r285872 - [Sema] Allow static_cast<T&&>(e) to check explicit conversions for non-reference-related types.
Eric Fiselier via cfe-commits
cfe-commits at lists.llvm.org
Wed Nov 2 19:13:18 PDT 2016
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);
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