Handle type deduction of auto and decltype(auto) with reference expression

gcc/cp
    * coroutines.cc (build_co_await): Call convert_from_reference
    to wrap co_await_expr with indirect_ref which avoid
    reference/non-reference type confusion.

    (co_await_expander):  Sink to call_expr if await_resume
    is wrapped by indirect_ref.

gcc/testsuite
    * g++.dg/coroutines/co-await-14-return-ref-to-auto.C: New test.

2 files changed, 49 insertions, 0 deletions

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d2dc664..3b2be71 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-02-05  Jun Ma <JunMa@linux.alibaba.com>
+
+	* g++.dg/coroutines/co-await-14-return-ref-to-auto.C: New test.
+
 2020-02-04  David Malcolm  <dmalcolm@redhat.com>
 
 	* gcc.dg/analyzer/data-model-1.c (struct coord): Convert fields
diff --git a/gcc/testsuite/g++.dg/coroutines/torture/co-await-14-return-ref-to-auto.C b/gcc/testsuite/g++.dg/coroutines/torture/co-await-14-return-ref-to-auto.C
new file mode 100644
index 0000000..0a7c035
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/torture/co-await-14-return-ref-to-auto.C
@@ -0,0 +1,45 @@
+//  { dg-do run }
+
+/* The simplest valued co_await we can do.  */
+
+#include "../coro.h"
+
+// boiler-plate for tests of codegen
+#include "../coro1-ret-int-yield-int.h"
+
+
+coro1
+f ()
+{
+  int t1 = 5;
+  int t2 = 5;
+  auto gX = co_await coro1::suspend_always_intrefprt{t1};
+  if (gX != t1)
+	  abort();
+  decltype(auto) gX1 = co_await coro1::suspend_always_intrefprt{t2};
+  if (&gX1 != &t2)
+	  abort();
+  co_return t1 + 10;
+}
+
+int main ()
+{
+  PRINT ("main: create coro1");
+  struct coro1 f_coro = f ();
+  if (f_coro.handle.done())
+    {
+      PRINT ("main: we should not be 'done' [1]");
+      abort ();
+    }
+  PRINT ("main: resuming [1] initial suspend");
+  while (!f_coro.handle.done())
+    f_coro.handle.resume();
+  /* we should now have returned with the co_return (15) */
+  if (!f_coro.handle.done())
+    {
+      PRINT ("main: we should be 'done' ");
+      abort ();
+    }
+  puts ("main: done");
+  return 0;
+}