From: Eric Botcazou <ebotca...@adacore.com>
The initial implementation of the GNAT aspect/pragma Volatile_Full_Access
made it incompatible with Atomic, because it was not decided whether the
read-modify-write sequences generated by Volatile_Full_Access would need
to be implemented atomically when Atomic was also specified, which would
have required a compare-and-swap primitive from the target architecture.
But Ada 2022 introduced Full_Access_Only and retrofitted it into Atomic
in the process, answering the above question by the negative, so the
incompatibility between Volatile_Full_Access and Atomic was lifted in
Ada 2012 as well, unfortunately without adjusting the implementation.
gcc/ada/
* gcc-interface/trans.cc (get_atomic_access): Deal specifically with
nodes that are both Atomic and Volatile_Full_Access in Ada 2012.
Tested on x86_64-pc-linux-gnu, committed on master.
---
gcc/ada/gcc-interface/trans.cc | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/gcc/ada/gcc-interface/trans.cc b/gcc/ada/gcc-interface/trans.cc
index 7cced04361d..caa0f56a34d 100644
--- a/gcc/ada/gcc-interface/trans.cc
+++ b/gcc/ada/gcc-interface/trans.cc
@@ -4387,9 +4387,9 @@ get_atomic_access (Node_Id gnat_node, atomic_acces_t
*type, bool *sync)
gnat_node = Expression (gnat_node);
/* Up to Ada 2012, for Atomic itself, only reads and updates of the object as
- a whole require atomic access (RM C.6(15)). But, starting with Ada 2022,
- reads of or writes to a nonatomic subcomponent of the object also require
- atomic access (RM C.6(19)). */
+ a whole require atomic access (RM C.6(15)), unless the object is also VFA.
+ But, starting with Ada 2022, reads of or writes to nonatomic subcomponents
+ of the object also require atomic access (RM C.6(19)). */
if (node_is_atomic (gnat_node))
{
bool as_a_whole = true;
@@ -4398,7 +4398,9 @@ get_atomic_access (Node_Id gnat_node, atomic_acces_t
*type, bool *sync)
for (gnat_temp = gnat_node, gnat_parent = Parent (gnat_temp);
node_is_component (gnat_parent) && Prefix (gnat_parent) == gnat_temp;
gnat_temp = gnat_parent, gnat_parent = Parent (gnat_temp))
- if (Ada_Version < Ada_2022 || node_is_atomic (gnat_parent))
+ if (Ada_Version < Ada_2022
+ ? !node_is_volatile_full_access (gnat_node)
+ : node_is_atomic (gnat_parent))
goto not_atomic;
else
as_a_whole = false;
--
2.45.2
