Re: [PATCH] c++,coroutines: Stabilize names of promoted slot vars [PR101118].

[Jason Merrill <jason@redhat.com>]

On 3/30/23 03:53, Iain Sandoe wrote:
> Hi Jason,
> 
>> On 30 Mar 2023, at 00:53, Jason Merrill <jason@redhat.com> wrote:
>>
>> On 3/26/23 12:54, Iain Sandoe wrote:
>>> Tested on x86_64-darwin21, x86-64-linux-gnu
> 
>>>   +/* This is used to make a stable, but unique-per-function, sequence number for
>>> +   each TARGET_EXPR slot variable that we 'promote' to a frame entry.  It needs
>>> +   to be stable because the frame type is visible to LTO ODR checking.  */
>>> +static unsigned tmpno = 0;
>>
>> How about using temps_used->elements() for the index instead of a separate static counter?
> 
> That’s a good idea (the only slightly weird effect is that the count does not start at 0,
> because we’ve added one or more entries by the time we get to produce a name, but
> that does not affect functionality).

Perhaps promoted->elements() would be a better choice?  OK either way.

> re-tested on x86_64-darwin21, as below,
> OK for trunk?
> thanks
> Iain
> 
> ===
> 
> [PATCH] c++,coroutines: Stabilize names of promoted slot vars  [PR101118].
> 
> When we need to 'promote' a value (i.e. store it in the coroutine frame) it
> is given a frame entry name.  This was based on the DECL_UID for slot vars.
> However, when LTO is used, the names from multiple TUs become visible at the
> same time, and the DECL_UIDs usually differ between units.  This leads to a
> "ODR mismatch" warning for the frame type.
> 
> The fix here is to use the current promoted temporaries count to produce
> the name, this is stable between TUs and computed per coroutine.
> 
> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
> 
> 	PR c++/101118
> 
> gcc/cp/ChangeLog:
> 
> 	* coroutines.cc (flatten_await_stmt): Use the current count of
> 	promoted temporaries to build a unique name for the frame entries.
> ---
>   gcc/cp/coroutines.cc | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index a2189e43db8..9f546db7437 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -2889,7 +2889,7 @@ flatten_await_stmt (var_nest_node *n, hash_set<tree> *promoted,
>   	  tree init = t;
>   	  temps_used->add (init);
>   	  tree var_type = TREE_TYPE (init);
> -	  char *buf = xasprintf ("D.%d", DECL_UID (TREE_OPERAND (init, 0)));
> +	  char *buf = xasprintf ("T%03u", temps_used->elements());
>   	  tree var = build_lang_decl (VAR_DECL, get_identifier (buf), var_type);
>   	  DECL_ARTIFICIAL (var) = true;
>   	  free (buf);
> —
> 
>