Update to use newer Rust features.

This re-introduces several cleanups that we previously deferred for not
supporting Rust 1.25.

lib/codegen/src/context.rs

@@ -101,14 +101,7 @@ impl Context {
         let code_size = self.compile(isa)?;
         let old_len = mem.len();
         mem.resize(old_len + code_size as usize, 0);
-        unsafe {
-            self.emit_to_memory(
-                isa,
-                mem.as_mut_ptr().offset(old_len as isize),
-                relocs,
-                traps,
-            )
-        };
+        unsafe { self.emit_to_memory(isa, mem.as_mut_ptr().add(old_len), relocs, traps) };
         Ok(())
     }
 

lib/codegen/src/ir/dfg.rs

@@ -127,7 +127,7 @@ fn maybe_resolve_aliases(values: &PrimaryMap<Value, ValueData>, value: Value) ->
     let mut v = value;
 
     // Note that values may be empty here.
-    for _ in 0..values.len() + 1 {
+    for _ in 0..=values.len() {
         if let ValueData::Alias { original, .. } = values[v] {
             v = original;
         } else {

lib/codegen/src/lib.rs

@@ -8,8 +8,6 @@
     plugin(clippy(conf_file = "../../clippy.toml"))
 )]
 #![cfg_attr(feature="cargo-clippy", allow(
-// This requires Rust 1.27 or later.
-                duration_subsec,
 // Produces only a false positive:
                 while_let_loop,
 // Produces many false positives, but did produce some valid lints, now fixed:

lib/codegen/src/timing.rs

@@ -154,7 +154,7 @@ mod details {
                 fn fmtdur(mut dur: Duration, f: &mut fmt::Formatter) -> fmt::Result {
                     // Round to nearest ms by adding 500us.
                     dur += Duration::new(0, 500_000);
-                    let ms = dur.subsec_nanos() / 1_000_000;
+                    let ms = dur.subsec_millis();
                     write!(f, "{:4}.{:03} ", dur.as_secs(), ms)
                 }