[PATCH] c++: Clear TARGET_EXPR_ELIDING_P when forced to use a copy constructor due to __no_unique_address__ [PR118199]

[Simon Martin]

We currently fail with a checking assert upon the following valid code
when using -fno-elide-constructors

=== cut here ===
struct d { ~d(); };
d &b();
struct f {
  [[__no_unique_address__]] d e;
};
struct h : f  {
  h() : f{b()} {}
} i;
=== cut here ===

The problem is that split_nonconstant_init_1 detects that it cannot
elide the copy constructor due to __no_unique_address__ but does not
clear TARGET_EXPR_ELIDING_P, and due to -fno-elide-constructors, we trip
on a checking assert in cp_gimplify_expr.

This patch fixes this by making sure that we clear TARGET_EXPR_ELIDING_P
if we determine that we have to keep the copy constructor due to
__no_unique_address__. An alternative would be to just check for
elide_constructors in that assert, but I think it'd lose most of its
value if we did so.

Successfully tested on x86_64-pc-linux-gnu.

        PR c++/118199

gcc/cp/ChangeLog:

        * typeck2.cc (split_nonconstant_init_1): Clear
        TARGET_EXPR_ELIDING_P if we need to use a copy constructor
        because of __no_unique_address__.

gcc/testsuite/ChangeLog:

        * g++.dg/init/no-elide3.C: New test.

---
 gcc/cp/typeck2.cc                     |  5 +++++
 gcc/testsuite/g++.dg/init/no-elide3.C | 12 ++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/init/no-elide3.C

diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 381f198d0fe..f50c5f767bb 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -655,6 +655,11 @@ split_nonconstant_init_1 (tree dest, tree init, bool last,
                          && make_safe_copy_elision (sub, value))
                        goto build_init;
 
+                     if (TREE_CODE (value) == TARGET_EXPR)
+                       /* We have to add this constructor, so we will not
+                          elide.  */
+                       TARGET_EXPR_ELIDING_P (value) = false;
+
                      tree name = (DECL_FIELD_IS_BASE (field_index)
                                   ? base_ctor_identifier
                                   : complete_ctor_identifier);
diff --git a/gcc/testsuite/g++.dg/init/no-elide3.C 
b/gcc/testsuite/g++.dg/init/no-elide3.C
new file mode 100644
index 00000000000..659eb19bc95
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/no-elide3.C
@@ -0,0 +1,12 @@
+// PR c++/118199
+// { dg-do "compile" { target c++11 } }
+// { dg-options "-fno-elide-constructors" } 
+
+struct d { ~d(); };
+d &b();
+struct f {
+  [[__no_unique_address__]] d e;
+};
+struct h : f  {
+  h() : f{b()} {}
+} i;
-- 
2.44.0