Author: Aaron Ballman Date: 2025-05-15T12:24:12-04:00 New Revision: 0eb4bd27d1ab15ea6b078ac386be01ae13d261a9
URL: https://github.com/llvm/llvm-project/commit/0eb4bd27d1ab15ea6b078ac386be01ae13d261a9 DIFF: https://github.com/llvm/llvm-project/commit/0eb4bd27d1ab15ea6b078ac386be01ae13d261a9.diff LOG: [C] Silence unreachable -Watomic-access diagnostics (#140064) Accessing the member of a structure or union which is _Atomic-qualified is undefined behavior in C. We currently diagnose that with a warning that defaults to an error. In turn, this means we reject a valid program if the access it not reachable because of the error. e.g., if (0) SomeAtomicStruct.Member = 12; // Was diagnosed This silences the diagnostic if the member access is not reachable. Added: Modified: clang/docs/ReleaseNotes.rst clang/lib/Sema/SemaExprMember.cpp clang/test/Sema/atomic-expr.c Removed: ################################################################################ diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index f5ada716d40ec..985cf264876e9 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -533,6 +533,19 @@ Improvements to Clang's diagnostics - A new off-by-default warning ``-Wms-bitfield-padding`` has been added to alert to cases where bit-field packing may diff er under the MS struct ABI (#GH117428). +- ``-Watomic-access`` no longer fires on unreachable code. e.g., + + .. code-block:: c + + _Atomic struct S { int a; } s; + void func(void) { + if (0) + s.a = 12; // Previously diagnosed with -Watomic-access, now silenced + s.a = 12; // Still diagnosed with -Watomic-access + return; + s.a = 12; // Previously diagnosed, now silenced + } + - A new ``-Wcharacter-conversion`` warns where comparing or implicitly converting between diff erent Unicode character types (``char8_t``, ``char16_t``, ``char32_t``). diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp index 053414ff7a1a7..39c162c3b835d 100644 --- a/clang/lib/Sema/SemaExprMember.cpp +++ b/clang/lib/Sema/SemaExprMember.cpp @@ -1385,7 +1385,7 @@ static ExprResult LookupMemberExpr(Sema &S, LookupResult &R, // lvalue. Because this is inherently unsafe as an atomic operation, the // warning defaults to an error. if (const auto *ATy = BaseType->getAs<AtomicType>()) { - S.DiagRuntimeBehavior(OpLoc, nullptr, + S.DiagRuntimeBehavior(OpLoc, BaseExpr.get(), S.PDiag(diag::warn_atomic_member_access)); BaseType = ATy->getValueType().getUnqualifiedType(); BaseExpr = ImplicitCastExpr::Create( diff --git a/clang/test/Sema/atomic-expr.c b/clang/test/Sema/atomic-expr.c index 7e5219dd3f14a..96571e3e68c87 100644 --- a/clang/test/Sema/atomic-expr.c +++ b/clang/test/Sema/atomic-expr.c @@ -114,6 +114,23 @@ void func_16(void) { (void)sizeof(xp->val); (void)sizeof(y.ival); (void)sizeof(yp->ival); + + // Also, do not diagnose in unreachable code paths. + { + if (0) { + x.val = 12; + xp->val = 12; + (void)y.ival; + (void)yp->ival; + } + + return; + + x.val = 12; + xp->val = 12; + (void)y.ival; + (void)yp->ival; + } } // Ensure that we correctly implement assignment constraints from C2x 6.5.16.1. _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
