On Sun, Mar 26, 2023 at 6:55 PM Iain Sandoe via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Tested on x86_64-darwin21, x86-64-linux-gnu
> OK for trunk?
> Iain
>
> 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 a counter instead of the DECL_UID which makes a name
> that is stable between TUs for each frame layout (one per coroutine func).
I don't see how this avoids clashes across TUs? But are those VAR_DECLs not
local anyway?
I suppose -Wodr diagnostics for DECL_ARTIFICIAL vars are a bit on the
edge as well ...
Richard.
> Signed-off-by: Iain Sandoe <i...@sandoe.co.uk>
>
> PR c++/101118
>
> gcc/cp/ChangeLog:
>
> * coroutines.cc: Add counter for promoted slot vars.
> (flatten_await_stmt): Use slot vars counter instead of DECL_UID
> to generate the frame entry name for promoted target expression
> slot variables.
> (morph_fn_to_coro): Reset the slot vars counter at the start of
> each coroutine function.
> ---
> gcc/cp/coroutines.cc | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index a2189e43db8..359a5bf46ff 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -2726,6 +2726,11 @@ struct var_nest_node
> var_nest_node *else_cl;
> };
>
> +/* 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;
> +
> /* This is called for single statements from the co-await statement walker.
> It checks to see if the statement contains any initializers for awaitables
> and if any of these capture items by reference. */
> @@ -2889,7 +2894,7 @@ 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", tmpno++);
> tree var = build_lang_decl (VAR_DECL, get_identifier (buf),
> var_type);
> DECL_ARTIFICIAL (var) = true;
> free (buf);
> @@ -4374,6 +4379,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree
> *destroyer)
> {
> gcc_checking_assert (orig && TREE_CODE (orig) == FUNCTION_DECL);
>
> + tmpno = 0;
> *resumer = error_mark_node;
> *destroyer = error_mark_node;
> if (!coro_function_valid_p (orig))
> --
> 2.37.1 (Apple Git-137.1)
>
