c++: Fix coroutines on targetm.cxx.cdtor_return_this targets [PR99459]

The r11-7528 build_co_await changes broke coroutines on arm*-linux-gnuabi,
2780 ^FAIL.*coroutines/ in total.
The problem is that arm is targetm.cxx.cdtor_return_this target where
both ctors and dtors in the ABI return this pointer rather than
void, and build_new_method_call_1 does:
              else if (call != error_mark_node
                       && DECL_DESTRUCTOR_P (cand->fn)
                       && !VOID_TYPE_P (TREE_TYPE (call)))
                /* An explicit call of the form "x->~X()" has type
                   "void".  However, on platforms where destructors
                   return "this" (i.e., those where
                   targetm.cxx.cdtor_returns_this is true), such calls
                   will appear to have a return value of pointer type
                   to the low-level call machinery.  We do not want to
                   change the low-level machinery, since we want to be
                   able to optimize "delete f()" on such platforms as
                   "operator delete(~X(f()))" (rather than generating
                   "t = f(), ~X(t), operator delete (t)").  */
                call = build_nop (void_type_node, call);
The new code in build_co_await relies on build_special_member_call
returned expression being a CALL_EXPR, but due to the build_nop
in there it is a NOP_EXPR around the CALL_EXPR.  It can't be stripped
with STRIP_NOPS because void has different mode from the pointer mode.

2021-03-09  Jakub Jelinek  <jakub@redhat.com>

	PR c++/99459
	* coroutines.cc (build_co_await): Look through NOP_EXPRs in
	build_special_member_call return value to find the CALL_EXPR.
	Simplify.

1 files changed, 18 insertions, 16 deletions

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 897c1a0..c5aeb66 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -863,16 +863,17 @@ build_co_await (location_t loc, tree a, suspend_point_kind suspend_kind)
 	     final awaiter, so check for a non-throwing DTOR where needed.  */
 	  tree a_type = TREE_TYPE (a);
 	  if (TYPE_HAS_NONTRIVIAL_DESTRUCTOR (a_type))
-	    {
-	      tree dummy
+	    if (tree dummy
 		= build_special_member_call (a, complete_dtor_identifier,
 					     NULL, a_type, LOOKUP_NORMAL,
-					     tf_none);
-	      dummy = dummy ? TREE_OPERAND (CALL_EXPR_FN (dummy), 0)
-			    : NULL_TREE;
-	      if (dummy && coro_diagnose_throwing_fn (dummy))
-		return error_mark_node;
-	    }
+					     tf_none))
+	      {
+		if (CONVERT_EXPR_P (dummy))
+		  dummy = TREE_OPERAND (dummy, 0);
+		dummy = TREE_OPERAND (CALL_EXPR_FN (dummy), 0);
+		if (coro_diagnose_throwing_fn (dummy))
+		  return error_mark_node;
+	      }
 	}
     }
   else
@@ -1026,16 +1027,17 @@ build_co_await (location_t loc, tree a, suspend_point_kind suspend_kind)
       if (coro_diagnose_throwing_fn (awrs_func))
 	return error_mark_node;
       if (TYPE_HAS_NONTRIVIAL_DESTRUCTOR (o_type))
-	{
-	  tree dummy
+	if (tree dummy
 	    = build_special_member_call (e_proxy, complete_dtor_identifier,
 					 NULL, o_type, LOOKUP_NORMAL,
-					 tf_none);
-	  dummy = dummy ? TREE_OPERAND (CALL_EXPR_FN (dummy), 0)
-			: NULL_TREE;
-	  if (dummy && coro_diagnose_throwing_fn (dummy))
-	    return error_mark_node;
-	}
+					 tf_none))
+	  {
+	    if (CONVERT_EXPR_P (dummy))
+	      dummy = TREE_OPERAND (dummy, 0);
+	    dummy = TREE_OPERAND (CALL_EXPR_FN (dummy), 0);
+	    if (coro_diagnose_throwing_fn (dummy))
+	      return error_mark_node;
+	  }
     }
 
   /* We now have three call expressions, in terms of the promise, handle and