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c++, coroutines: Make suspend index consistent for debug.

Message ID 20241129134721.52008-1-iain@sandoe.co.uk
State New
Headers
Series c++, coroutines: Make suspend index consistent for debug. |

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Commit Message

Iain Sandoe Nov. 29, 2024, 1:47 p.m. UTC 
  Tested on x86_64-darwin, x86_64-linux,
OK for trunk?
thanks
Iain

--- 8< ---

At present, we only update the suspend index when we actually are
at the stage that the coroutine is considered suspended. This is
on the basis that it is UB to resume or destroy a coroutines that
is not suspended (and therefore we never need to access this value
otherwise).  However, it is possible that someone could set a debug
breakpoint on the resume which can be reached without suspending
if await_ready() returns true.  In that case, the debugger would
read an incorrect suspend index.  Fixed by moving the update to
just before the test for ready.

gcc/cp/ChangeLog:

	* coroutines.cc (expand_one_await_expression): Update the
	suspend point index before checking if the coroutine is
	ready.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
---
 gcc/cp/coroutines.cc | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
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Patch

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 3148559d208..b36730d793c 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -1964,6 +1964,11 @@  expand_one_await_expression (tree *expr, tree *await_expr, void *d)
 
   /* Use the await_ready() call to test if we need to suspend.  */
   tree ready_cond = TREE_VEC_ELT (awaiter_calls, 0); /* await_ready().  */
+  /* We are about to pass this suspend point.  */
+  tree susp_idx = build_int_cst (short_unsigned_type_node, data->index);
+  tree r = cp_build_init_expr (data->resume_idx, susp_idx);
+  finish_expr_stmt (r);
+
   /* Convert to bool, if necessary.  */
   if (TREE_CODE (TREE_TYPE (ready_cond)) != BOOLEAN_TYPE)
     ready_cond = cp_convert (boolean_type_node, ready_cond,
@@ -1974,10 +1979,6 @@  expand_one_await_expression (tree *expr, tree *await_expr, void *d)
   ready_cond = invert_truthvalue_loc (loc, ready_cond);
   finish_if_stmt_cond (ready_cond, susp_if);
 
-  tree susp_idx = build_int_cst (short_unsigned_type_node, data->index);
-  tree r = cp_build_init_expr (data->resume_idx, susp_idx);
-  finish_expr_stmt (r);
-
   /* Find out what we have to do with the awaiter's suspend method.
      [expr.await]
      (5.1) If the result of await-ready is false, the coroutine is considered