https://github.com/bolshakov-a created https://github.com/llvm/llvm-project/pull/71077
Prior to this, attempts to bind a bit-field to an NTTP of reference type produced an error because references to subobjects in NTTPs are disallowed. But C++20 allows references to subobjects in NTTPs generally (see [P1907R1](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1907r1.html)). Without this change, implementing P1907R1 would cause a bug allowing bit-fields to be bound to reference template arguments. Extracted from https://reviews.llvm.org/D140996 >From 90a0669704b16fb83887058dfe8ce47000282453 Mon Sep 17 00:00:00 2001 From: Bolshakov <bolsh.and...@yandex.ru> Date: Thu, 2 Nov 2023 19:20:27 +0300 Subject: [PATCH] [clang] Improve bit-field in ref NTTP diagnostic Prior to this, attempts to bind a bit-field to an NTTP of reference type produced an error because references to subobjects in NTTPs are disallowed. But C++20 allows references to subobjects in NTTPs generally (see P1907R1). Without this change, implementing P1907R1 would cause a bug allowing bit-fields to be bound to reference template arguments. Extracted from https://reviews.llvm.org/D140996 --- clang/include/clang/Basic/DiagnosticSemaKinds.td | 2 ++ clang/lib/Sema/SemaOverload.cpp | 9 +++++++++ clang/test/CXX/drs/dr12xx.cpp | 2 +- 3 files changed, 12 insertions(+), 1 deletion(-) diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td index 474afc2fb99c1f0..94b836252eda571 100644 --- a/clang/include/clang/Basic/DiagnosticSemaKinds.td +++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td @@ -2251,6 +2251,8 @@ def warn_cxx17_compat_aggregate_init_paren_list : Warning< def err_reference_bind_to_bitfield : Error< "%select{non-const|volatile}0 reference cannot bind to " "bit-field%select{| %1}2">; +def err_reference_bind_to_bitfield_in_cce : Error< + "reference cannot bind to bit-field in converted constant expression">; def err_reference_bind_to_vector_element : Error< "%select{non-const|volatile}0 reference cannot bind to vector element">; def err_reference_bind_to_matrix_element : Error< diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp index d3d2dfed2ce0cc2..36390481e1ce6d4 100644 --- a/clang/lib/Sema/SemaOverload.cpp +++ b/clang/lib/Sema/SemaOverload.cpp @@ -5992,6 +5992,15 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From, /*InOverloadResolution=*/false, /*AllowObjCWritebackConversion=*/false, /*AllowExplicit=*/false); + + // TryCopyInitialization returns incorrect info for attempts to bind reference + // to bit-field due to C++ [over.ics.ref]p4, so check it here. + if (From->refersToBitField() && T.getTypePtr()->isReferenceType()) { + return S.Diag(From->getBeginLoc(), + diag::err_reference_bind_to_bitfield_in_cce) + << From->getSourceRange(); + } + StandardConversionSequence *SCS = nullptr; switch (ICS.getKind()) { case ImplicitConversionSequence::StandardConversion: diff --git a/clang/test/CXX/drs/dr12xx.cpp b/clang/test/CXX/drs/dr12xx.cpp index c23a515ba56cb99..ac28d99784d9c5a 100644 --- a/clang/test/CXX/drs/dr12xx.cpp +++ b/clang/test/CXX/drs/dr12xx.cpp @@ -138,7 +138,7 @@ namespace dr1295 { // dr1295: 4 #if __cplusplus <= 201402L // expected-error@-2 {{does not refer to any declaration}} expected-note@-3 {{here}} #else - // expected-error@-4 {{refers to subobject}} + // expected-error@-4 {{bind to bit-field in converted constant expression}} #endif #if __cplusplus >= 201103L _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
