Account for weak memory in the tag GC (crudely)

Author: saethlin

src/concurrency/range_object_map.rs

@@ -132,6 +132,10 @@ impl<T> RangeObjectMap<T> {
     pub fn remove_from_pos(&mut self, pos: Position) {
         self.v.remove(pos);
     }
+
+    pub fn iter(&self) -> impl Iterator<Item = &T> {
+        self.v.iter().map(|e| &e.data)
+    }
 }
 
 impl<T> Index<Position> for RangeObjectMap<T> {

src/concurrency/weak_memory.rs

@@ -108,6 +108,19 @@ pub struct StoreBufferAlloc {
     store_buffers: RefCell<RangeObjectMap<StoreBuffer>>,
 }
 
+impl StoreBufferAlloc {
+    pub fn iter(&self, mut visitor: impl FnMut(&Scalar<Provenance>)) {
+        for val in self
+            .store_buffers
+            .borrow()
+            .iter()
+            .flat_map(|buf| buf.buffer.iter().map(|element| &element.val))
+        {
+            visitor(val)
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub(super) struct StoreBuffer {
     // Stores to this location in modification order

src/machine.rs

@@ -601,7 +601,7 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
 
 impl VisitMachineValues for MiriMachine<'_, '_> {
     fn visit_machine_values(&self, visit: &mut impl FnMut(&Operand<Provenance>)) {
-        // FIXME: visit the missing fields: weak mem, DirHandler, Stacked Borrows base pointers(?); maybe more.
+        // FIXME: visit the missing fields: DirHandler, Stacked Borrows base pointers(?); maybe more.
         let MiriMachine { threads, tls, env_vars, argc, argv, cmd_line, extern_statics, .. } = self;
 
         threads.visit_machine_values(visit);

src/tag_gc.rs

@@ -77,6 +77,16 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: MiriInterpCxExt<'mir, 'tcx> {
                     .as_ref()
                     .expect("we should not even enter the GC if Stacked Borrows is disabled");
                 tags.extend(&stacks.borrow().exposed_tags);
+
+                if let Some(store_buffers) = alloc.extra.weak_memory.as_ref() {
+                    store_buffers.iter(|val| {
+                        if let Scalar::Ptr(ptr, _) = val {
+                            if let Provenance::Concrete { sb, .. } = ptr.provenance {
+                                tags.insert(sb);
+                            }
+                        }
+                    });
+                }
             },
         );