[PATCH RFC] Fix ICE due to shared BLOCK node in coroutine generation [PR103328]

[Benno Evers <benno.martin.evers@googlemail.com>]

The coroutine transformation moves the original function body into a
newly created actor function, but the block of the
`current_binding_level` still points into the original function,
causing the block to be shared between the two functions if it is
subsequently used. This may cause havoc later on, as subsequent
compiler passes for one function will also implicitly modify the
other. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103328#c19 for
a more detailed writeup.

This patch fixes the issue locally, but I'm not familiar with the GCC
code base so I'm not sure if this is the right way to go about it or
if there's a cleaner way to reset the current binding level. If this
is the way to go I'm happy to extend the patch with a testcase and
changelog entry.

---
 gcc/cp/coroutines.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index b1bfdc767a4..eb5f80f499b 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -4541,6 +4541,8 @@ morph_fn_to_coro (tree orig, tree *resumer, tree
*destroyer)
   BLOCK_VARS (top_block) = BIND_EXPR_VARS (ramp_bind);
   BLOCK_SUBBLOCKS (top_block) = NULL_TREE;

+  current_binding_level->blocks = top_block;
+
   /* The decl_expr for the coro frame pointer, initialize to zero so that we
      can pass it to the IFN_CO_FRAME (since there's no way to pass a type,
      directly apparently).  This avoids a "used uninitialized" warning.  */
-- 
2.32.0