Refactor how signatures/trampolines are stored in Store

This commit refactors where trampolines and signature information is
stored within a `Store`, namely moving them from
`wasmtime_runtime::Instance` instead to `Store` itself. The goal here is
to remove an allocation inside of an `Instance` and make them a bit
cheaper to create. Additionally this should open up future possibilities
like not creating duplicate trampolines for signatures already in the
`Store` when using `Func::new`.

crates/runtime/src/instance.rs

@@ -11,7 +11,7 @@ use crate::traphandlers::Trap;
 use crate::vmcontext::{
     VMBuiltinFunctionsArray, VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport,
     VMGlobalDefinition, VMGlobalImport, VMInterrupts, VMMemoryDefinition, VMMemoryImport,
-    VMSharedSignatureIndex, VMTableDefinition, VMTableImport, VMTrampoline,
+    VMSharedSignatureIndex, VMTableDefinition, VMTableImport,
 };
 use crate::{ExportFunction, ExportGlobal, ExportMemory, ExportTable};
 use memoffset::offset_of;
@@ -62,9 +62,6 @@ pub(crate) struct Instance {
     /// get removed. A missing entry is considered equivalent to an empty slice.
     passive_data: RefCell<HashMap<DataIndex, Arc<[u8]>>>,
 
-    /// Pointers to trampoline functions used to enter particular signatures
-    trampolines: HashMap<VMSharedSignatureIndex, VMTrampoline>,
-
     /// Hosts can store arbitrary per-instance information here.
     host_state: Box<dyn Any>,
 
@@ -815,10 +812,9 @@ impl InstanceHandle {
         module: Arc<Module>,
         code: Arc<dyn Any>,
         finished_functions: &PrimaryMap<DefinedFuncIndex, *mut [VMFunctionBody]>,
-        trampolines: HashMap<VMSharedSignatureIndex, VMTrampoline>,
         imports: Imports,
         mem_creator: Option<&dyn RuntimeMemoryCreator>,
-        vmshared_signatures: BoxedSlice<SignatureIndex, VMSharedSignatureIndex>,
+        lookup_shared_signature: &dyn Fn(SignatureIndex) -> VMSharedSignatureIndex,
         host_state: Box<dyn Any>,
         interrupts: *const VMInterrupts,
         externref_activations_table: *mut VMExternRefActivationsTable,
@@ -857,7 +853,6 @@ impl InstanceHandle {
                 tables,
                 passive_elements: Default::default(),
                 passive_data,
-                trampolines,
                 host_state,
                 vmctx: VMContext {},
             };
@@ -873,12 +868,12 @@ impl InstanceHandle {
         };
         let instance = handle.instance();
 
-        debug_assert_eq!(vmshared_signatures.len(), handle.module().signatures.len());
-        ptr::copy(
-            vmshared_signatures.values().as_slice().as_ptr(),
-            instance.signature_ids_ptr() as *mut VMSharedSignatureIndex,
-            vmshared_signatures.len(),
-        );
+        let mut ptr = instance.signature_ids_ptr();
+        for (signature, _) in handle.module().signatures.iter() {
+            *ptr = lookup_shared_signature(signature);
+            ptr = ptr.add(1);
+        }
+
         debug_assert_eq!(imports.functions.len(), handle.module().num_imported_funcs);
         ptr::copy(
             imports.functions.as_ptr(),
@@ -1128,11 +1123,6 @@ impl InstanceHandle {
         self.instance().get_defined_table(index)
     }
 
-    /// Gets the trampoline pre-registered for a particular signature
-    pub fn trampoline(&self, sig: VMSharedSignatureIndex) -> Option<VMTrampoline> {
-        self.instance().trampolines.get(&sig).cloned()
-    }
-
     /// Return a reference to the contained `Instance`.
     pub(crate) fn instance(&self) -> &Instance {
         unsafe { &*(self.instance as *const Instance) }

crates/runtime/src/lib.rs

@@ -28,7 +28,6 @@ mod instance;
 mod jit_int;
 mod memory;
 mod mmap;
-mod sig_registry;
 mod table;
 mod traphandlers;
 mod vmcontext;
@@ -43,7 +42,6 @@ pub use crate::instance::{InstanceHandle, InstantiationError, LinkError};
 pub use crate::jit_int::GdbJitImageRegistration;
 pub use crate::memory::{RuntimeLinearMemory, RuntimeMemoryCreator};
 pub use crate::mmap::Mmap;
-pub use crate::sig_registry::SignatureRegistry;
 pub use crate::table::{Table, TableElement};
 pub use crate::traphandlers::{
     catch_traps, init_traps, raise_lib_trap, raise_user_trap, resume_panic, SignalHandler, Trap,

crates/runtime/src/sig_registry.rs

@@ -1,87 +0,0 @@
-//! Implement a registry of function signatures, for fast indirect call
-//! signature checking.
-
-use crate::vmcontext::VMSharedSignatureIndex;
-use more_asserts::assert_lt;
-use std::collections::{hash_map, HashMap};
-use std::convert::TryFrom;
-use wasmtime_environ::{ir, wasm::WasmFuncType};
-
-/// 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, Default)]
-pub struct SignatureRegistry {
-    wasm2index: HashMap<WasmFuncType, VMSharedSignatureIndex>,
-
-    // Maps the index to the original Wasm signature.
-    index2wasm: HashMap<VMSharedSignatureIndex, WasmFuncType>,
-
-    // Maps the index to the native signature.
-    index2native: HashMap<VMSharedSignatureIndex, ir::Signature>,
-}
-
-impl SignatureRegistry {
-    /// Register a signature and return its unique index.
-    pub fn register(
-        &mut self,
-        wasm: WasmFuncType,
-        native: ir::Signature,
-    ) -> VMSharedSignatureIndex {
-        let len = self.wasm2index.len();
-
-        match self.wasm2index.entry(wasm.clone()) {
-            hash_map::Entry::Occupied(entry) => *entry.get(),
-            hash_map::Entry::Vacant(entry) => {
-                // Keep `signature_hash` len under 2**32 -- VMSharedSignatureIndex::new(std::u32::MAX)
-                // is reserved for VMSharedSignatureIndex::default().
-                assert_lt!(
-                    len,
-                    std::u32::MAX as usize,
-                    "Invariant check: signature_hash.len() < std::u32::MAX"
-                );
-                let index = VMSharedSignatureIndex::new(u32::try_from(len).unwrap());
-                entry.insert(index);
-                self.index2wasm.insert(index, wasm);
-                self.index2native.insert(index, native);
-                index
-            }
-        }
-    }
-
-    /// Looks up a shared index from the wasm signature itself.
-    pub fn lookup(&self, wasm: &WasmFuncType) -> Option<VMSharedSignatureIndex> {
-        self.wasm2index.get(wasm).cloned()
-    }
-
-    /// Looks up a shared native signature within this registry.
-    ///
-    /// Note that for this operation to be semantically correct the `idx` must
-    /// have previously come from a call to `register` of this same object.
-    pub fn lookup_native(&self, idx: VMSharedSignatureIndex) -> Option<ir::Signature> {
-        self.index2native.get(&idx).cloned()
-    }
-
-    /// Looks up a shared Wasm signature within this registry.
-    ///
-    /// Note that for this operation to be semantically correct the `idx` must
-    /// have previously come from a call to `register` of this same object.
-    pub fn lookup_wasm(&self, idx: VMSharedSignatureIndex) -> Option<WasmFuncType> {
-        self.index2wasm.get(&idx).cloned()
-    }
-
-    /// Looks up both a shared Wasm function signature and its associated native
-    /// `ir::Signature` within this registry.
-    ///
-    /// Note that for this operation to be semantically correct the `idx` must
-    /// have previously come from a call to `register` of this same object.
-    pub fn lookup_wasm_and_native_signatures(
-        &self,
-        idx: VMSharedSignatureIndex,
-    ) -> Option<(WasmFuncType, ir::Signature)> {
-        let wasm = self.lookup_wasm(idx)?;
-        let native = self.lookup_native(idx)?;
-        Some((wasm, native))
-    }
-}

crates/runtime/src/vmcontext.rs

@@ -492,6 +492,11 @@ impl VMSharedSignatureIndex {
     pub fn new(value: u32) -> Self {
         Self(value)
     }
+
+    /// Returns the underlying bits of the index.
+    pub fn bits(&self) -> u32 {
+        self.0
+    }
 }
 
 impl Default for VMSharedSignatureIndex {