[clippy] Fix a few clippy issues in lib/codegen/;

- don't generate "&& true" when generating instruction eq() fn;
- use more Self;
- use subsec_millis instead of subsec_nanos and divide;
- coalesce two ifs;

lib/codegen/src/fx.rs

@@ -50,8 +50,8 @@ const K: usize = 0x517cc1b727220a95;
 
 impl Default for FxHasher {
     #[inline]
-    fn default() -> FxHasher {
-        FxHasher { hash: 0 }
+    fn default() -> Self {
+        Self { hash: 0 }
     }
 }
 

lib/codegen/src/ir/extname.rs

@@ -111,7 +111,7 @@ impl FromStr for ExternalName {
         // Try to parse as a libcall name, otherwise it's a test case.
         match s.parse() {
             Ok(lc) => Ok(ExternalName::LibCall(lc)),
-            Err(_) => Ok(ExternalName::testcase(s.as_bytes())),
+            Err(_) => Ok(Self::testcase(s.as_bytes())),
         }
     }
 }

lib/codegen/src/timing.rs

@@ -154,8 +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;
-                    write!(f, "{:4}.{:03} ", dur.as_secs(), ms)
+                    write!(f, "{:4}.{:03} ", dur.as_secs(), dur.subsec_millis())
                 }
 
                 fmtdur(time.total, f)?;

lib/codegen/src/verifier/locations.rs

@@ -69,10 +69,8 @@ impl<'a> LocationVerifier<'a> {
                 let opcode = dfg[inst].opcode();
                 if opcode.is_return() {
                     self.check_return_abi(inst, &divert)?;
-                } else if opcode.is_branch() {
-                    if !divert.is_empty() {
-                        self.check_cfg_edges(inst, &divert)?;
-                    }
+                } else if opcode.is_branch() && !divert.is_empty() {
+                    self.check_cfg_edges(inst, &divert)?;
                 }
 
                 self.update_diversions(inst, &mut divert)?;