https://github.com/mariusdr updated
https://github.com/llvm/llvm-project/pull/132460
>From d4af25b14fb21f50c3771cce4595ca5c1bb920a7 Mon Sep 17 00:00:00 2001
From: marius doerner <mariu...@users.noreply.github.com>
Date: Fri, 21 Mar 2025 20:19:57 +0100
Subject: [PATCH 1/3] [clang] Placement new error when modifying consts
Raise an error when placement new is used to modify a const-qualified
variable in a constexpr function.
---
clang/lib/AST/ExprConstant.cpp | 9 ++++++
clang/test/AST/ByteCode/placement-new.cpp | 39 +++++++++++++++++++++++
2 files changed, 48 insertions(+)
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 92a28897cf3ee..b4fc3d4471064 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -10415,7 +10415,16 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const
CXXNewExpr *E) {
typedef bool result_type;
bool failed() { return false; }
+ bool checkConst(QualType QT) {
+ if (QT.isConstQualified()) {
+ Info.FFDiag(E, diag::note_constexpr_modify_const_type) << QT;
+ return false;
+ }
+ return true;
+ }
bool found(APValue &Subobj, QualType SubobjType) {
+ if (!checkConst(SubobjType))
+ return false;
// FIXME: Reject the cases where [basic.life]p8 would not permit the
// old name of the object to be used to name the new object.
unsigned SubobjectSize = 1;
diff --git a/clang/test/AST/ByteCode/placement-new.cpp
b/clang/test/AST/ByteCode/placement-new.cpp
index c353162a7aab0..9b12c9f2b1714 100644
--- a/clang/test/AST/ByteCode/placement-new.cpp
+++ b/clang/test/AST/ByteCode/placement-new.cpp
@@ -376,3 +376,42 @@ constexpr int N = [] // expected-error {{must be
initialized by a constant expre
return s.a[0];
}();
#endif
+
+constexpr int modify_const_variable() {
+ const int a = 10;
+ new ((int *)&a) int(12); // both-note {{modification of object of
const-qualified type 'const int' is not allowed in a constant expression}}
+ return a;
+}
+static_assert(modify_const_variable()); // both-error {{not an integral
constant expression}} \
+ // both-note {{in call to}}
+
+typedef const int T0;
+typedef T0 T1;
+constexpr T1 modify_const_variable_td() {
+ T1 a = 10;
+ new ((int *)&a) int(12); // both-note {{modification of object of
const-qualified type 'T1' (aka 'const int') is not allowed in a constant
expression}}
+ return a;
+}
+static_assert(modify_const_variable_td()); // both-error {{not an integral
constant expression}} \
+ // both-note {{in call to}}
+
+template<typename T>
+constexpr T modify_const_variable_tmpl() {
+ T a = 10;
+ new ((int *)&a) int(12); // both-note {{modification of object of
const-qualified type 'const int' is not allowed in a constant expression}}
+ return a;
+}
+static_assert(modify_const_variable_tmpl<const int>()); // both-error {{not an
integral constant expression}} \
+ // both-note {{in call
to}}
+
+namespace ModifyMutableMember {
+ struct S {
+ mutable int a {10};
+ };
+ constexpr int modify_mutable_member() {
+ const S s;
+ new ((int *)&s.a) int(12);
+ return s.a;
+ }
+ static_assert(modify_mutable_member() == 12);
+}
>From 197063860b652ba93ee3baab8b6213bb5dc809de Mon Sep 17 00:00:00 2001
From: marius doerner <mariu...@users.noreply.github.com>
Date: Sun, 23 Mar 2025 09:21:34 +0100
Subject: [PATCH 2/3] Move tests from Ast/Bytecode to SemaCxx
---
clang/test/AST/ByteCode/placement-new.cpp | 39 -------------------
.../SemaCXX/cxx2c-constexpr-placement-new.cpp | 39 +++++++++++++++++++
2 files changed, 39 insertions(+), 39 deletions(-)
diff --git a/clang/test/AST/ByteCode/placement-new.cpp
b/clang/test/AST/ByteCode/placement-new.cpp
index 9b12c9f2b1714..c353162a7aab0 100644
--- a/clang/test/AST/ByteCode/placement-new.cpp
+++ b/clang/test/AST/ByteCode/placement-new.cpp
@@ -376,42 +376,3 @@ constexpr int N = [] // expected-error {{must be
initialized by a constant expre
return s.a[0];
}();
#endif
-
-constexpr int modify_const_variable() {
- const int a = 10;
- new ((int *)&a) int(12); // both-note {{modification of object of
const-qualified type 'const int' is not allowed in a constant expression}}
- return a;
-}
-static_assert(modify_const_variable()); // both-error {{not an integral
constant expression}} \
- // both-note {{in call to}}
-
-typedef const int T0;
-typedef T0 T1;
-constexpr T1 modify_const_variable_td() {
- T1 a = 10;
- new ((int *)&a) int(12); // both-note {{modification of object of
const-qualified type 'T1' (aka 'const int') is not allowed in a constant
expression}}
- return a;
-}
-static_assert(modify_const_variable_td()); // both-error {{not an integral
constant expression}} \
- // both-note {{in call to}}
-
-template<typename T>
-constexpr T modify_const_variable_tmpl() {
- T a = 10;
- new ((int *)&a) int(12); // both-note {{modification of object of
const-qualified type 'const int' is not allowed in a constant expression}}
- return a;
-}
-static_assert(modify_const_variable_tmpl<const int>()); // both-error {{not an
integral constant expression}} \
- // both-note {{in call
to}}
-
-namespace ModifyMutableMember {
- struct S {
- mutable int a {10};
- };
- constexpr int modify_mutable_member() {
- const S s;
- new ((int *)&s.a) int(12);
- return s.a;
- }
- static_assert(modify_mutable_member() == 12);
-}
diff --git a/clang/test/SemaCXX/cxx2c-constexpr-placement-new.cpp
b/clang/test/SemaCXX/cxx2c-constexpr-placement-new.cpp
index a29fb981cedbf..6f6f9b04aa392 100644
--- a/clang/test/SemaCXX/cxx2c-constexpr-placement-new.cpp
+++ b/clang/test/SemaCXX/cxx2c-constexpr-placement-new.cpp
@@ -114,3 +114,42 @@ constexpr bool bleh() {
}
static_assert(bleh()); // expected-error {{not an integral constant
expression}} \
// expected-note {{in call to 'bleh()'}}
+
+constexpr int modify_const_variable() {
+ const int a = 10;
+ new ((int *)&a) int(12); // expected-note {{modification of object of
const-qualified type 'const int' is not allowed in a constant expression}}
+ return a;
+}
+static_assert(modify_const_variable()); // expected-error {{not an integral
constant expression}} \
+ // expected-note {{in call to}}
+
+typedef const int T0;
+typedef T0 T1;
+constexpr T1 modify_const_variable_td() {
+ T1 a = 10;
+ new ((int *)&a) int(12); // expected-note {{modification of object of
const-qualified type 'T1' (aka 'const int') is not allowed in a constant
expression}}
+ return a;
+}
+static_assert(modify_const_variable_td()); // expected-error {{not an integral
constant expression}} \
+ // expected-note {{in call to}}
+
+template<typename T>
+constexpr T modify_const_variable_tmpl() {
+ T a = 10;
+ new ((int *)&a) int(12); // expected-note {{modification of object of
const-qualified type 'const int' is not allowed in a constant expression}}
+ return a;
+}
+static_assert(modify_const_variable_tmpl<const int>()); // expected-error
{{not an integral constant expression}} \
+ // expected-note {{in
call to}}
+
+namespace ModifyMutableMember {
+ struct S {
+ mutable int a {10};
+ };
+ constexpr int modify_mutable_member() {
+ const S s;
+ new ((int *)&s.a) int(12);
+ return s.a;
+ }
+ static_assert(modify_mutable_member() == 12);
+}
>From ad8592bc81f07b93e70e6abd5db2755c84000732 Mon Sep 17 00:00:00 2001
From: marius doerner <mariu...@users.noreply.github.com>
Date: Mon, 24 Mar 2025 18:44:00 +0100
Subject: [PATCH 3/3] Add release notes.
---
clang/docs/ReleaseNotes.rst | 2 ++
1 file changed, 2 insertions(+)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 88862f7661191..62f3302b5e51b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -356,6 +356,8 @@ Bug Fixes to C++ Support
The issue has been addressed by propagating qualifiers during
derived-to-base conversions in the AST. (#GH127824)
- Clang now emits the ``-Wunused-variable`` warning when some structured
bindings are unused
and the ``[[maybe_unused]]`` attribute is not applied. (#GH125810)
+- Clang now issues an error when placement new is used to modify a
const-qualified variable
+ in a ``constexpr`` function. (#GH131432)
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
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