[gcc r12-9502] c++, coroutines: Fix block nests when the function has no top-level bind.

[Iain D Sandoe <iains@gcc.gnu.org>]

https://gcc.gnu.org/g:66e43c2387402f1fd48c71fe10275fa8f4c427d5

commit r12-9502-g66e43c2387402f1fd48c71fe10275fa8f4c427d5
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sat Apr 1 21:53:51 2023 +0530

    c++, coroutines: Fix block nests when the function has no top-level bind.
    
    When the function contains no local vars and also no nested scopes, there
    is no top-level bind expression.  Because the rewritten coroutine body will
    require both local vars and contain nested scopes, we add a bind expression
    to such functions.  When this was done the necessary scope blocks were
    omitted which leads to disconnected function content.
    
    Fixed by adding a new block to the added bind expression.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
    gcc/cp/ChangeLog:
    
            * coroutines.cc (coro_rewrite_function_body): Ensure that added
            bind expressions have scope blocks.
    
    (cherry picked from commit a8d7631d333c22e38a067d32d11fd2b60cf1d960)

Diff:
---
 gcc/cp/coroutines.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 03ba3f6aa26..85a760d8220 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -4109,6 +4109,10 @@ coro_rewrite_function_body (location_t fn_start, tree fnbody, tree orig,
       tree bind_wrap = build3_loc (fn_start, BIND_EXPR, void_type_node,
 				   NULL, NULL, NULL);
       BIND_EXPR_BODY (bind_wrap) = fnbody;
+      /* Ensure we have a block to connect up the scopes.  */
+      tree new_blk = make_node (BLOCK);
+      BIND_EXPR_BLOCK (bind_wrap) = new_blk;
+      BLOCK_SUBBLOCKS (top_block) = new_blk;
       fnbody = bind_wrap;
     }