Add caching. (#134)

* Allow a module to have a different signature registry than the process-specific

* Add core ability to build compiled code caches

* Remove timing printouts

* Serialize/Deserialize memories to reduce copies

* Work more on api

* Relocate local functions relatively before external functions

* Fix incorrect definition in test

* merge errors caused by merge

* Fix emscripten compile

* Fix review comments

lib/clif-backend/src/cache.rs

@@ -0,0 +1,46 @@
+use crate::relocation::{ExternalRelocation, TrapSink};
+
+use hashbrown::HashMap;
+use wasmer_runtime_core::{
+    backend::sys::Memory,
+    cache::{Cache, Error},
+    module::ModuleInfo,
+    structures::Map,
+    types::{LocalFuncIndex, SigIndex},
+};
+
+use serde_bench::{deserialize, serialize};
+
+#[derive(Serialize, Deserialize)]
+pub struct TrampolineCache {
+    #[serde(with = "serde_bytes")]
+    pub code: Vec<u8>,
+    pub offsets: HashMap<SigIndex, usize>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct BackendCache {
+    pub external_relocs: Map<LocalFuncIndex, Box<[ExternalRelocation]>>,
+    pub offsets: Map<LocalFuncIndex, usize>,
+    pub trap_sink: TrapSink,
+    pub trampolines: TrampolineCache,
+}
+
+impl BackendCache {
+    pub fn from_cache(cache: Cache) -> Result<(ModuleInfo, Memory, Self), Error> {
+        let (info, backend_data, compiled_code) = cache.consume();
+
+        let backend_cache = deserialize(backend_data.as_slice())
+            .map_err(|e| Error::DeserializeError(e.to_string()))?;
+
+        Ok((info, compiled_code, backend_cache))
+    }
+
+    pub fn into_backend_data(self) -> Result<Vec<u8>, Error> {
+        let mut buffer = Vec::new();
+
+        serialize(&mut buffer, &self).map_err(|e| Error::SerializeError(e.to_string()))?;
+
+        Ok(buffer)
+    }
+}