Improve handling of strings for backtraces (#843)

* Improve handling of strings for backtraces

Largely avoid storing strings at all in the `wasmtime-*` internal
crates, and instead only store strings in a separate global cache
specific to the `wasmtime` crate itself. This global cache is inserted
and removed from dynamically as modules are created and deallocated, and
the global cache is consulted whenever a `Trap` is created to
symbolicate any wasm frames.

This also avoids the need to thread `module_name` through the jit crates
and back, and additionally removes the need for `ModuleSyncString`.

* Run rustfmt

crates/runtime/src/instance.rs

@@ -23,6 +23,7 @@ use std::collections::HashSet;
 use std::convert::TryFrom;
 use std::ptr::NonNull;
 use std::rc::Rc;
+use std::sync::Arc;
 use std::{mem, ptr, slice};
 use thiserror::Error;
 use wasmtime_environ::entity::{BoxedSlice, EntityRef, PrimaryMap};
@@ -288,7 +289,7 @@ pub(crate) struct Instance {
     mmap: Mmap,
 
     /// The `Module` this `Instance` was instantiated from.
-    module: Rc<Module>,
+    module: Arc<Module>,
 
     /// Offsets in the `vmctx` region.
     offsets: VMOffsets,
@@ -748,7 +749,7 @@ impl InstanceHandle {
 
     /// Create a new `InstanceHandle` pointing at a new `Instance`.
     pub fn new(
-        module: Rc<Module>,
+        module: Arc<Module>,
         finished_functions: BoxedSlice<DefinedFuncIndex, *const VMFunctionBody>,
         imports: Imports,
         data_initializers: &[DataInitializer<'_>],
@@ -895,8 +896,8 @@ impl InstanceHandle {
     }
 
     /// Return a reference-counting pointer to a module.
-    pub fn module(&self) -> Rc<Module> {
-        self.instance().module.clone()
+    pub fn module(&self) -> &Arc<Module> {
+        &self.instance().module
     }
 
     /// Return a reference to a module.
@@ -1110,7 +1111,7 @@ fn lookup_by_declaration(
 }
 
 fn check_table_init_bounds(instance: &mut Instance) -> Result<(), InstantiationError> {
-    let module = Rc::clone(&instance.module);
+    let module = Arc::clone(&instance.module);
     for init in &module.table_elements {
         let start = get_table_init_start(init, instance);
         let slice = get_table_slice(
@@ -1234,7 +1235,7 @@ fn get_table_slice<'instance>(
 /// Initialize the table memory from the provided initializers.
 fn initialize_tables(instance: &mut Instance) -> Result<(), InstantiationError> {
     let vmctx: *mut VMContext = instance.vmctx_mut();
-    let module = Rc::clone(&instance.module);
+    let module = Arc::clone(&instance.module);
     for init in &module.table_elements {
         let start = get_table_init_start(init, instance);
         let slice = get_table_slice(
@@ -1311,7 +1312,7 @@ fn create_globals(module: &Module) -> BoxedSlice<DefinedGlobalIndex, VMGlobalDef
 }
 
 fn initialize_globals(instance: &mut Instance) {
-    let module = Rc::clone(&instance.module);
+    let module = Arc::clone(&instance.module);
     let num_imports = module.imported_globals.len();
     for (index, global) in module.globals.iter().skip(num_imports) {
         let def_index = module.defined_global_index(index).unwrap();

crates/runtime/src/jit_function_registry.rs

@@ -3,7 +3,7 @@
 use lazy_static::lazy_static;
 use std::collections::BTreeMap;
 use std::sync::{Arc, RwLock};
-use wasmtime_environ::ModuleSyncString;
+use wasmtime_environ::wasm::FuncIndex;
 
 lazy_static! {
     static ref REGISTRY: RwLock<JITFunctionRegistry> = RwLock::new(JITFunctionRegistry::default());
@@ -11,20 +11,8 @@ lazy_static! {
 
 #[derive(Clone)]
 pub struct JITFunctionTag {
-    pub module_id: ModuleSyncString,
-    pub func_index: usize,
-    pub func_name: ModuleSyncString,
-}
-
-impl std::fmt::Debug for JITFunctionTag {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        if let Some(ref module_id) = self.module_id.get() {
-            write!(f, "{}", module_id)?;
-        } else {
-            write!(f, "(module)")?;
-        }
-        write!(f, ":{}", self.func_index)
-    }
+    pub module_id: usize,
+    pub func_index: FuncIndex,
 }
 
 struct JITFunctionRegistry {