c++: fix missing lifetime extension [PR119383]

Since r15-8011 cp_build_indirect_ref_1 won't do the *&TARGET_EXPR ->
TARGET_EXPR folding not to change its value category.  That fix seems
correct but it made us stop extending the lifetime in this testcase,
causing a wrong-code issue -- extend_ref_init_temps_1 did not see
through the extra *& because it doesn't use a tree walk.

This patch reverts r15-8011 and instead handles the problem in
build_over_call by calling force_lvalue in the is_really_empty_class
case as well as in the general case.

	PR c++/119383

gcc/cp/ChangeLog:

	* call.cc (build_over_call): Use force_lvalue to ensure op= returns
	an lvalue.
	* cp-tree.h (force_lvalue): Declare.
	* cvt.cc (force_lvalue): New.
	* typeck.cc (cp_build_indirect_ref_1): Revert r15-8011.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/temp-extend3.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/cpp0x/temp-extend3.C b/gcc/testsuite/g++.dg/cpp0x/temp-extend3.C
new file mode 100644
index 0000000..3eab88d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/temp-extend3.C
@@ -0,0 +1,32 @@
+// PR c++/119383
+// { dg-do run { target c++11 } }
+
+int g;
+
+struct base {
+  virtual base *clone() const = 0;
+  ~base() { }
+};
+
+struct impl : virtual base {
+  base *clone() const { return new impl; }  // #1
+  impl() { ++g; }
+  ~impl() { --g; }
+};
+
+const base *
+make_a_clone ()
+{
+  const base &base = impl{}; // #2
+  return base.clone();
+}
+
+int
+main ()
+{
+  make_a_clone ();
+  // impl::impl() is called twice (#1 and #2), impl::~impl() once,
+  // at the end of make_a_clone.
+  if (g != 1)
+    __builtin_abort ();
+}