C++ PATCH for c++/81420, lifetime extension and array subscripting

[Jason Merrill]

The first hunk fixes looking through the array reference; the second
fixes looking through the base class conversion.  There's more to do
to implement DR 1299, but this is a solid improvement from a fairly
trivial patch.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit a065c041556f30a685e2d6b02c0486f7e7e77443
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue May 1 20:23:18 2018 -0400

            PR c++/81420 - not extending temporary lifetime.
    
            * call.c (extend_ref_init_temps_1): Handle ARRAY_REF.
            * class.c (build_base_path): Avoid redundant move of an rvalue.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 1df4d14dfe6..c100a92f2fb 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -11061,7 +11061,9 @@ extend_ref_init_temps_1 (tree decl, tree init, vec<tree, va_gc> **cleanups)
   if (TREE_CODE (sub) != ADDR_EXPR)
     return init;
   /* Deal with binding to a subobject.  */
-  for (p = &TREE_OPERAND (sub, 0); TREE_CODE (*p) == COMPONENT_REF; )
+  for (p = &TREE_OPERAND (sub, 0);
+       (TREE_CODE (*p) == COMPONENT_REF
+	|| TREE_CODE (*p) == ARRAY_REF); )
     p = &TREE_OPERAND (*p, 0);
   if (TREE_CODE (*p) == TARGET_EXPR)
     {
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index a9a0fa92727..25753d4c45f 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -426,7 +426,7 @@ build_base_path (enum tree_code code,
     {
       expr = cp_build_fold_indirect_ref (expr);
       expr = build_simple_base_path (expr, binfo);
-      if (rvalue)
+      if (rvalue && lvalue_p (expr))
 	expr = move (expr);
       if (want_pointer)
 	expr = build_address (expr);
diff --git a/gcc/testsuite/g++.dg/cpp0x/temp-extend1.C b/gcc/testsuite/g++.dg/cpp0x/temp-extend1.C
new file mode 100644
index 00000000000..639f9456573
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/temp-extend1.C
@@ -0,0 +1,19 @@
+// PR c++/81420
+// { dg-do run { target c++11 } }
+
+int d;
+
+struct A
+{
+  int i[2];
+  ~A() { ++d; };
+};
+
+struct B: A {};
+
+int main()
+{
+  const int &r = B().i[0];
+  if (d != 0)
+    __builtin_abort();
+}