[gcc r10-10723] c++: assignment to temporary [PR59950]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:080e737a851d57697d0aac55749296c5c454c421

commit r10-10723-g080e737a851d57697d0aac55749296c5c454c421
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jan 24 00:01:40 2022 -0500

    c++: assignment to temporary [PR59950]
    
    Given build_this of a TARGET_EXPR, cp_build_fold_indirect_ref returns the
    TARGET_EXPR.  But that's the wrong value category for the result of the
    defaulted class assignment operator, which returns an lvalue, so we need to
    actually build the INDIRECT_REF.
    
            PR c++/59950
    
    gcc/cp/ChangeLog:
    
            * call.c (build_over_call): Use cp_build_indirect_ref.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/init/assign2.C: New test.

Diff:
---
 gcc/cp/call.c                       | 7 +++++--
 gcc/testsuite/g++.dg/init/assign2.C | 6 ++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 49eb673ebcc..5a4f93527bd 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -9081,8 +9081,11 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	   && DECL_OVERLOADED_OPERATOR_IS (fn, NOP_EXPR)
 	   && trivial_fn_p (fn))
     {
-      tree to = cp_stabilize_reference
-	(cp_build_fold_indirect_ref (argarray[0]));
+      /* Don't use cp_build_fold_indirect_ref, op= returns an lvalue even if
+	 the object argument isn't one.  */
+      tree to = cp_build_indirect_ref (input_location, argarray[0],
+				       RO_ARROW, complain);
+      to = cp_stabilize_reference (to);
       tree type = TREE_TYPE (to);
       tree as_base = CLASSTYPE_AS_BASE (type);
       tree arg = argarray[1];
diff --git a/gcc/testsuite/g++.dg/init/assign2.C b/gcc/testsuite/g++.dg/init/assign2.C
new file mode 100644
index 00000000000..72d1264f3c9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/assign2.C
@@ -0,0 +1,6 @@
+// PR c++/59950
+
+ struct Foo {};
+
+ int f(Foo *p);
+ int n = f(&(Foo() = Foo()));