Remove the Context type from wasmtime (#825)

* Remove the `Context` type from `wasmtime`

This hasn't really ended up being used in all that many places and the
dependencies on it were pretty minimal. This commit removes it in favor
of simplifying its various users a bit and/or leveraging the
`Engine`/`Store` structures where possible.

* Run rustfmt

crates/api/src/runtime.rs

@@ -1,4 +1,3 @@
-use crate::context::Context;
 use anyhow::Result;
 use std::cell::RefCell;
 use std::collections::HashMap;
@@ -8,7 +7,7 @@ use wasmtime_environ::{
     ir,
     settings::{self, Configurable},
 };
-use wasmtime_jit::{CompilationStrategy, Features};
+use wasmtime_jit::{native, CompilationStrategy, Compiler, Features};
 
 // Runtime Environment
 
@@ -297,7 +296,7 @@ pub enum OptLevel {
 /// default settings.
 #[derive(Default, Clone)]
 pub struct Engine {
-    pub(crate) config: Arc<Config>,
+    config: Arc<Config>,
 }
 
 impl Engine {
@@ -308,6 +307,11 @@ impl Engine {
             config: Arc::new(config.clone()),
         }
     }
+
+    /// Returns the configuration settings that this engine is using.
+    pub fn config(&self) -> &Config {
+        &self.config
+    }
 }
 
 // Store
@@ -337,7 +341,7 @@ pub struct Store {
 
 struct StoreInner {
     engine: Engine,
-    context: Context,
+    compiler: RefCell<Compiler>,
     global_exports: Rc<RefCell<HashMap<String, Option<wasmtime_runtime::Export>>>>,
     signature_cache: RefCell<HashMap<wasmtime_runtime::VMSharedSignatureIndex, ir::Signature>>,
 }
@@ -345,10 +349,12 @@ struct StoreInner {
 impl Store {
     /// Creates a new store to be associated with the given [`Engine`].
     pub fn new(engine: &Engine) -> Store {
+        let isa = native::builder().finish(settings::Flags::new(engine.config.flags.clone()));
+        let compiler = Compiler::new(isa, engine.config.strategy);
         Store {
             inner: Rc::new(StoreInner {
                 engine: engine.clone(),
-                context: Context::new(&engine.config),
+                compiler: RefCell::new(compiler),
                 global_exports: Rc::new(RefCell::new(HashMap::new())),
                 signature_cache: RefCell::new(HashMap::new()),
             }),
@@ -360,8 +366,8 @@ impl Store {
         &self.inner.engine
     }
 
-    pub(crate) fn context(&self) -> &Context {
-        &self.inner.context
+    pub(crate) fn compiler_mut(&self) -> std::cell::RefMut<'_, Compiler> {
+        self.inner.compiler.borrow_mut()
     }
 
     // Specific to wasmtime: hack to pass memory around to wasi
@@ -377,7 +383,7 @@ impl Store {
         signature: &ir::Signature,
     ) -> wasmtime_runtime::VMSharedSignatureIndex {
         use std::collections::hash_map::Entry;
-        let index = self.context().compiler().signatures().register(signature);
+        let index = self.compiler_mut().signatures().register(signature);
         match self.inner.signature_cache.borrow_mut().entry(index) {
             Entry::Vacant(v) => {
                 v.insert(signature.clone());