclContext(ND),
+ AdditionalAbiTags, true /*NoFunction*/);
}
} else if (const BlockDecl *BD = dyn_cast<BlockDecl>(D)) {
// Mangle a block in a default parameter; see above explanation for
diff --git a/clang/test/CodeGenCXX/dtor-local-lambda-mangle.cpp
b/clang/test/CodeGenCXX/dtor-local-lambda-mangle.cpp
index 95283dad4a933..bd7b60b816fa7 100644
--- a/clang/test/CodeGenCXX/dtor-local-lambda-mangle.cpp
+++ b/clang/test/CodeGenCXX/dtor-local-lambda-mangle.cpp
@@ -10,7 +10,7 @@ struct E {
E::E() {
struct {
- // CHECK-DAG: _ZTSN1EC13$_012anotherValueMUlvE_E
+ // CHECK-DAG: _ZTSZN1EC1EvEN3$_012anotherValueMUlvE_E
int anotherValue = [x = 1] { return x; }();
} obj;
}
@@ -18,14 +18,14 @@ E::E() {
template<typename T>
E::E(T t) {
struct {
- // CHECK-DAG: _ZTSN1EC1IiEUt_12anotherValueMUlvE_E
+ // CHECK-DAG: _ZTSZN1ED1EvEN3$_012anotherValueMUlvE_E
int anotherValue = [x = 1] { return x; }();
} obj;
}
E::~E() {
struct {
- // CHECK-DAG: _ZTSN1ED13$_012anotherValueMUlvE_E
+ // CHECK-DAG: _ZTSZN1EC1IiEET_ENUt_12anotherValueMUlvE_E
int anotherValue = [x = 2] { return x; }();
} obj;
}
diff --git a/clang/test/CodeGenCXX/mangle-lambdas-gh88906.cpp
b/clang/test/CodeGenCXX/mangle-lambdas-gh88906.cpp
index e7592cec5da77..ba99906d358be 100644
--- a/clang/test/CodeGenCXX/mangle-lambdas-gh88906.cpp
+++ b/clang/test/CodeGenCXX/mangle-lambdas-gh88906.cpp
@@ -21,13 +21,13 @@ void GH88906(){
}
// CHECK-LABEL: define internal void @_ZZ7GH88906vEN4TestC2Ev
-// CHECK: call void @_ZN4funcC2IN7GH889064Test1aMUlvE_ENS3_UlvE0_EEET_T0_
-// CHECK: call void @_ZN4funcC2IN7GH889064Test1bMUlvE_EEET_
-// CHECK: call void @_ZN4funcC2IN7GH889064Test1cMUlvE_EEET_
+// CHECK: call void
@_ZN4funcC2IZ7GH88906vEN4Test1aMUlvE_EZ7GH88906vENS2_UlvE0_EEET_T0_
+// CHECK: call void @_ZN4funcC2IZ7GH88906vEN4Test1bMUlvE_EEET_
+// CHECK: call void @_ZN4funcC2IZ7GH88906vEN4Test1cMUlvE_EEET_
-// CHECK-LABEL: define internal void
@_ZN4funcC2IN7GH889064Test1aMUlvE_ENS3_UlvE0_EEET_T0_
-// CHECK-LABEL: define internal void @_ZN4funcC2IN7GH889064Test1bMUlvE_EEET_
-// CHECK-LABEL: define internal void @_ZN4funcC2IN7GH889064Test1cMUlvE_EEET_
+// CHECK-LABEL: define internal void
@_ZN4funcC2IZ7GH88906vEN4Test1aMUlvE_EZ7GH88906vENS2_UlvE0_EEET_T0_
+// CHECK-LABEL: define internal void @_ZN4funcC2IZ7GH88906vEN4Test1bMUlvE_EEET_
+// CHECK-LABEL: define internal void @_ZN4funcC2IZ7GH88906vEN4Test1cMUlvE_EEET_
// CLANG18-LABEL: define internal void @_ZZ7GH88906vEN4TestC2Ev
// CLANG18: call void
@_ZN4funcC2IZ7GH88906vEN4TestUlvE_EZ7GH88906vENS1_UlvE0_EEET_T0_
diff --git a/clang/test/CodeGenCXX/mangle-lambdas-in-dmi-local-class.cpp
b/clang/test/CodeGenCXX/mangle-lambdas-in-dmi-local-class.cpp
new file mode 100644
index 0000000000000..479ce23dc53ab
--- /dev/null
+++ b/clang/test/CodeGenCXX/mangle-lambdas-in-dmi-local-class.cpp
@@ -0,0 +1,65 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu %s -emit-llvm -I%S -std=c++20 -o -
| FileCheck %s
+
+// Ensure that local classes mangled with <local-name> while mangling a lamda
+// in default member initializer.
+
+// Itanium ABI 5.1.2
+// Names
+// <...> Entities declared within a function, including members of local
classes, are mangled with <local-name>. Entities declared in a namespace or
class scope are mangled with <nested-name>. <...>
+
+#include <typeinfo>
+
+void foo() {
+ {
+ struct Test {
+ const std::type_info& a = typeid([] {});
+ const std::type_info& b = typeid([] {});
+ } T;
+ }
+
+ {
+ struct Test {
+ const std::type_info& a = typeid([] {});
+ const std::type_info& b = typeid([] {});
+ } T;
+ }
+}
+
+// _Z
+// TI
+// Z3foovE ; local-name scope
+// N
+// 4Test
+// 1a ; member a
+// M ; member-initializer context
+// UlvE_ ; lambda closure type
+// E
+
+// CHECK: @_ZTIZ3foovEN4Test1aMUlvE_E
+// CHECK: @_ZTSZ3foovEN4Test1aMUlvE_E
+// CHECK: @_ZTIZ3foovEN4Test1bMUlvE_E
+// CHECK: @_ZTSZ3foovEN4Test1bMUlvE_E
+
+// _Z
+// TI
+// Z3foovE ; local-name scope
+// N
+// 4Test
+// 1a ; member a
+// M ; member-initializer context
+// UlvE_ ; lambda closure type
+// E
+// _0 ; second local 'Test' definition
+
+// CHECK: @_ZTIZ3foovEN4Test1aMUlvE_E_0
+// CHECK: @_ZTSZ3foovEN4Test1aMUlvE_E_0
+// CHECK: @_ZTIZ3foovEN4Test1bMUlvE_E_0
+// CHECK: @_ZTSZ3foovEN4Test1bMUlvE_E_0
+
+// CHECK-LABEL: @_ZZ3foovEN4TestC2Ev
+// CHECK: store ptr @_ZTIZ3foovEN4Test1aMUlvE_E
+// CHECK: store ptr @_ZTIZ3foovEN4Test1bMUlvE_E
+
+// CHECK-LABEL: @_ZZ3foovEN4TestC2E_0v
+// CHECK: store ptr @_ZTIZ3foovEN4Test1aMUlvE_E_0
+// CHECK: store ptr @_ZTIZ3foovEN4Test1bMUlvE_E_0
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