https://github.com/AZero13 updated https://github.com/llvm/llvm-project/pull/207616
>From 867eb3388d90f039be72ec30cbefe991b6f60e9e Mon Sep 17 00:00:00 2001 From: AZero13 <[email protected]> Date: Sun, 5 Jul 2026 17:50:56 -0400 Subject: [PATCH 1/2] [clang][SemaCXX] Fix crash when using static_cast to _Atomic types in C++ This PR fixes a compiler crash (assertion failure) in both the constant evaluator (ExprConstant.cpp) and LLVM CodeGen (CGExprAgg.cpp) when evaluating a static_cast to an _Atomic type in C++. When evaluating casts, CastOperation::CastOperation in was unconditionally stripping the _Atomic qualifier from the destination type using getAtomicUnqualifiedType(). This behavior is correct for C23 (under C23 6.5.4p6, where cast expressions yield the non-atomic version of the type), but it is incorrect for C++ where _Atomic(T) is treated as a distinct type wrapper. Modify CastOperation::CastOperation to only strip the _Atomic qualifier in C mode. In C++ mode, we preserve the _Atomic wrapper, ensuring that InitializationSequence properly evaluates the target type as _Atomic(T) and adds the implicit CK_NonAtomicToAtomic conversion step. Fixes #207610. --- clang/lib/Sema/SemaCast.cpp | 8 +++++++- clang/test/SemaCXX/atomic-type.cpp | 9 +++++++++ 2 files changed, 16 insertions(+), 1 deletion(-) diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp index 133837623a7a6..0d0b20a4395f2 100644 --- a/clang/lib/Sema/SemaCast.cpp +++ b/clang/lib/Sema/SemaCast.cpp @@ -78,7 +78,13 @@ namespace { // the qualifier. if (!S.Context.getLangOpts().ObjC && !DestType->isRecordType() && !DestType->isArrayType() && !DestType.getPointerAuth()) { - DestType = DestType.getAtomicUnqualifiedType(); + if (S.Context.getLangOpts().CPlusPlus) { + // Note that in C++, _Atomic(T) is a distinct type, not a + // cv-qualifier, so it is not stripped. + DestType = DestType.getUnqualifiedType(); + } else { + DestType = DestType.getAtomicUnqualifiedType(); + } } if (const BuiltinType *placeholder = diff --git a/clang/test/SemaCXX/atomic-type.cpp b/clang/test/SemaCXX/atomic-type.cpp index 3200a59bc86a2..b8f8f184da643 100644 --- a/clang/test/SemaCXX/atomic-type.cpp +++ b/clang/test/SemaCXX/atomic-type.cpp @@ -111,3 +111,12 @@ namespace non_trivially_copyable { _Atomic S s; // expected-error {{_Atomic cannot be applied to type 'S' which is not trivially copyable}} \ // expected-warning {{'_Atomic' is a C11 extension}} } + +namespace static_cast_crash { + struct S { char a; }; + void static_cast_non_atomic_to_atomic() { + _Atomic struct S a; // expected-warning {{'_Atomic' is a C11 extension}} + a = static_cast<_Atomic(struct S)>(S()); // expected-warning {{'_Atomic' is a C11 extension}} + } +} + >From d0b0415a91545a57d1d9ba0cd3b49e0097cdd03f Mon Sep 17 00:00:00 2001 From: AZero13 <[email protected]> Date: Mon, 6 Jul 2026 14:54:36 -0400 Subject: [PATCH 2/2] Update SemaCast.cpp --- clang/lib/Sema/SemaCast.cpp | 3 +++ 1 file changed, 3 insertions(+) diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp index 0d0b20a4395f2..86b5a337c6f8b 100644 --- a/clang/lib/Sema/SemaCast.cpp +++ b/clang/lib/Sema/SemaCast.cpp @@ -85,6 +85,9 @@ namespace { } else { DestType = DestType.getAtomicUnqualifiedType(); } + + // Ensure ResultType matches the stripped DestType (e.g., dropping _Atomic in C) + ResultType = DestType.getNonLValueExprType(S.Context); } if (const BuiltinType *placeholder = _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
