[PATCH] D17451: PR26448: [Sema] Fix determined type of ternary operator acting on two xvalue class types

[Erik Pilkington via cfe-commits]

erik.pilkington created this revision.
erik.pilkington added a reviewer: rsmith.
erik.pilkington added a subscriber: cfe-commits.

Previously, when the 2 expressions passed to a ternary operator were xvalues and one inherits from the other, the resulting expression had type 'T', not 'T&&' as 5.16p3 dictates. For example:
`
Base b; Derived d;
typedef decltype(true ? static_cast<Base&&>(b) : static_cast<Derived&&>(d)) x; // x has type Base, not Base&&`

PR: https://llvm.org/bugs/show_bug.cgi?id=26448

http://reviews.llvm.org/D17451

Files:
  lib/Sema/SemaExprCXX.cpp
  test/SemaCXX/conditional-expr.cpp

Index: test/SemaCXX/conditional-expr.cpp
===================================================================
--- test/SemaCXX/conditional-expr.cpp
+++ test/SemaCXX/conditional-expr.cpp
@@ -384,3 +384,12 @@
     int &test() { return b_ ? i_ : throw 1; }
   };
 }
+
+namespace PR26448 {
+struct Base {};
+struct Derived : Base {};
+Base b;
+Derived d;
+typedef decltype(true ? static_cast<Base&&>(b) : static_cast<Derived&&>(d)) x;
+typedef Base &&x;
+}
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -4671,7 +4671,7 @@
   return Result;
 }
 
-/// \brief Try to convert a type to another according to C++0x 5.16p3.
+/// \brief Try to convert a type to another according to C++11 5.16p3.
 ///
 /// This is part of the parameter validation for the ? operator. If either
 /// value operand is a class type, the two operands are attempted to be
@@ -4687,17 +4687,21 @@
 
   InitializationKind Kind = InitializationKind::CreateCopy(To->getLocStart(),
                                                            SourceLocation());
-  // C++0x 5.16p3
+  // C++11 5.16p3
   //   The process for determining whether an operand expression E1 of type T1
   //   can be converted to match an operand expression E2 of type T2 is defined
   //   as follows:
-  //   -- If E2 is an lvalue:
-  bool ToIsLvalue = To->isLValue();
-  if (ToIsLvalue) {
-    //   E1 can be converted to match E2 if E1 can be implicitly converted to
-    //   type "lvalue reference to T2", subject to the constraint that in the
-    //   conversion the reference must bind directly to E1.
-    QualType T = Self.Context.getLValueReferenceType(ToType);
+  //   -- If E2 is an lvalue: E1 can be converted to match E2 if E1 can be
+  //      implicitly converted to type "lvalue reference to T2", subject to the
+  //      constraint that in the conversion the reference must bind directly to
+  //      E1.
+  //   -- If E2 is an xvalue: E1 can be converted to match E2 if E1 can be
+  //      implicitly conveted to the type "rvalue reference to R2", subject to
+  //      the constraint that the reference must bind directly.
+  if (To->isLValue() || To->isXValue()) {
+    QualType T = To->isLValue() ? Self.Context.getLValueReferenceType(ToType)
+                                : Self.Context.getRValueReferenceType(ToType);
+
     InitializedEntity Entity = InitializedEntity::InitializeTemporary(T);
 
     InitializationSequence InitSeq(Self, Entity, Kind, From);


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