Partial hashing of module for faster caching (#221)

* Simple module compilation cache

* Fix base64 encoding bug

* Use warn! everywhere in cache system

* Remove unused import

* Temporary workaround for long path on Windows

* Remove unused import for non-windows builds

* Add command line argument to enable cache system + apply minor review feedback

* Initial implementation of partial module hashing

* Proper module hashing for the cache

* Use newer version of cranelift

wasmtime-environ/src/module_environ.rs

@@ -10,12 +10,12 @@ use cranelift_wasm::{
     self, translate_module, DefinedFuncIndex, FuncIndex, Global, GlobalIndex, Memory, MemoryIndex,
     SignatureIndex, Table, TableIndex, WasmResult,
 };
-use sha2::{Digest, Sha256};
 use std::boxed::Box;
 use std::string::String;
 use std::vec::Vec;
 
 /// Contains function data: byte code and its offset in the module.
+#[derive(Hash)]
 pub struct FunctionBodyData<'a> {
     /// Body byte code.
     pub data: &'a [u8],
@@ -80,11 +80,6 @@ impl<'data> ModuleEnvironment<'data> {
     pub fn translate(mut self, data: &'data [u8]) -> WasmResult<ModuleTranslation<'data>> {
         translate_module(data, &mut self)?;
 
-        // TODO: this is temporary workaround and will be replaced with derive macro.
-        let mut hasher = Sha256::new();
-        hasher.input(data);
-        self.result.module.hash = Some(hasher.result().into());
-
         Ok(self.result)
     }
 }