[clang] 435d084 - [Clang][Sema] Fix incorrect rejection default construction of union with nontrivial member (#82407)
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Mon Oct 6 13:44:09 PDT 2025
Author: Shafik Yaghmour
Date: 2025-10-06T13:44:05-07:00
New Revision: 435d084ed695e7e8d352e22e8b8614b6a022bb04
URL: https://github.com/llvm/llvm-project/commit/435d084ed695e7e8d352e22e8b8614b6a022bb04
DIFF: https://github.com/llvm/llvm-project/commit/435d084ed695e7e8d352e22e8b8614b6a022bb04.diff
LOG: [Clang][Sema] Fix incorrect rejection default construction of union with nontrivial member (#82407)
In 765d8a192180f8f33618087b15c022fe758044af we impelemented a fix for
incorrect deletion of default constructors in unions. This fix missed a
case and so this PR will extend the fix to cover the additional case.
Fixes: https://github.com/llvm/llvm-project/issues/81774
Added:
Modified:
clang/docs/ReleaseNotes.rst
clang/lib/Sema/SemaDeclCXX.cpp
clang/test/CXX/drs/cwg20xx.cpp
clang/test/CodeGen/union-non-trivial-member.cpp
clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 05379f44a0a39..390e0fa7a9a2b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -445,6 +445,8 @@ Bug Fixes to C++ Support
- Correctly deduce return types in ``decltype`` expressions. (#GH160497) (#GH56652) (#GH116319) (#GH161196)
- Fixed a crash in the pre-C++23 warning for attributes before a lambda declarator (#GH161070).
- Fix a crash when attempting to deduce a deduction guide from a non deducible template template parameter. (#130604)
+- Fix for clang incorrectly rejecting the default construction of a union with
+ nontrivial member when another member has an initializer. (#GH81774)
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index d27f76706e5ee..215431ca71310 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -9546,14 +9546,32 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
CXXMethodDecl *Decl = SMOR.getMethod();
FieldDecl *Field = Subobj.dyn_cast<FieldDecl*>();
- int DiagKind = -1;
-
- if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::NoMemberOrDeleted)
- DiagKind = !Decl ? 0 : 1;
- else if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
- DiagKind = 2;
+ enum {
+ NotSet = -1,
+ NoDecl,
+ DeletedDecl,
+ MultipleDecl,
+ InaccessibleDecl,
+ NonTrivialDecl
+ } DiagKind = NotSet;
+
+ if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::NoMemberOrDeleted) {
+ if (CSM == CXXSpecialMemberKind::DefaultConstructor && Field &&
+ Field->getParent()->isUnion()) {
+ // [class.default.ctor]p2:
+ // A defaulted default constructor for class X is defined as deleted if
+ // - X is a union that has a variant member with a non-trivial default
+ // constructor and no variant member of X has a default member
+ // initializer
+ const auto *RD = cast<CXXRecordDecl>(Field->getParent());
+ if (RD->hasInClassInitializer())
+ return false;
+ }
+ DiagKind = !Decl ? NoDecl : DeletedDecl;
+ } else if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
+ DiagKind = MultipleDecl;
else if (!isAccessible(Subobj, Decl))
- DiagKind = 3;
+ DiagKind = InaccessibleDecl;
else if (!IsDtorCallInCtor && Field && Field->getParent()->isUnion() &&
!Decl->isTrivial()) {
// A member of a union must have a trivial corresponding special member.
@@ -9569,13 +9587,13 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
// initializer
const auto *RD = cast<CXXRecordDecl>(Field->getParent());
if (!RD->hasInClassInitializer())
- DiagKind = 4;
+ DiagKind = NonTrivialDecl;
} else {
- DiagKind = 4;
+ DiagKind = NonTrivialDecl;
}
}
- if (DiagKind == -1)
+ if (DiagKind == NotSet)
return false;
if (Diagnose) {
@@ -9593,9 +9611,9 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
<< /*IsObjCPtr*/ false;
}
- if (DiagKind == 1)
+ if (DiagKind == DeletedDecl)
S.NoteDeletedFunction(Decl);
- // FIXME: Explain inaccessibility if DiagKind == 3.
+ // FIXME: Explain inaccessibility if DiagKind == InaccessibleDecl.
}
return true;
diff --git a/clang/test/CXX/drs/cwg20xx.cpp b/clang/test/CXX/drs/cwg20xx.cpp
index 141a1012aef93..bd233bb09522f 100644
--- a/clang/test/CXX/drs/cwg20xx.cpp
+++ b/clang/test/CXX/drs/cwg20xx.cpp
@@ -401,6 +401,15 @@ namespace cwg2083 { // cwg2083: partial
#endif
} // namespace cwg2083
+namespace cwg2084 { // cwg2084: 3.1
+struct S {
+ S();
+};
+union U {
+ S s{}; // cxx98-error {{function definition does not declare parameters}}
+} u;
+} // namespace cwg2084
+
namespace cwg2091 { // cwg2091: 10
template<int &> struct X;
template<int &N> void f(X<N>&);
diff --git a/clang/test/CodeGen/union-non-trivial-member.cpp b/clang/test/CodeGen/union-non-trivial-member.cpp
index fdc9fd16911e1..8b055a9970fc7 100644
--- a/clang/test/CodeGen/union-non-trivial-member.cpp
+++ b/clang/test/CodeGen/union-non-trivial-member.cpp
@@ -15,14 +15,25 @@ union UnionNonTrivial {
non_trivial_constructor b{};
};
+struct Handle {
+ Handle(int) {}
+};
+
+union UnionNonTrivialEqualInit {
+ int NoState = 0;
+ Handle CustomState;
+};
+
void f() {
UnionInt u1;
UnionNonTrivial u2;
+ UnionNonTrivialEqualInit u3;
}
// CHECK: define dso_local void @_Z1fv()
// CHECK: call void @_ZN8UnionIntC1Ev
// CHECK-NEXT: call void @_ZN15UnionNonTrivialC1Ev
+// CHECK-NEXT: call void @_ZN24UnionNonTrivialEqualInitC1Ev
// CHECK: define {{.*}}void @_ZN8UnionIntC1Ev
// CHECK: call void @_ZN8UnionIntC2Ev
@@ -30,8 +41,14 @@ void f() {
// CHECK: define {{.*}}void @_ZN15UnionNonTrivialC1Ev
// CHECK: call void @_ZN15UnionNonTrivialC2Ev
+// CHECK: define {{.*}}void @_ZN24UnionNonTrivialEqualInitC1Ev
+// CHECK: call void @_ZN24UnionNonTrivialEqualInitC2Ev
+
// CHECK: define {{.*}}void @_ZN8UnionIntC2Ev
// CHECK: store i32 1000
// CHECK: define {{.*}}void @_ZN15UnionNonTrivialC2Ev
// CHECK: call void @_ZN23non_trivial_constructorC1Ev
+
+// CHECK: define {{.*}}void @_ZN24UnionNonTrivialEqualInitC2Ev
+// CHECK: store i32 0
diff --git a/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp b/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
index 4bb012f6e4247..1eb7e3a2dea8b 100644
--- a/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
+++ b/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
@@ -188,3 +188,14 @@ static_assert(U2().b.x == 100, "");
static_assert(U3().b.x == 100, "");
} // namespace GH48416
+
+namespace GH81774 {
+struct Handle {
+ Handle(int) {}
+};
+// Should be well-formed because NoState has a brace-or-equal-initializer.
+union a {
+ int NoState = 0;
+ Handle CustomState;
+} b;
+} // namespace GH81774
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