Support atomic struct accessors (#7155)

Implement support for both sequentially consistent and acquire-release
variants of `struct.atomic.get` and `struct.atomic.set`, as proposed by
shared-everything-threads. Introduce a new `MemoryOrdering` enum for
describing different levels of atomicity (or the lack thereof). This new
enum should eventually be adopted by linear memory atomic accessors as
well to support acquire-release semantics, but for now just use it in
`StructGet` and `StructSet`.

In addition to implementing parsing and emitting for the instructions,
validate that shared-everything is enabled to use them, mark them as
having synchronization side effects, and lightly optimize them by
relaxing acquire-release accesses to non-shared structs to normal,
unordered accesses. This is valid because such accesses cannot possibly
synchronize with other threads. Also update Precompute to avoid
optimizing out synchronization points.

There are probably other passes that need to be updated to avoid
incorrectly optimizing synchronizing accesses, but identifying and
fixing them is left as future work.

1 files changed, 4 insertions, 0 deletions

diff --git a/scripts/gen-s-parser.py b/scripts/gen-s-parser.py
index d15c07e8e..b5592d433 100755
--- a/scripts/gen-s-parser.py
+++ b/scripts/gen-s-parser.py
@@ -617,7 +617,11 @@ instructions = [
     ("struct.get",           "makeStructGet()"),
     ("struct.get_s",         "makeStructGet(true)"),
     ("struct.get_u",         "makeStructGet(false)"),
+    ("struct.atomic.get",    "makeAtomicStructGet()"),
+    ("struct.atomic.get_s",  "makeAtomicStructGet(true)"),
+    ("struct.atomic.get_u",  "makeAtomicStructGet(false)"),
     ("struct.set",           "makeStructSet()"),
+    ("struct.atomic.set",    "makeAtomicStructSet()"),
     ("array.new",            "makeArrayNew(false)"),
     ("array.new_default",    "makeArrayNew(true)"),
     ("array.new_data",       "makeArrayNewData()"),