Introduce a new AST node describing reference binding to temporaries.

MaterializeTemporaryExpr captures a reference binding to a temporary
value, making explicit that the temporary value (a prvalue) needs to
be materialized into memory so that its address can be used. The
intended AST invariant here is that a reference will always bind to a
glvalue, and MaterializeTemporaryExpr will be used to convert prvalues
into glvalues for that binding to happen. For example, given

  const int& r = 1.0;

The initializer of "r" will be a MaterializeTemporaryExpr whose
subexpression is an implicit conversion from the double literal "1.0"
to an integer value. 

IR generation benefits most from this new node, since it was
previously guessing (badly) when to materialize temporaries for the
purposes of reference binding. There are likely more refactoring and
cleanups we could perform there, but the introduction of
MaterializeTemporaryExpr fixes PR9565, a case where IR generation
would effectively bind a const reference directly to a bitfield in a
struct. Addresses <rdar://problem/9552231>.




git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133521 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index 5bdadc6166..3231455f5a 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -4075,12 +4075,13 @@ InitializationSequence::Perform(Sema &S,
       break;
 
     case SK_BindReferenceToTemporary:
-      // Reference binding does not have any corresponding ASTs.
-
       // Check exception specifications
       if (S.CheckExceptionSpecCompatibility(CurInit.get(), DestType))
         return ExprError();
 
+      // Materialize the temporary into memory.
+      CurInit = new (S.Context) MaterializeTemporaryExpr(CurInit.get(),
+                                     Entity.getType()->isLValueReferenceType());
       break;
 
     case SK_ExtraneousCopyToTemporary: