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const auto & var = ObjectWithSideEffects();
Fixes https://github.com/llvm/llvm-project/issues/54489
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D122661
Files:
clang/lib/Sema/SemaDecl.cpp
clang/test/SemaCXX/warn-unused-variables.cpp
Index: clang/test/SemaCXX/warn-unused-variables.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-variables.cpp
+++ clang/test/SemaCXX/warn-unused-variables.cpp
@@ -154,13 +154,13 @@
#include "Inputs/warn-unused-variables.h"
-namespace arrayRecords {
-
class NonTriviallyDestructible {
public:
~NonTriviallyDestructible() {}
};
+namespace arrayRecords {
+
struct Foo {
int x;
Foo(int x) : x(x) {}
@@ -196,7 +196,7 @@
bar<2>();
}
-}
+} // namespace arrayRecords
#if __cplusplus >= 201103L
namespace with_constexpr {
@@ -250,6 +250,32 @@
template <typename T>
void foo(T &t) {
S s{t};
+ const auto &extended = S{t};
}
}
#endif
+
+// Ensure we do not warn on lifetime extension
+namespace gh54489 {
+
+void f() {
+ const auto &a = NonTriviallyDestructible();
+ const auto &b = a; // expected-warning {{unused variable 'b'}}
+#if __cplusplus >= 201103L
+ const auto &&c = NonTriviallyDestructible();
+ auto &&d = c; // expected-warning {{unused variable 'd'}}
+#endif
+}
+
+struct S {
+ S() = default;
+ S(const S &) = default;
+ S(int);
+};
+
+template <typename T>
+void foo(T &t) {
+ const auto &extended = S{t};
+}
+
+} // namespace gh54489
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -1889,15 +1889,30 @@
// Types of valid local variables should be complete, so this should succeed.
if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
- // White-list anything with an __attribute__((unused)) type.
+ const Expr *Init = VD->getInit();
+ if (const ExprWithCleanups *Cleanups =
+ dyn_cast_or_null<ExprWithCleanups>(Init))
+ Init = Cleanups->getSubExpr();
+
const auto *Ty = VD->getType().getTypePtr();
// Only look at the outermost level of typedef.
if (const TypedefType *TT = Ty->getAs<TypedefType>()) {
+ // White-list anything with an __attribute__((unused)) type.
if (TT->getDecl()->hasAttr<UnusedAttr>())
return false;
}
+ // Warn for reference variables whose initializtion performs lifetime
+ // extension.
+ if (const MaterializeTemporaryExpr *MTE =
+ dyn_cast_or_null<MaterializeTemporaryExpr>(Init)) {
+ if (MTE->getExtendingDecl()) {
+ Ty = VD->getType().getNonReferenceType().getTypePtr();
+ Init = MTE->getSubExpr()->IgnoreImplicitAsWritten();
+ }
+ }
+
// If we failed to complete the type for some reason, or if the type is
// dependent, don't diagnose the variable.
if (Ty->isIncompleteType() || Ty->isDependentType())
@@ -1916,10 +1931,7 @@
if (!RD->hasTrivialDestructor() && !RD->hasAttr<WarnUnusedAttr>())
return false;
- if (const Expr *Init = VD->getInit()) {
- if (const ExprWithCleanups *Cleanups =
- dyn_cast<ExprWithCleanups>(Init))
- Init = Cleanups->getSubExpr();
+ if (Init) {
const CXXConstructExpr *Construct =
dyn_cast<CXXConstructExpr>(Init);
if (Construct && !Construct->isElidable()) {
@@ -1931,10 +1943,16 @@
// Suppress the warning if we don't know how this is constructed, and
// it could possibly be non-trivial constructor.
- if (Init->isTypeDependent())
+ if (Init->isTypeDependent()) {
for (const CXXConstructorDecl *Ctor : RD->ctors())
if (!Ctor->isTrivial())
return false;
+ }
+
+ // Suppress the warning if the constructor is unresolved because
+ // its arguments are dependent.
+ if (isa<CXXUnresolvedConstructExpr>(Init))
+ return false;
}
}
}
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