[clang] 26baa00 - [clang] Diagnose dangling references for parenthesized aggregate initialization. (#117690)
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Fri Nov 29 01:15:23 PST 2024
Author: Haojian Wu
Date: 2024-11-29T10:15:19+01:00
New Revision: 26baa00908b2eb8b2925800af6bc64fbe53cac48
URL: https://github.com/llvm/llvm-project/commit/26baa00908b2eb8b2925800af6bc64fbe53cac48
DIFF: https://github.com/llvm/llvm-project/commit/26baa00908b2eb8b2925800af6bc64fbe53cac48.diff
LOG: [clang] Diagnose dangling references for parenthesized aggregate initialization. (#117690)
Unlike brace initialization, the parenthesized aggregate initialization
in C++20 does not extend the lifetime of a temporary object bound to a
reference in an aggreate. This can lead to dangling references:
```
struct A { const int& r; };
A a1(1); // well-formed, but results in a dangling reference.
```
With this patch, clang will diagnose this common dangling issues.
Fixes #101957
Added:
clang/test/SemaCXX/cxx20-warn-dangling-paren-list-agg-init.cpp
Modified:
clang/docs/ReleaseNotes.rst
clang/lib/Sema/CheckExprLifetime.cpp
clang/test/AST/ByteCode/records.cpp
clang/test/SemaCXX/paren-list-agg-init.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 102ffb56fec35f..9882a1c42d50c4 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -627,6 +627,8 @@ Improvements to Clang's diagnostics
- Clang now supports using alias templates in deduction guides, aligning with the C++ standard,
which treats alias templates as synonyms for their underlying types (#GH54909).
+- Clang now diagnoses dangling references for C++20's parenthesized aggregate initialization (#101957).
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index de69d6537b5692..15ceff873693a5 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -204,6 +204,7 @@ struct IndirectLocalPathEntry {
GslPointerInit,
GslPointerAssignment,
DefaultArg,
+ ParenAggInit,
} Kind;
Expr *E;
union {
@@ -985,6 +986,17 @@ static void visitLocalsRetainedByInitializer(IndirectLocalPath &Path,
if (isa<CallExpr>(Init) || isa<CXXConstructExpr>(Init))
return visitFunctionCallArguments(Path, Init, Visit);
+ if (auto *CPE = dyn_cast<CXXParenListInitExpr>(Init)) {
+ RevertToOldSizeRAII RAII(Path);
+ Path.push_back({IndirectLocalPathEntry::ParenAggInit, CPE});
+ for (auto *I : CPE->getInitExprs()) {
+ if (I->isGLValue())
+ visitLocalsRetainedByReferenceBinding(Path, I, RK_ReferenceBinding,
+ Visit);
+ else
+ visitLocalsRetainedByInitializer(Path, I, Visit, true);
+ }
+ }
switch (Init->getStmtClass()) {
case Stmt::UnaryOperatorClass: {
auto *UO = cast<UnaryOperator>(Init);
@@ -1081,6 +1093,7 @@ static SourceRange nextPathEntryRange(const IndirectLocalPath &Path, unsigned I,
case IndirectLocalPathEntry::GslReferenceInit:
case IndirectLocalPathEntry::GslPointerInit:
case IndirectLocalPathEntry::GslPointerAssignment:
+ case IndirectLocalPathEntry::ParenAggInit:
// These exist primarily to mark the path as not permitting or
// supporting lifetime extension.
break;
@@ -1392,6 +1405,7 @@ checkExprLifetimeImpl(Sema &SemaRef, const InitializedEntity *InitEntity,
switch (Elem.Kind) {
case IndirectLocalPathEntry::AddressOf:
case IndirectLocalPathEntry::LValToRVal:
+ case IndirectLocalPathEntry::ParenAggInit:
// These exist primarily to mark the path as not permitting or
// supporting lifetime extension.
break;
diff --git a/clang/test/AST/ByteCode/records.cpp b/clang/test/AST/ByteCode/records.cpp
index 2eeaafc04c516c..4601aface135ee 100644
--- a/clang/test/AST/ByteCode/records.cpp
+++ b/clang/test/AST/ByteCode/records.cpp
@@ -1015,11 +1015,13 @@ namespace ParenInit {
};
/// Not constexpr!
- O o1(0);
+ O o1(0); // both-warning {{temporary whose address is used as value of}}
+ // FIXME: the secondary warning message is bogus, would be nice to suppress it.
constinit O o2(0); // both-error {{variable does not have a constant initializer}} \
// both-note {{required by 'constinit' specifier}} \
// both-note {{reference to temporary is not a constant expression}} \
- // both-note {{temporary created here}}
+ // both-note {{temporary created here}} \
+ // both-warning {{temporary whose address is used as value}}
/// Initializing an array.
diff --git a/clang/test/SemaCXX/cxx20-warn-dangling-paren-list-agg-init.cpp b/clang/test/SemaCXX/cxx20-warn-dangling-paren-list-agg-init.cpp
new file mode 100644
index 00000000000000..645a7caba714e2
--- /dev/null
+++ b/clang/test/SemaCXX/cxx20-warn-dangling-paren-list-agg-init.cpp
@@ -0,0 +1,59 @@
+// RUN: %clang_cc1 -verify -std=c++20 %s -fsyntax-only
+
+namespace std {
+template <class T> struct remove_reference { typedef T type; };
+template <class T> struct remove_reference<T&> { typedef T type; };
+template <class T> struct remove_reference<T&&> { typedef T type; };
+
+template <class T> typename remove_reference<T>::type &&move(T &&t);
+} // namespace std
+
+// dcl.init 16.6.2.2
+struct A {
+ int a;
+ int&& r;
+};
+
+int f();
+int n = 10;
+
+A a1{1, f()}; // OK, lifetime is extended for direct-list-initialization
+// well-formed, but dangling reference
+A a2(1, f()); // expected-warning {{temporary whose address is used as value}}
+// well-formed, but dangling reference
+A a4(1.0, 1); // expected-warning {{temporary whose address is used as value}}
+A a5(1.0, std::move(n)); // OK
+
+
+
+struct B {
+ const int& r;
+};
+B test(int local) {
+ return B(1); // expected-warning {{returning address}}
+ return B(local); // expected-warning {{address of stack memory}}
+}
+
+void f(B b);
+void test2(int local) {
+ // No diagnostic on the following cases where both the aggregate object and
+ // temporary end at the end of the full expression.
+ f(B(1));
+ f(B(local));
+}
+
+// Test nested struct.
+struct C {
+ B b;
+};
+
+struct D {
+ C c;
+};
+
+C c1(B(
+ 1 // expected-warning {{temporary whose address is used as value}}
+));
+D d1(C(B(
+ 1 // expected-warning {{temporary whose address is used as value}}
+)));
diff --git a/clang/test/SemaCXX/paren-list-agg-init.cpp b/clang/test/SemaCXX/paren-list-agg-init.cpp
index cc2a9d88dd4a6e..61afba85e1dff9 100644
--- a/clang/test/SemaCXX/paren-list-agg-init.cpp
+++ b/clang/test/SemaCXX/paren-list-agg-init.cpp
@@ -116,6 +116,7 @@ void foo(int n) { // expected-note {{declared here}}
B b2(A(1), {}, 1);
// beforecxx20-warning at -1 {{aggregate initialization of type 'A' from a parenthesized list of values is a C++20 extension}}
// beforecxx20-warning at -2 {{aggregate initialization of type 'B' from a parenthesized list of values is a C++20 extension}}
+ // expected-warning at -3 {{temporary whose address is used as value of local variable 'b2' will be destroyed at the end of the full-expression}}
C c(A(1), 1, 2, 3, 4);
// expected-error at -1 {{array initializer must be an initializer list}}
@@ -262,9 +263,12 @@ struct O {
O o1(0, 0, 0); // no-error
// beforecxx20-warning at -1 {{aggregate initialization of type 'O' from a parenthesized list of values is a C++20 extension}}
+// expected-warning at -2 {{temporary whose address is used as value of local variable 'o1' will be destroyed at the end of the full-expression}}
+// expected-warning at -3 {{temporary whose address is used as value of local variable 'o1' will be destroyed at the end of the full-expression}}
O o2(0, 0); // no-error
// beforecxx20-warning at -1 {{aggregate initialization of type 'O' from a parenthesized list of values is a C++20 extension}}
+// expected-warning at -2 {{temporary whose address is used as value of local variable 'o2' will be destroyed at the end of the full-expression}}
O o3(0);
// expected-error at -1 {{reference member of type 'int &&' uninitialized}}
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