[PATCH][c++] Fix DECL_BY_REFERENCE of clone parms

[Tom de Vries]

Hi,

Consider test.C compiled at -O0 -g:
...
class string {
public:
  string (const char *p) { this->p = p ; }
  string (const string &s) { this->p = s.p; }

private:
  const char *p;
};

class foo {
public:
  foo (string dir_hint) {}
};

int
main (void)
{
  std::string s = "This is just a string";
  foo bar(s);
  return 0;
}
...

When parsing foo::foo, the dir_hint parameter gets a DECL_ARG_TYPE of
'struct string & restrict'.  Then during finish_struct, we call
clone_constructors_and_destructors and create clones for foo::foo, and
set the DECL_ARG_TYPE in the same way.

Later on, during finish_function, cp_genericize is called for the original
foo::foo, which sets the type of parm dir_hint to DECL_ARG_TYPE, and sets
DECL_BY_REFERENCE of dir_hint to 1.

After that, during maybe_clone_body update_cloned_parm is called with:
...
(gdb) call debug_generic_expr (parm.typed.type)
struct string & restrict
(gdb) call debug_generic_expr (cloned_parm.typed.type)
struct string
...
The type of the cloned_parm is then set to the type of parm, but
DECL_BY_REFERENCE is not set.

When doing cp_genericize for the clone later on,
TREE_ADDRESSABLE (TREE_TYPE ()) is no longer true for the updated type of
the parm, so DECL_BY_REFERENCE is not set there either.

This patch fixes the problem by copying DECL_BY_REFERENCE in update_cloned_parm.

Build and reg-tested on x86_64.

OK for trunk?

Thanks,
- Tom

[c++] Fix DECL_BY_REFERENCE of clone parms

2018-07-30  Tom de Vries  <tdevr...@suse.de>

        PR debug/86687
        * optimize.c (update_cloned_parm): Copy DECL_BY_REFERENCE.

        * g++.dg/guality/pr86687.C: New test.

---
 gcc/cp/optimize.c                      |  2 ++
 gcc/testsuite/g++.dg/guality/pr86687.C | 28 ++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/gcc/cp/optimize.c b/gcc/cp/optimize.c
index 0e9b84ed8a4..3923a5fc6c4 100644
--- a/gcc/cp/optimize.c
+++ b/gcc/cp/optimize.c
@@ -46,6 +46,8 @@ update_cloned_parm (tree parm, tree cloned_parm, bool first)
   /* We may have taken its address.  */
   TREE_ADDRESSABLE (cloned_parm) = TREE_ADDRESSABLE (parm);
 
+  DECL_BY_REFERENCE (cloned_parm) = DECL_BY_REFERENCE (parm);
+
   /* The definition might have different constness.  */
   TREE_READONLY (cloned_parm) = TREE_READONLY (parm);
 
diff --git a/gcc/testsuite/g++.dg/guality/pr86687.C 
b/gcc/testsuite/g++.dg/guality/pr86687.C
new file mode 100644
index 00000000000..140a6fce596
--- /dev/null
+++ b/gcc/testsuite/g++.dg/guality/pr86687.C
@@ -0,0 +1,28 @@
+// PR debug/86687
+// { dg-do run }
+// { dg-options "-g" }
+
+class string {
+public:
+  string (int p) { this->p = p ; }
+  string (const string &s) { this->p = s.p; }
+
+  int p;
+};
+
+class foo {
+public:
+  foo (string dir_hint) {
+    p = dir_hint.p; // { dg-final { gdb-test . "dir_hint.p" 3 } }
+  }
+
+  int p;
+};
+
+int
+main (void)
+{
+  string s = 3;
+  foo bar(s);
+  return !(bar.p == 3);
+}