Re: [PATCH] coroutines: Handle lambda closure pointers like 'this'.

[Nathan Sidwell]

On 5/22/20 8:27 AM, Iain Sandoe wrote:
Hi,
We didn’t quite have time to push this through before the 10.1
deadline, but (since it’s a correctness issue) it should be applied
to the branch too.

tested on x86_64-darwin, linux
OK for master?
10.2 after some bake time?
thanks
Iain

=======

It was agreed amongst the implementors that the correct
interpretation of the standard is that lambda closure pointers
should be treated in the same manner as class object pointers.

gcc/cp/ChangeLog:

        * coroutines.cc (instantiate_coro_traits): Pass a reference
        to lambda closure objects to traits instantiation.
        (morph_fn_to_coro): Likewise for promise parameter
        preview and allocator lookup.
---
  gcc/cp/coroutines.cc | 19 +++++--------------
  1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index b79e2c66b70..6e3f03bdb0d 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -304,8 +304,8 @@ instantiate_coro_traits (tree fndecl, location_t kw)
  
    while (arg_node != NULL_TREE && !VOID_TYPE_P (TREE_VALUE (arg_node)))
      {
-      /* See PR94807, as to why we must exclude lambda here.  */
-      if (is_this_parameter (arg) && !lambda_p)
+      if (is_this_parameter (arg)
+         || (lambda_p && DECL_NAME (arg) == closure_identifier))

DECL_NAME (arg) == closure_identifier is sufficient -- it's in the 
implementor's namespace.  Just like how is_this_parameter works. (that I 
fixed trunk to not label a lambda's instantiation a this pointer doesn't 
matter here, so you don't have to account for it not being so on 10.2).

        {
          /* We pass a reference to *this to the param preview.  */
          tree ct = TREE_TYPE (TREE_TYPE (arg));
@@ -3793,13 +3793,8 @@ morph_fn_to_coro (tree orig, tree *resumer, tree 
*destroyer)
            parm.frame_type = actual_type;
  
  	  parm.this_ptr = is_this_parameter (arg);
-         /* See PR94807.  When a lambda is in a template instantiation, the
-            closure object is named 'this' instead of '__closure'.  */
          if (lambda_p)
-           {
-             parm.lambda_cobj = DECL_NAME (arg) == closure_identifier;
-             gcc_checking_assert (!parm.this_ptr);
-           }
+           parm.lambda_cobj = DECL_NAME (arg) == closure_identifier;

but this bit will be different on 10.2.  I think you want
if (lambda_p)
 { parm.lambda_cobj = parm.this_ptr || DECL_NAME (arg) == 
closure_identifier;
   parm.this_pointer = false;
}
?


looks ok otherwise, for both.


--
Nathan Sidwell