Make MachBackend::triple return &Triple

This avoids an unnecessary clone

cranelift/codegen/src/machinst/adapter.rs

@@ -14,16 +14,13 @@ use target_lexicon::Triple;
 /// A wrapper around a `MachBackend` that provides a `TargetIsa` impl.
 pub struct TargetIsaAdapter {
     backend: Box<dyn MachBackend + Send + Sync + 'static>,
-    triple: Triple,
 }
 
 impl TargetIsaAdapter {
     /// Create a new `TargetIsa` wrapper around a `MachBackend`.
     pub fn new<B: MachBackend + Send + Sync + 'static>(backend: B) -> TargetIsaAdapter {
-        let triple = backend.triple();
         TargetIsaAdapter {
             backend: Box::new(backend),
-            triple,
         }
     }
 }
@@ -44,7 +41,7 @@ impl TargetIsa for TargetIsaAdapter {
     }
 
     fn triple(&self) -> &Triple {
-        &self.triple
+        self.backend.triple()
     }
 
     fn flags(&self) -> &Flags {

cranelift/codegen/src/machinst/mod.rs

@@ -390,7 +390,7 @@ pub trait MachBackend {
     fn isa_flags(&self) -> Vec<settings::Value>;
 
     /// Return triple for this backend.
-    fn triple(&self) -> Triple;
+    fn triple(&self) -> &Triple;
 
     /// Return name for this backend.
     fn name(&self) -> &'static str;