Lint fixes (#99)

* Replace a single-character string literal with a character literal.

* Use is_some() instead of comparing with Some(_).

* Add code-quotes around type names in comments.

* Use !...is_empty() instead of len() != 0.

* Tidy up redundant returns.

* Remove redundant .clone() calls.

* Remove unnecessary explicit lifetime parameters.

* Tidy up unnecessary '&'s.

* Add parens to make operator precedence explicit.

* Use debug_assert_eq instead of debug_assert with ==.

* Replace a &Vec argument with a &[...].

* Replace `a = a op b` with `a op= b`.

* Avoid unnecessary closures.

* Avoid .iter() and .iter_mut() for iterating over containers.

* Remove unneeded qualification.

lib/cretonne/src/simple_gvn.rs

@@ -16,7 +16,7 @@ fn trivially_unsafe_for_gvn(opcode: Opcode) -> bool {
 pub fn do_simple_gvn(func: &mut Function, cfg: &mut ControlFlowGraph) {
     let mut visible_values: HashMap<InstructionData, Inst> = HashMap::new();
 
-    let domtree = DominatorTree::with_function(func, &cfg);
+    let domtree = DominatorTree::with_function(func, cfg);
 
     // Visit EBBs in a reverse post-order.
     let mut pos = Cursor::new(&mut func.layout);
@@ -47,7 +47,7 @@ pub fn do_simple_gvn(func: &mut Function, cfg: &mut ControlFlowGraph) {
             use std::collections::hash_map::Entry::*;
             match entry {
                 Occupied(mut entry) => {
-                    if domtree.dominates(*entry.get(), inst, &pos.layout) {
+                    if domtree.dominates(*entry.get(), inst, pos.layout) {
                         func.dfg.replace_with_aliases(inst, *entry.get());
                         pos.remove_inst_and_step_back();
                     } else {