GC private tables (#265)

crates/tests/tests/spec-tests.rs

@@ -148,8 +148,10 @@ fn run(wast: &Path) -> Result<(), anyhow::Error> {
         // Tests which assert that they're not linkable tend to not work with
         // the gc pass because it removes things which would cause a module to
         // become unlinkable. This doesn't matter too much in the real world
-        // (hopefully), so just don't gc assert_unlinkable modules.
-        if cmd != "assert_unlinkable" {
+        // (hopefully), so just don't gc assert_unlinkable modules. The same
+        // applies to assert_uninstantiable modules due to removal of unused
+        // elements and tables.
+        if !matches!(cmd.as_str(), "assert_unlinkable" | "assert_uninstantiable") {
             walrus::passes::gc::run(&mut module);
         }
 

src/passes/used.rs

@@ -130,9 +130,15 @@ impl Used {
         for elem in module.elements.iter() {
             match elem.kind {
                 // Active segments are rooted because they initialize imported
-                // or exported tables. Declared segments can probably get gc'd
-                // but for now we're conservative and we root them.
-                ElementKind::Active { .. } | ElementKind::Declared => {
+                // tables.
+                ElementKind::Active { table, .. } => {
+                    if module.tables.get(table).import.is_some() {
+                        stack.push_element(elem.id());
+                    }
+                }
+                // Declared segments can probably get gc'd but for now we're
+                // conservative and we root them
+                ElementKind::Declared => {
                     stack.push_element(elem.id());
                 }
                 ElementKind::Passive => {}