DR1213: element access on an array xvalue or prvalue produces an xvalue. In the

latter case, a temporary array object is materialized, and can be
lifetime-extended by binding a reference to the member access. Likewise, in an
array-to-pointer decay, an rvalue array is materialized before being converted
into a pointer.

This caused IR generation to stop treating file-scope array compound literals
as having static storage duration in some cases in C++; that has been rectified
by modeling such a compound literal as an lvalue. This also improves clang's
compatibility with GCC for those cases.

llvm-svn: 288654

1 files changed, 12 insertions, 0 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index fd1a94e..fc76a86 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -390,6 +390,18 @@ ExprResult Sema::ImpCastExprToType(Expr *E, QualType Ty,
   if (ExprTy == TypeTy)
     return E;
 
+  // C++1z [conv.array]: The temporary materialization conversion is applied.
+  // We also use this to fuel C++ DR1213, which applies to C++11 onwards.
+  if (Kind == CK_ArrayToPointerDecay && getLangOpts().CPlusPlus &&
+      E->getValueKind() == VK_RValue) {
+    // The temporary is an lvalue in C++98 and an xvalue otherwise.
+    ExprResult Materialized = CreateMaterializeTemporaryExpr(
+        E->getType(), E, !getLangOpts().CPlusPlus11);
+    if (Materialized.isInvalid())
+      return ExprError();
+    E = Materialized.get();
+  }
+
   if (ImplicitCastExpr *ImpCast = dyn_cast<ImplicitCastExpr>(E)) {
     if (ImpCast->getCastKind() == Kind && (!BasePath || BasePath->empty())) {
       ImpCast->setType(Ty);