Author: ericwf Date: Wed Nov 2 21:13:17 2016 New Revision: 285872 URL: http://llvm.org/viewvc/llvm-project?rev=285872&view=rev Log: [Sema] Allow static_cast<T&&>(e) to check explicit conversions for non-reference-related types.
Summary: [expr.cast.static] states: > 3. A glvalue of type “cv1 T1” can be cast to type “rvalue reference to cv2 > T2” if “cv2 T2” is reference-compatible > with “cv1 T1”. The result refers to the object or the specified base class > subobject thereof. If T2 is > an inaccessible or ambiguous base class of T1, a program that necessitates > such a cast is > ill-formed. > > 4. Otherwise, an expression e can be explicitly converted to a type T using a > static_cast of the form static_- > cast<T>(e) if the declaration T t(e); is well-formed, for some invented > temporary variable t. [...] Currently when checking p3 Clang will diagnose `static_cast<T&&>(e)` as invalid if the argument is not reference compatible with `T`. However I believe the correct behavior is to also check p4 in those cases. For example: ``` double y = 42; static_cast<int&&>(y); // this should be OK. 'int&& t(y)' is well formed ``` Note that we still don't check p4 for non-reference-compatible types which are reference-related since `T&& t(e);` should never be well formed in those cases. Reviewers: rsmith Subscribers: cfe-commits Differential Revision: https://reviews.llvm.org/D26231 Added: cfe/trunk/test/CXX/expr/expr.post/expr.static.cast/p3-p4-0x.cpp Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td cfe/trunk/lib/Sema/SemaCast.cpp cfe/trunk/test/SemaCXX/rval-references.cpp Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=285872&r1=285871&r2=285872&view=diff ============================================================================== --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original) +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Wed Nov 2 21:13:17 2016 @@ -5944,6 +5944,9 @@ def err_bad_cxx_cast_vector_to_vector_di def err_bad_lvalue_to_rvalue_cast : Error< "cannot cast from lvalue of type %1 to rvalue reference type %2; types are " "not compatible">; +def err_bad_rvalue_to_rvalue_cast : Error< + "cannot cast from rvalue of type %1 to rvalue reference type %2; types are " + "not compatible">; def err_bad_static_cast_pointer_nonpointer : Error< "cannot cast from type %1 to pointer type %2">; def err_bad_static_cast_member_pointer_nonmp : Error< Modified: cfe/trunk/lib/Sema/SemaCast.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaCast.cpp?rev=285872&r1=285871&r2=285872&view=diff ============================================================================== --- cfe/trunk/lib/Sema/SemaCast.cpp (original) +++ cfe/trunk/lib/Sema/SemaCast.cpp Wed Nov 2 21:13:17 2016 @@ -983,7 +983,7 @@ static TryCastResult TryStaticCast(Sema // C++11 [expr.static.cast]p3: // A glvalue of type "cv1 T1" can be cast to type "rvalue reference to cv2 // T2" if "cv2 T2" is reference-compatible with "cv1 T1". - tcr = TryLValueToRValueCast(Self, SrcExpr.get(), DestType, CStyle, Kind, + tcr = TryLValueToRValueCast(Self, SrcExpr.get(), DestType, CStyle, Kind, BasePath, msg); if (tcr != TC_NotApplicable) return tcr; @@ -1134,12 +1134,12 @@ static TryCastResult TryStaticCast(Sema } /// Tests whether a conversion according to N2844 is valid. -TryCastResult -TryLValueToRValueCast(Sema &Self, Expr *SrcExpr, QualType DestType, - bool CStyle, CastKind &Kind, CXXCastPath &BasePath, - unsigned &msg) { +TryCastResult TryLValueToRValueCast(Sema &Self, Expr *SrcExpr, + QualType DestType, bool CStyle, + CastKind &Kind, CXXCastPath &BasePath, + unsigned &msg) { // C++11 [expr.static.cast]p3: - // A glvalue of type "cv1 T1" can be cast to type "rvalue reference to + // A glvalue of type "cv1 T1" can be cast to type "rvalue reference to // cv2 T2" if "cv2 T2" is reference-compatible with "cv1 T1". const RValueReferenceType *R = DestType->getAs<RValueReferenceType>(); if (!R) @@ -1160,15 +1160,18 @@ TryLValueToRValueCast(Sema &Self, Expr * FromType = FromType.getUnqualifiedType(); ToType = ToType.getUnqualifiedType(); } - - if (Self.CompareReferenceRelationship(SrcExpr->getLocStart(), - ToType, FromType, - DerivedToBase, ObjCConversion, - ObjCLifetimeConversion) - != Sema::Ref_Compatible) { - if (CStyle) + + Sema::ReferenceCompareResult RefResult = Self.CompareReferenceRelationship( + SrcExpr->getLocStart(), ToType, FromType, DerivedToBase, ObjCConversion, + ObjCLifetimeConversion); + if (RefResult != Sema::Ref_Compatible) { + if (CStyle || RefResult == Sema::Ref_Incompatible) return TC_NotApplicable; - msg = diag::err_bad_lvalue_to_rvalue_cast; + // Diagnose types which are reference-related but not compatible here since + // we can provide better diagnostics. In these cases forwarding to + // [expr.static.cast]p4 should never result in a well-formed cast. + msg = SrcExpr->isLValue() ? diag::err_bad_lvalue_to_rvalue_cast + : diag::err_bad_rvalue_to_rvalue_cast; return TC_Failed; } Added: cfe/trunk/test/CXX/expr/expr.post/expr.static.cast/p3-p4-0x.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/expr/expr.post/expr.static.cast/p3-p4-0x.cpp?rev=285872&view=auto ============================================================================== --- cfe/trunk/test/CXX/expr/expr.post/expr.static.cast/p3-p4-0x.cpp (added) +++ cfe/trunk/test/CXX/expr/expr.post/expr.static.cast/p3-p4-0x.cpp Wed Nov 2 21:13:17 2016 @@ -0,0 +1,43 @@ +// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s + + +// p3 +// A glvalue of type "cv1 T1" can be cast to type "rvalue reference to +// cv2 T2" if "cv2 T2" is reference-compatible with "cv1 T1" (8.5.3). +// p4 +// Otherwise, an expression e can be explicitly converted to a type T using a +// static_cast of the form static_cast<T>(e) if the declaration T t(e); is +// well-formed, for some invented temporary variable t (8.5). [...] +struct A { }; +struct B : A { }; + +struct C { explicit operator A&&(); }; +struct D { operator B(); }; + +template<typename T> T& lvalue(); +template<typename T> T&& xvalue(); +template <typename T> T prvalue(); + +void test(A &a, B &b) { + A &&ar0 = static_cast<A&&>(prvalue<A>()); + A &&ar1 = static_cast<A&&>(prvalue<B>()); + A &&ar2 = static_cast<A&&>(lvalue<C>()); + A &&ar3 = static_cast<A&&>(xvalue<C>()); + A &&ar4 = static_cast<A&&>(prvalue<C>()); + A &&ar5 = static_cast<A&&>(lvalue<D>()); + A &&ar6 = static_cast<A&&>(xvalue<D>()); + A &&ar7 = static_cast<A&&>(prvalue<D>()); + + A &&ar8 = static_cast<A&&>(prvalue<const A>()); // expected-error {{binding value of type 'const A' to reference to type 'A' drops 'const' qualifier}} + A &&ar9 = static_cast<A&&>(lvalue<const A>()); // expected-error {{cannot cast from lvalue of type 'const A'}} + A &&ar10 = static_cast<A&&>(xvalue<const A>()); // expected-error {{cannot cast from rvalue of type 'const A'}} + + const A &&ar11 = static_cast<const A&&>(prvalue<A>()); + const A &&ar12 = static_cast<const A&&>(prvalue<B>()); + const A &&ar13 = static_cast<const A&&>(lvalue<C>()); + const A &&ar14 = static_cast<const A&&>(xvalue<C>()); + const A &&ar15 = static_cast<const A&&>(prvalue<C>()); + const A &&ar16 = static_cast<const A&&>(lvalue<D>()); + + const A &&ar17 = static_cast<const A&&>(prvalue<A const volatile>()); // expected-error {{binding value of type 'const volatile A' to reference to type 'const A' drops 'volatile' qualifier}} +} Modified: cfe/trunk/test/SemaCXX/rval-references.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/rval-references.cpp?rev=285872&r1=285871&r2=285872&view=diff ============================================================================== --- cfe/trunk/test/SemaCXX/rval-references.cpp (original) +++ cfe/trunk/test/SemaCXX/rval-references.cpp Wed Nov 2 21:13:17 2016 @@ -1,4 +1,4 @@ -// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++11 %s +// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++11 %s typedef int&& irr; typedef irr& ilr_c1; // Collapses to int& @@ -30,11 +30,15 @@ void f() { int &&virr2 = 0; int &&virr3 = virr2; // expected-error {{rvalue reference to type 'int' cannot bind to lvalue of type 'int'}} int i1 = 0; + const double d1 = 0; + const int ci1 = 1; int &&virr4 = i1; // expected-error {{rvalue reference to type 'int' cannot bind to lvalue of type 'int'}} int &&virr5 = ret_irr(); int &&virr6 = static_cast<int&&>(i1); - (void)static_cast<not_int&&>(i1); // expected-error {{types are not compatible}} - + (void)static_cast<not_int &&>(i1); // expected-error {{reference to type 'not_int' could not bind to an lvalue of type 'int'}} + (void)static_cast<int &&>(static_cast<int const&&>(i1)); // expected-error {{cannot cast from rvalue of type 'const int' to rvalue reference type 'int &&'}} + (void)static_cast<int &&>(ci1); // expected-error {{types are not compatible}} + (void)static_cast<int &&>(d1); int i2 = over(i1); not_int ni1 = over(0); int i3 = over(virr2); _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
