Add an EntityMap::get_or_default() method.

This covers a common pattern for secondary entity maps: Get the value in
the map or the default value for out-of-range keys.

lib/cretonne/src/binemit/relaxation.rs

@@ -64,7 +64,7 @@ pub fn relax_branches(func: &mut Function, isa: &TargetIsa) {
             }
 
             while let Some(inst) = pos.next_inst() {
-                let enc = func.encodings.get(inst).cloned().unwrap_or_default();
+                let enc = func.encodings.get_or_default(inst);
                 let size = encinfo.bytes(enc);
 
                 // See if this might be a branch that is out of range.

lib/cretonne/src/entity_map.rs

@@ -148,6 +148,11 @@ impl<K, V> EntityMap<K, V>
         }
         &mut self.elems[k.index()]
     }
+
+    /// Get the element at `k` or the default value if `k` is out of range.
+    pub fn get_or_default(&self, k: K) -> V {
+        self.elems.get(k.index()).cloned().unwrap_or_default()
+    }
 }
 
 /// Immutable indexing into an `EntityMap`.

lib/cretonne/src/verifier/mod.rs

@@ -668,11 +668,7 @@ impl<'a> Verifier<'a> {
     /// instruction (if any) matches how the ISA would encode it.
     fn verify_encoding(&self, inst: Inst) -> Result {
         if let Some(isa) = self.isa {
-            let encoding = self.func
-                .encodings
-                .get(inst)
-                .cloned()
-                .unwrap_or_default();
+            let encoding = self.func.encodings.get_or_default(inst);
             if encoding.is_legal() {
                 let verify_encoding =
                     isa.encode(&self.func.dfg,

lib/cretonne/src/write.rs

@@ -189,13 +189,7 @@ fn write_instruction(w: &mut Write,
             if !func.locations.is_empty() {
                 let regs = isa.register_info();
                 for &r in func.dfg.inst_results(inst) {
-                    write!(s,
-                           ",{}",
-                           func.locations
-                               .get(r)
-                               .cloned()
-                               .unwrap_or_default()
-                               .display(&regs))?
+                    write!(s, ",{}", func.locations.get_or_default(r).display(&regs))?
                 }
             }
             write!(s, "]")?;

src/filetest/binemit.rs

@@ -106,10 +106,7 @@ impl SubTest for TestBinEmit {
         // Give an encoding to any instruction that doesn't already have one.
         for ebb in func.layout.ebbs() {
             for inst in func.layout.ebb_insts(ebb) {
-                if !func.encodings
-                        .get(inst)
-                        .map(|e| e.is_legal())
-                        .unwrap_or(false) {
+                if !func.encodings.get_or_default(inst).is_legal() {
                     if let Ok(enc) = isa.encode(&func.dfg,
                                                 &func.dfg[inst],
                                                 func.dfg.ctrl_typevar(inst)) {
@@ -157,7 +154,7 @@ impl SubTest for TestBinEmit {
                        ebb);
             for inst in func.layout.ebb_insts(ebb) {
                 sink.text.clear();
-                let enc = func.encodings.get(inst).cloned().unwrap_or_default();
+                let enc = func.encodings.get_or_default(inst);
 
                 // Send legal encodings into the emitter.
                 if enc.is_legal() {