[Clang] Partial implementation of support for P3074 (trivial unions) #146815
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@@ -9543,6 +9543,48 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall( | |
| if (DiagKind == -1) | ||
| return false; | ||
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| if (this->S.Context.getLangOpts().CPlusPlus26 && inUnion() && | ||
| CSM == CXXSpecialMemberKind::Destructor) { | ||
| // [class.dtor]/7 In C++26, a destructor for a union X is only deleted under | ||
| // the additional conditions that: | ||
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| // overload resolution to select a constructor to default-initialize an | ||
| // object of type X either fails or selects a constructor that is either | ||
| // deleted or not trivial, or | ||
| // or X has a variant member V of class type M (or possibly | ||
| // multi-dimensional array thereof) where V has a default member initializer | ||
| // and M has a destructor that is non-trivial, | ||
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| RecordDecl *Parent = Field->getParent(); | ||
| while (Parent && | ||
| (Parent->isAnonymousStructOrUnion() || | ||
| (Parent->isUnion() && Parent->getIdentifier() == nullptr))) { | ||
| if (auto RD = dyn_cast_or_null<RecordDecl>(Parent->getParent())) { | ||
| Parent = RD; | ||
| } else { | ||
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| break; | ||
| } | ||
| } | ||
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| auto ParentDecl = dyn_cast<CXXRecordDecl>(Parent); | ||
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| if (!ParentDecl->isBeingDefined()) { | ||
| Sema::SpecialMemberOverloadResult SMOR = S.LookupSpecialMember( | ||
| ParentDecl, CXXSpecialMemberKind::DefaultConstructor, false, false, | ||
| false, false, false); | ||
| if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Success) { | ||
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Contributor
Author
There was a problem hiding this comment. I'm guessing this is the wrong way to do this, but I don't know how to do it better. Also this doesn't exactly implement the wording I quoted above because the wording is just wrong (see future CWG issue here).
Member
There was a problem hiding this comment. At least when it comes to getting the parent type, we do something similar in
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| CXXConstructorDecl *Ctor = | ||
| dyn_cast<CXXConstructorDecl>(SMOR.getMethod()); | ||
| if (Ctor->isTrivial()) { | ||
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| return false; | ||
| } | ||
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| if (!Ctor->isUserProvided() && !Field->hasInClassInitializer()) { | ||
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| return false; | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| if (Diagnose) { | ||
| if (Field) { | ||
| S.Diag(Field->getLocation(), | ||
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@@ -9696,6 +9738,10 @@ bool SpecialMemberDeletionInfo::shouldDeleteForField(FieldDecl *FD) { | |
| if (inUnion() && shouldDeleteForVariantPtrAuthMember(FD)) | ||
| return true; | ||
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| if (inUnion() && S.Context.getLangOpts().CPlusPlus26 && | ||
| CSM == CXXSpecialMemberKind::DefaultConstructor) | ||
| return false; | ||
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| if (CSM == CXXSpecialMemberKind::DefaultConstructor) { | ||
| // For a default constructor, all references must be initialized in-class | ||
| // and, if a union, it must have a non-const member. | ||
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@@ -9774,7 +9820,8 @@ bool SpecialMemberDeletionInfo::shouldDeleteForField(FieldDecl *FD) { | |
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| // At least one member in each anonymous union must be non-const | ||
| if (CSM == CXXSpecialMemberKind::DefaultConstructor && | ||
| AllVariantFieldsAreConst && !FieldRecord->field_empty() && | ||
| !S.Context.getLangOpts().CPlusPlus26) { | ||
| if (Diagnose) | ||
| S.Diag(FieldRecord->getLocation(), | ||
| diag::note_deleted_default_ctor_all_const) | ||
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@@ -9804,6 +9851,10 @@ bool SpecialMemberDeletionInfo::shouldDeleteForAllConstMembers() { | |
| // default constructor. Don't do that. | ||
| if (CSM == CXXSpecialMemberKind::DefaultConstructor && inUnion() && | ||
| AllFieldsAreConst) { | ||
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| if (S.Context.getLangOpts().CPlusPlus26) | ||
| return false; | ||
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| bool AnyFields = false; | ||
| for (auto *F : MD->getParent()->fields()) | ||
| if ((AnyFields = !F->isUnnamedBitField())) | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,69 @@ | ||
| // RUN: %clang_cc1 -verify -std=c++26 %s -Wno-defaulted-function-deleted -triple x86_64-linux-gnu | ||
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| struct NonTrivial { | ||
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| NonTrivial(int) { } | ||
| ~NonTrivial() { } | ||
| }; | ||
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| union U0 { | ||
| NonTrivial nt; | ||
| int i; | ||
| }; | ||
| U0 u0; | ||
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| // overload resolution to select a constructor to default-initialize an object of type X either fails | ||
| union U1 { | ||
| U1(int); | ||
| NonTrivial nt; // #1 | ||
| }; | ||
| U1 u1(1); // expected-error {{deleted function}} expected-note@#1 {{non-trivial destructor}} | ||
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| // or selects a constructor that is either deleted or not trivial, or | ||
| union U2 { | ||
| U2() : nt(2) { } | ||
| NonTrivial nt; // #2 | ||
| }; | ||
| U2 u2; // expected-error {{deleted function}} expected-note@#2 {{non-trivial destructor}} | ||
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| union U3 { | ||
| U3() = delete; | ||
| U3(int); | ||
| NonTrivial nt; // #3 | ||
| }; | ||
| U3 u3(1); // expected-error {{deleted function}} expected-note@#3 {{non-trivial destructor}} | ||
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| // or X has a variant member V of class type M (or possibly multi-dimensional array thereof) where V has a default member initializer and M has a destructor that is non-trivial, | ||
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| union U4 { | ||
| NonTrivial nt = 1; // #4 | ||
| }; | ||
| U4 u4; // expected-error {{deleted function}} expected-note@#4 {{non-trivial destructor}} | ||
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| union U5 { | ||
| NonTrivial nt; | ||
| U5* next = nullptr; | ||
| }; | ||
| U5 u5; | ||
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| union U6 { | ||
| U6() = default; | ||
| NonTrivial nt; | ||
| U6* next = nullptr; | ||
| }; | ||
| U6 u6; | ||
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| struct DeletedDtor { | ||
| ~DeletedDtor() = delete; // expected-note 2 {{deleted here}} | ||
| }; | ||
| union B1 { | ||
| B1(); | ||
| DeletedDtor a; // expected-note {{because field 'a' has a deleted destructor}} | ||
| }; | ||
| B1 b1; // expected-error {{deleted function}} | ||
| union B2 { | ||
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Member
There was a problem hiding this comment. Some more cases: union A {
struct {
NonTrivial x; // W/ and w/o a default member initialiser.
};
};
A a;
struct B {
union {
NonTrivial x; // as above
};
};
B b;
union {
struct {
union {
struct {
union {
NonTrivial x; // as above
};
};
};
};
} c;
struct {
union {
struct {
union {
struct {
NonTrivial x; // as above
};
};
};
};
} d;
Contributor
Author
There was a problem hiding this comment. Alright I'm not handling this case correctly, but I can't figure out why: union U9 {
struct {
NonTrivial x = 1; // #6
};
} u9; // expected-error {{deleted function}}
Member
There was a problem hiding this comment. Hmm, at a glance nothing jumps out to me; we do create a I did spot a fixme about anonymous unions inside anonymous unions, so er, here’s another gross test case I suppose: union {
union {
NonTrivial x;
};
} a; |
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| B2(); | ||
| union { // expected-note {{deleted destructor}} | ||
| DeletedDtor a; // expected-note {{because field 'a' has a deleted destructor}} | ||
| }; | ||
| }; | ||
| B2 b2; // expected-error {{deleted function}} | ||
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nit (we typically don’t use top-level const for local vars)
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Why not? I see a lot of them btw.
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I thought it was in our coding standards because I’m used to people pointing this out all the time but https://llvm.org/docs/CodingStandards.html doesn’t seem to have anything to say about it.