Update no_std support.

This `no_std` support isn't complete though, as some dependencies
don't support it.

lib/jit/src/action.rs

@@ -2,11 +2,11 @@
 
 use crate::compiler::Compiler;
 use crate::instantiate::SetupError;
+use core::cmp::max;
+use core::{fmt, mem, ptr, slice};
 use cranelift_codegen::ir;
-use std::cmp::max;
 use std::string::String;
 use std::vec::Vec;
-use std::{fmt, mem, ptr, slice};
 use wasmtime_runtime::{wasmtime_call_trampoline, Export, Instance};
 
 /// A runtime value.

lib/jit/src/code_memory.rs

@@ -1,9 +1,9 @@
 //! Memory management for executable code.
 
+use core::{cmp, mem};
 use region;
 use std::string::String;
 use std::vec::Vec;
-use std::{cmp, mem};
 use wasmtime_runtime::{Mmap, VMFunctionBody};
 
 /// Memory manager for executable code.

lib/jit/src/compiler.rs

@@ -1,5 +1,6 @@
 //! JIT compilation.
 
+use super::HashMap;
 use crate::code_memory::CodeMemory;
 use crate::instantiate::SetupError;
 use crate::target_tunables::target_tunables;
@@ -11,7 +12,6 @@ use cranelift_entity::PrimaryMap;
 use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use cranelift_wasm::DefinedFuncIndex;
 use std::boxed::Box;
-use std::collections::HashMap;
 use std::string::String;
 use std::vec::Vec;
 use wasmtime_environ::cranelift;
@@ -95,7 +95,7 @@ impl Compiler {
         signature: &ir::Signature,
         value_size: usize,
     ) -> Result<*const VMFunctionBody, SetupError> {
-        use std::collections::hash_map::Entry::{Occupied, Vacant};
+        use super::hash_map::Entry::{Occupied, Vacant};
         Ok(match self.trampoline_park.entry(callee_address) {
             Occupied(entry) => *entry.get(),
             Vacant(entry) => {

lib/jit/src/lib.rs

@@ -21,18 +21,26 @@
         clippy::use_self
     )
 )]
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 #![cfg_attr(not(feature = "std"), feature(alloc))]
 
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc as std;
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[cfg(not(feature = "std"))]
+use hashmap_core::{map as hash_map, HashMap};
+#[cfg(feature = "std")]
+use std::collections::{hash_map, HashMap};
+
 #[macro_use]
 extern crate cranelift_entity;
 
-use region;
-
-#[cfg(not(feature = "std"))]
-#[macro_use]
-extern crate alloc;
 use failure;
+use region;
 
 #[macro_use]
 extern crate failure_derive;
@@ -57,10 +65,3 @@ pub use crate::target_tunables::target_tunables;
 // Re-export `Instance` so that users won't need to separately depend on
 // wasmtime-runtime in common cases.
 pub use wasmtime_runtime::{Instance, InstantiationError};
-
-#[cfg(not(feature = "std"))]
-mod std {
-    pub use alloc::{boxed, rc, string, vec};
-    pub use core::*;
-    pub use core::{i32, str, u32};
-}

lib/jit/src/link.rs

@@ -1,10 +1,10 @@
 //! Linking for JIT-compiled code.
 
 use crate::resolver::Resolver;
+use core::ptr::write_unaligned;
 use cranelift_codegen::binemit::Reloc;
 use cranelift_entity::PrimaryMap;
 use cranelift_wasm::{DefinedFuncIndex, Global, GlobalInit, Memory, Table, TableElementType};
-use std::ptr::write_unaligned;
 use std::vec::Vec;
 use wasmtime_environ::{
     MemoryPlan, MemoryStyle, Module, Relocation, RelocationTarget, Relocations, TablePlan,

lib/jit/src/namespace.rs

@@ -2,12 +2,12 @@
 //! to exports. This file provides one possible way to manage multiple instances
 //! and resolve imports to exports among them.
 
+use super::HashMap;
 use crate::action::{get, inspect_memory, invoke};
 use crate::action::{ActionError, ActionOutcome, RuntimeValue};
 use crate::compiler::Compiler;
 use crate::resolver::Resolver;
 use cranelift_entity::PrimaryMap;
-use std::collections::HashMap;
 use std::string::String;
 use wasmtime_runtime::{Export, Instance};
 

lib/jit/src/target_tunables.rs

@@ -1,4 +1,4 @@
-use std::cmp::min;
+use core::cmp::min;
 use target_lexicon::{OperatingSystem, Triple};
 use wasmtime_environ::Tunables;