Fix determinism of compiled modules (#3229)

* Fix determinism of compiled modules

Currently wasmtime's compilation artifacts are not deterministic due to
the usage of `HashMap` during serialization which has randomized order
of its elements. This commit fixes that by switching to a sorted
`BTreeMap` for various maps. A test is also added to ensure determinism.

If in the future the performance of `BTreeMap` is not as good as
`HashMap` for some of these cases we can implement a fancier
`serialize_with`-style solution where we sort keys during serialization,
but only during serialization and otherwise use a `HashMap`.

* fix lightbeam

crates/environ/src/compilation.rs

@@ -9,7 +9,7 @@ use anyhow::Result;
 use serde::{Deserialize, Serialize};
 use std::any::Any;
 use std::borrow::Cow;
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 use std::fmt;
 use thiserror::Error;
 
@@ -204,10 +204,10 @@ pub trait Compiler: Send + Sync {
     fn triple(&self) -> &target_lexicon::Triple;
 
     /// Returns a list of configured settings for this compiler.
-    fn flags(&self) -> HashMap<String, FlagValue>;
+    fn flags(&self) -> BTreeMap<String, FlagValue>;
 
     /// Same as [`Compiler::flags`], but ISA-specific (a cranelift-ism)
-    fn isa_flags(&self) -> HashMap<String, FlagValue>;
+    fn isa_flags(&self) -> BTreeMap<String, FlagValue>;
 }
 
 /// Value of a configured setting for a [`Compiler`]

crates/environ/src/module.rs

@@ -3,7 +3,7 @@
 use crate::{EntityRef, PrimaryMap, Tunables};
 use indexmap::IndexMap;
 use serde::{Deserialize, Serialize};
-use std::collections::{HashMap, HashSet};
+use std::collections::{BTreeMap, BTreeSet};
 use std::convert::TryFrom;
 use std::sync::Arc;
 use wasmtime_types::*;
@@ -349,17 +349,17 @@ pub struct Module {
     pub passive_elements: Vec<Box<[FuncIndex]>>,
 
     /// The map from passive element index (element segment index space) to index in `passive_elements`.
-    pub passive_elements_map: HashMap<ElemIndex, usize>,
+    pub passive_elements_map: BTreeMap<ElemIndex, usize>,
 
     /// WebAssembly passive data segments.
     #[serde(with = "passive_data_serde")]
     pub passive_data: Vec<Arc<[u8]>>,
 
     /// The map from passive data index (data segment index space) to index in `passive_data`.
-    pub passive_data_map: HashMap<DataIndex, usize>,
+    pub passive_data_map: BTreeMap<DataIndex, usize>,
 
     /// WebAssembly function names.
-    pub func_names: HashMap<FuncIndex, String>,
+    pub func_names: BTreeMap<FuncIndex, String>,
 
     /// Types declared in the wasm module.
     pub types: PrimaryMap<TypeIndex, ModuleType>,
@@ -396,7 +396,7 @@ pub struct Module {
 
     /// The set of defined functions within this module which are located in
     /// element segments.
-    pub possibly_exported_funcs: HashSet<DefinedFuncIndex>,
+    pub possibly_exported_funcs: BTreeSet<DefinedFuncIndex>,
 }
 
 /// Initialization routines for creating an instance, encompassing imports,