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.

gcc/cp/ChangeLog

+2020-02-05  Jun Ma <JunMa@linux.alibaba.com>
+
+	* 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.
+
 2020-02-04  Jason Merrill  <jason@redhat.com>
 
 	PR c++/93551

gcc/cp/coroutines.cc

@@ -803,9 +803,12 @@ build_co_await (location_t loc, tree a, suspend_point_kind suspend_kind)
   TREE_VEC_ELT (awaiter_calls, 1) = awsp_call; /* await_suspend().  */
   TREE_VEC_ELT (awaiter_calls, 2) = awrs_call; /* await_resume().  */
 
-  return build5_loc (loc, CO_AWAIT_EXPR, TREE_TYPE (awrs_call), a,
-		     e_proxy, o, awaiter_calls,
-		     build_int_cst (integer_type_node, (int) suspend_kind));
+  tree await_expr = build5_loc (loc, CO_AWAIT_EXPR,
+				TREE_TYPE (TREE_TYPE (awrs_func)),
+				a, e_proxy, o, awaiter_calls,
+				build_int_cst (integer_type_node,
+					       (int) suspend_kind));
+  return convert_from_reference (await_expr);
 }
 
 tree
@@ -1566,6 +1569,9 @@ co_await_expander (tree *stmt, int * /*do_subtree*/, void *d)
   /* This will produce the value (if one is provided) from the co_await
      expression.  */
   tree resume_call = TREE_VEC_ELT (awaiter_calls, 2); /* await_resume().  */
+  if (REFERENCE_REF_P (resume_call))
+    /* Sink to await_resume call_expr.  */
+    resume_call = TREE_OPERAND (resume_call, 0);
   switch (stmt_code)
     {
     default: /* not likely to work .. but... */

gcc/testsuite/ChangeLog

+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

gcc/testsuite/g++.dg/coroutines/torture/co-await-14-return-ref-to-auto.C

+//  { 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;
+}