From 2a908f3da07c9e94b8a19e966b45daf0140107e8 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Mon, 24 Jan 2022 09:17:35 -0500
Subject: [PATCH] c++: value category of compound object expr [PR104173]

Here the call to (the &&-qualified) toLower() is incorrectly rejected
during overload resolution because the object expression is encoded as
an lvalue when it's really a prvalue.  The object expression,
instance()->applicationName(), is encoded as an INDIRECT_REF of a
COMPOUND_EXPR

  *(*instance ();, &TARGET_EXPR <D.2383, QCoreApplication::applicationName ()>;);

which lvalue_kind deems an lvalue.

This issue is similar to PR88103 except that here the original compound
object expression is a prvalue rather than an xvalue.  The fix there was to
adjust the result of unary_complex_lvalue in build_class_member_access_expr
so that xvalueness of the original expression is preserved.  This patch
extends that fix so that rvalueness is preserved more generally.

	PR c++/104173

gcc/cp/ChangeLog:

	* typeck.cc (build_class_member_access_expr): Extend
	unary_complex_lvalue result adjustment to preserve all
	rvalues, not just xvalues.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/ref-qual21.C: New test.
---
 gcc/cp/typeck.cc                        | 19 ++++++++-----------
 gcc/testsuite/g++.dg/cpp0x/ref-qual21.C | 23 +++++++++++++++++++++++
 2 files changed, 31 insertions(+), 11 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/ref-qual21.C

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 3a28d63..11c9d8a 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -2726,17 +2726,14 @@ build_class_member_access_expr (cp_expr object, tree member,
   /* Transform `(a, b).x' into `(*(a, &b)).x', `(a ? b : c).x' into
      `(*(a ?  &b : &c)).x', and so on.  A COND_EXPR is only an lvalue
      in the front end; only _DECLs and _REFs are lvalues in the back end.  */
-  {
-    tree temp = unary_complex_lvalue (ADDR_EXPR, object);
-    if (temp)
-      {
-	temp = cp_build_fold_indirect_ref (temp);
-	if (xvalue_p (object) && !xvalue_p (temp))
-	  /* Preserve xvalue kind.  */
-	  temp = move (temp);
-	object = temp;
-      }
-  }
+  if (tree temp = unary_complex_lvalue (ADDR_EXPR, object))
+    {
+      temp = cp_build_fold_indirect_ref (temp);
+      if (!lvalue_p (object) && lvalue_p (temp))
+	/* Preserve rvalueness.  */
+	temp = move (temp);
+      object = temp;
+    }
 
   /* In [expr.ref], there is an explicit list of the valid choices for
      MEMBER.  We check for each of those cases here.  */
diff --git a/gcc/testsuite/g++.dg/cpp0x/ref-qual21.C b/gcc/testsuite/g++.dg/cpp0x/ref-qual21.C
new file mode 100644
index 0000000..7f867c2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/ref-qual21.C
@@ -0,0 +1,23 @@
+// PR c++/104173
+// { dg-do compile { target c++11 } }
+
+struct QString {
+  QString toLower() &&;
+};
+
+struct QCoreApplication {
+  static QString applicationName();
+};
+
+QCoreApplication* instance();
+
+void f() {
+  instance()->applicationName().toLower();
+}
+
+template<class...>
+void g() {
+  instance()->applicationName().toLower();
+}
+
+template void g<>();
-- 
2.7.4