Add two new AST nodes to represent initialization of an array in terms of
initialization of each array element:

 * ArrayInitLoopExpr is a prvalue of array type with two subexpressions:
   a common expression (an OpaqueValueExpr) that represents the up-front
   computation of the source of the initialization, and a subexpression
   representing a per-element initializer
 * ArrayInitIndexExpr is a prvalue of type size_t representing the current
   position in the loop

This will be used to replace the creation of explicit index variables in lambda
capture of arrays and copy/move construction of classes with array elements,
and also C++17 structured bindings of arrays by value (which inexplicably allow
copying an array by value, unlike all of C++'s other array declarations).

No uses of these nodes are introduced by this change, however.

llvm-svn: 289413
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 2b54370..c15e580 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -311,6 +311,12 @@
 
   Value *VisitInitListExpr(InitListExpr *E);
 
+  Value *VisitArrayInitIndexExpr(ArrayInitIndexExpr *E) {
+    assert(CGF.getArrayInitIndex() &&
+           "ArrayInitIndexExpr not inside an ArrayInitLoopExpr?");
+    return CGF.getArrayInitIndex();
+  }
+
   Value *VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
     return EmitNullValue(E->getType());
   }