Mordante created this revision.
Mordante added a reviewer: rsmith.
Mordante added a project: clang.
The overload resolution for enums with a fixed underlaying type has changed in
the C++14 standard. This patch implements the new rule.
Note: I don't have access to the CWG 1601 paper, but based on
https://en.cppreference.com/w/cpp/language/overload_resolution I applied the
fix retroactively to C++11.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D65695
Files:
clang/lib/Sema/SemaOverload.cpp
clang/test/CXX/drs/dr16xx.cpp
clang/test/CXX/drs/dr6xx.cpp
clang/www/cxx_dr_status.html
Index: clang/www/cxx_dr_status.html
===================================================================
--- clang/www/cxx_dr_status.html
+++ clang/www/cxx_dr_status.html
@@ -9421,7 +9421,7 @@
<td><a href="http://wg21.link/cwg1601";>1601</a></td>
<td>C++14</td>
<td>Promotion of enumeration with fixed underlying type</td>
- <td class="none" align="center">Unknown</td>
+ <td class="svn" align="center">SVN (C++11 onwards)</td>
</tr>
<tr class="open" id="1602">
<td><a href="http://wg21.link/cwg1602";>1602</a></td>
Index: clang/test/CXX/drs/dr6xx.cpp
===================================================================
--- clang/test/CXX/drs/dr6xx.cpp
+++ clang/test/CXX/drs/dr6xx.cpp
@@ -1007,9 +1007,10 @@
void j(long); // expected-note {{candidate}}
int d = j(g); // expected-error {{ambiguous}}
- int k(short); // expected-note {{candidate}}
- void k(int); // expected-note {{candidate}}
- int x = k(g); // expected-error {{ambiguous}}
+ // Valid per dr1601
+ int k(short);
+ void k(int);
+ int x = k(g);
}
#endif
Index: clang/test/CXX/drs/dr16xx.cpp
===================================================================
--- clang/test/CXX/drs/dr16xx.cpp
+++ clang/test/CXX/drs/dr16xx.cpp
@@ -23,6 +23,17 @@
} // std
#endif
+namespace dr1601 { // dr1601
+#if __cplusplus >= 201103L
+enum E : char { e };
+void f(char);
+void f(int);
+void g() {
+ f(e);
+}
+#endif
+} // namespace dr1601
+
namespace dr1611 { // dr1611: dup 1658
struct A { A(int); };
struct B : virtual A { virtual void f() = 0; };
Index: clang/lib/Sema/SemaOverload.cpp
===================================================================
--- clang/lib/Sema/SemaOverload.cpp
+++ clang/lib/Sema/SemaOverload.cpp
@@ -3751,6 +3751,26 @@
!SCS2.IsLvalueReference && SCS2.BindsToFunctionLvalue);
}
+/// Returns the underlaying type of a fixed enum of the \a SCS's @c FromType
+/// if the \a SCS uses an integral promotion. Upon failure an empty type is
+/// returned.
+static QualType
+getFixedEnumUnderlayingType(const StandardConversionSequence &SCS) {
+
+ if (SCS.Second != ICK_Integral_Promotion)
+ return QualType();
+
+ QualType FromType = SCS.getFromType();
+ if (!FromType->isEnumeralType())
+ return QualType();
+
+ EnumDecl *Enum = FromType->getAs<EnumType>()->getDecl();
+ if (!Enum->isFixed())
+ return QualType();
+
+ return Enum->getIntegerType();
+}
+
/// CompareStandardConversionSequences - Compare two standard
/// conversion sequences to determine whether one is better than the
/// other or if they are indistinguishable (C++ 13.3.3.2p3).
@@ -3792,6 +3812,23 @@
? ImplicitConversionSequence::Better
: ImplicitConversionSequence::Worse;
+ // C++14 [over.ics.rank]p4b2:
+ // This is retroactively applied to C++11 by CWG 1601.
+ //
+ // A conversion that promotes an enumeration whose underlying type is fixed
+ // to its underlying type is better than one that promotes to the promoted
+ // underlying type, if the two are different.
+ QualType UnderlayingType1 = getFixedEnumUnderlayingType(SCS1);
+ QualType UnderlayingType2 = getFixedEnumUnderlayingType(SCS2);
+ if (!UnderlayingType1.isNull() && !UnderlayingType2.isNull()) {
+ if (SCS1.getToType(1) == UnderlayingType1 &&
+ SCS2.getToType(1) != UnderlayingType2)
+ return ImplicitConversionSequence::Better;
+ else if (SCS1.getToType(1) != UnderlayingType1 &&
+ SCS2.getToType(1) == UnderlayingType2)
+ return ImplicitConversionSequence::Worse;
+ }
+
// C++ [over.ics.rank]p4b2:
//
// If class B is derived directly or indirectly from class A,
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