[Clang] Only ignore special methods for unused private fields in BuildFieldReferenceExpr #116965
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@llvm/pr-subscribers-clang Author: Mészáros Gergely (Maetveis) ChangesThe original code assumed that only special methods might be defined as defaulted. Since C++20 comparison operators might be defaulted too, and we do want to consider those as using the fields of the class. Fixes: #116961 Full diff: https://github.com/llvm/llvm-project/pull/116965.diff 2 Files Affected:
diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index c32df607692813..46821dc8746b2a 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -1874,8 +1874,16 @@ Sema::BuildFieldReferenceExpr(Expr *BaseExpr, bool IsArrow,
Context.getAttributedType(attr::NoDeref, MemberType, MemberType);
}
- auto *CurMethod = dyn_cast<CXXMethodDecl>(CurContext);
- if (!(CurMethod && CurMethod->isDefaulted()))
+ auto isDefaultedSpecialMember = [this](const DeclContext *Ctx) {
+ auto *Method = dyn_cast<CXXMethodDecl>(CurContext);
+ if (!Method || !Method->isDefaulted())
+ return false;
+
+ return getDefaultedFunctionKind(Method).isSpecialMember();
+ };
+
+ // Implicit special members should not mark fields as used.
+ if (!isDefaultedSpecialMember(CurContext))
UnusedPrivateFields.remove(Field);
ExprResult Base = PerformObjectMemberConversion(BaseExpr, SS.getScopeRep(),
diff --git a/clang/test/SemaCXX/warn-unused-private-field.cpp b/clang/test/SemaCXX/warn-unused-private-field.cpp
index 1128eacc309d9f..9913dbaafb7a57 100644
--- a/clang/test/SemaCXX/warn-unused-private-field.cpp
+++ b/clang/test/SemaCXX/warn-unused-private-field.cpp
@@ -20,6 +20,20 @@ class SpaceShipDefaultCompare {
int operator<=>(const SpaceShipDefaultCompare &) const = default;
};
+class EqDefaultCompareOutOfClass {
+ int used;
+ bool operator==(const EqDefaultCompareOutOfClass &) const;
+};
+
+bool EqDefaultCompareOutOfClass::operator==(const EqDefaultCompareOutOfClass &) const = default;
+
+class FriendEqDefaultCompareOutOfClass {
+ int used;
+ friend bool operator==(const FriendEqDefaultCompareOutOfClass &, const FriendEqDefaultCompareOutOfClass &);
+};
+
+bool operator==(const FriendEqDefaultCompareOutOfClass &, const FriendEqDefaultCompareOutOfClass &) = default;
+
#endif
class NotFullyDefined {
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erichkeane
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Nov 25, 2024
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Needs a release note, else LGTM.
…dFieldReferenceExpr The original code assumed that only special methods might be defined as defaulted. Since C++20 comparison operators might be defaulted too, and we *do* want to consider those as using the fields of the class. Fixes: llvm#116961
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| }; | ||
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| class EqDefaultCompareOutOfClass { | ||
| int used; // no warning |
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Please explain a touch better with 'no warning'? Something like, "Test to ensure that the defaulted operator results in this being seen as 'used' despite there not being code to do so."?
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Okay, sorry I wasn't sure what you were referring to, but I get now that from the change-set it is not obvious how / why the issue in #116961 is fixed, and why it is a special case not covered by the current testing. I expanded quite a bit on the comment, hopefully it did not become too verbose now.
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The original code assumed that only special methods might be defined as defaulted. Since C++20 comparison operators might be defaulted too, and we do want to consider those as using the fields of the class.
Fixes: #116961