Implement cross-instance indirect calls.

lib/runtime/src/sig_registry.rs

@@ -3,53 +3,36 @@
 
 use cast;
 use cranelift_codegen::ir;
-use cranelift_entity::PrimaryMap;
-use cranelift_wasm::SignatureIndex;
 use std::collections::{hash_map, HashMap};
 use vmcontext::VMSharedSignatureIndex;
 
+/// WebAssembly requires that the caller and callee signatures in an indirect
+/// call must match. To implement this efficiently, keep a registry of all
+/// signatures, shared by all instances, so that call sites can just do an
+/// index comparison.
 #[derive(Debug)]
 pub struct SignatureRegistry {
     signature_hash: HashMap<ir::Signature, VMSharedSignatureIndex>,
-    shared_signatures: PrimaryMap<SignatureIndex, VMSharedSignatureIndex>,
 }
 
 impl SignatureRegistry {
+    /// Create a new `SignatureRegistry`.
     pub fn new() -> Self {
         Self {
             signature_hash: HashMap::new(),
-            shared_signatures: PrimaryMap::new(),
         }
     }
 
-    pub fn vmshared_signatures(&mut self) -> *mut VMSharedSignatureIndex {
-        self.shared_signatures
-            .values_mut()
-            .into_slice()
-            .as_mut_ptr()
-    }
-
-    /// Register the given signature.
-    pub fn register(&mut self, sig_index: SignatureIndex, sig: &ir::Signature) {
-        // TODO: Refactor this interface so that we're not passing in redundant
-        // information.
-        debug_assert_eq!(sig_index.index(), self.shared_signatures.len());
-        use cranelift_entity::EntityRef;
-
+    /// Register a signature and return its unique index.
+    pub fn register(&mut self, sig: &ir::Signature) -> VMSharedSignatureIndex {
         let len = self.signature_hash.len();
-        let sig_id = match self.signature_hash.entry(sig.clone()) {
+        match self.signature_hash.entry(sig.clone()) {
             hash_map::Entry::Occupied(entry) => *entry.get(),
             hash_map::Entry::Vacant(entry) => {
                 let sig_id = VMSharedSignatureIndex::new(cast::u32(len).unwrap());
                 entry.insert(sig_id);
                 sig_id
             }
-        };
-        self.shared_signatures.push(sig_id);
-    }
-
-    /// Return the identifying runtime index for the given signature.
-    pub fn lookup(&mut self, sig_index: SignatureIndex) -> VMSharedSignatureIndex {
-        self.shared_signatures[sig_index]
+        }
     }
 }