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[Clang] allow usage of placement new operator in [[msvc::constexpr]] context outside of the std namespace (#119153)

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Fixes #74924
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Oleksandr T. 2024-12-09 18:47:38 +02:00 committed by GitHub
parent 10ef00faf1
commit 1094641bc0
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4 changed files with 28 additions and 3 deletions
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3
clang/docs/ReleaseNotes.rst
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@ -527,6 +527,9 @@ Attribute Changes in Clang
- The ``target_version`` attribute is now only supported for AArch64 and RISC-V architectures.
- Clang now permits the usage of the placement new operator in ``[[msvc::constexpr]]``
context outside of the std namespace. (#GH74924)
Improvements to Clang's diagnostics
-----------------------------------

4
clang/lib/AST/ExprConstant.cpp
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@ -10172,7 +10172,9 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
return false;
IsNothrow = true;
} else if (OperatorNew->isReservedGlobalPlacementOperator()) {
if (Info.CurrentCall->isStdFunction() || Info.getLangOpts().CPlusPlus26) {
if (Info.CurrentCall->isStdFunction() || Info.getLangOpts().CPlusPlus26 ||
(Info.CurrentCall->CanEvalMSConstexpr &&
OperatorNew->hasAttr<MSConstexprAttr>())) {
if (!EvaluatePointer(E->getPlacementArg(0), Result, Info))
return false;
if (Result.Designator.Invalid)

13
clang/test/AST/ms-constexpr-new.cpp Normal file
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@ -0,0 +1,13 @@
// RUN: %clang_cc1 -fms-compatibility -fms-compatibility-version=19.33 -std=c++20 -ast-dump %s | FileCheck %s
// CHECK: used operator new
// CHECK: MSConstexprAttr 0x{{[0-9a-f]+}} <col:17, col:23>
[[nodiscard]] [[msvc::constexpr]] inline void* __cdecl operator new(decltype(sizeof(void*)), void* p) noexcept { return p; }
// CHECK: used constexpr construct_at
// CHECK: AttributedStmt 0x{{[0-9a-f]+}} <col:46, col:88>
// CHECK-NEXT: MSConstexprAttr 0x{{[0-9a-f]+}} <col:48, col:54>
// CHECK-NEXT: ReturnStmt 0x{{[0-9a-f]+}} <col:66, col:88>
constexpr int* construct_at(int* p, int v) { [[msvc::constexpr]] return ::new (p) int(v); }
constexpr bool check_construct_at() { int x; return *construct_at(&x, 42) == 42; }
static_assert(check_construct_at());

11
clang/test/SemaCXX/ms-constexpr-new.cpp
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@ -12,5 +12,12 @@ namespace std {
}
}
constexpr bool check_construct_at() { int x; return *std::construct_at(&x, 42) == 42; }
static_assert(check_construct_at());
constexpr bool check_std_construct_at() { int x; return *std::construct_at(&x, 42) == 42; }
static_assert(check_std_construct_at());
constexpr int* construct_at(int* p, int v) { [[msvc::constexpr]] return ::new (p) int(v); } // unsupported-error {{constexpr function never produces a constant expression}} \
// unsupported-warning {{unknown attribute 'constexpr' ignored}} \
// unsupported-note 2{{this placement new expression is not supported in constant expressions before C++2c}}
constexpr bool check_construct_at() { int x; return *construct_at(&x, 42) == 42; } // unsupported-note {{in call to 'construct_at(&x, 42)'}}
static_assert(check_construct_at()); // unsupported-error {{static assertion expression is not an integral constant expression}}\
// unsupported-note {{in call to 'check_construct_at()'}}