Use &'static str instead of String for target features.

It's a more precise type -- these are static values. Also it avoids
unnecessary allocations.

Author: nnethercote

crates/nvvm/src/lib.rs

@@ -339,7 +339,7 @@ pub enum NvvmArch {
 
 impl Display for NvvmArch {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.write_str(&self.target_feature())
+        f.write_str(self.target_feature())
     }
 }
 
@@ -435,40 +435,40 @@ impl NvvmArch {
     }
 
     /// Get the target feature string (e.g., "compute_35" for Compute35, "compute_90a" for Compute90a)
-    pub fn target_feature(&self) -> String {
+    pub fn target_feature(&self) -> &'static str {
         match self {
-            Self::Compute35 => "compute_35".to_string(),
-            Self::Compute37 => "compute_37".to_string(),
-            Self::Compute50 => "compute_50".to_string(),
-            Self::Compute52 => "compute_52".to_string(),
-            Self::Compute53 => "compute_53".to_string(),
-            Self::Compute60 => "compute_60".to_string(),
-            Self::Compute61 => "compute_61".to_string(),
-            Self::Compute62 => "compute_62".to_string(),
-            Self::Compute70 => "compute_70".to_string(),
-            Self::Compute72 => "compute_72".to_string(),
-            Self::Compute75 => "compute_75".to_string(),
-            Self::Compute80 => "compute_80".to_string(),
-            Self::Compute86 => "compute_86".to_string(),
-            Self::Compute87 => "compute_87".to_string(),
-            Self::Compute89 => "compute_89".to_string(),
-            Self::Compute90 => "compute_90".to_string(),
-            Self::Compute90a => "compute_90a".to_string(),
-            Self::Compute100 => "compute_100".to_string(),
-            Self::Compute100f => "compute_100f".to_string(),
-            Self::Compute100a => "compute_100a".to_string(),
-            Self::Compute101 => "compute_101".to_string(),
-            Self::Compute101f => "compute_101f".to_string(),
-            Self::Compute101a => "compute_101a".to_string(),
-            Self::Compute103 => "compute_103".to_string(),
-            Self::Compute103f => "compute_103f".to_string(),
-            Self::Compute103a => "compute_103a".to_string(),
-            Self::Compute120 => "compute_120".to_string(),
-            Self::Compute120f => "compute_120f".to_string(),
-            Self::Compute120a => "compute_120a".to_string(),
-            Self::Compute121 => "compute_121".to_string(),
-            Self::Compute121f => "compute_121f".to_string(),
-            Self::Compute121a => "compute_121a".to_string(),
+            Self::Compute35 => "compute_35",
+            Self::Compute37 => "compute_37",
+            Self::Compute50 => "compute_50",
+            Self::Compute52 => "compute_52",
+            Self::Compute53 => "compute_53",
+            Self::Compute60 => "compute_60",
+            Self::Compute61 => "compute_61",
+            Self::Compute62 => "compute_62",
+            Self::Compute70 => "compute_70",
+            Self::Compute72 => "compute_72",
+            Self::Compute75 => "compute_75",
+            Self::Compute80 => "compute_80",
+            Self::Compute86 => "compute_86",
+            Self::Compute87 => "compute_87",
+            Self::Compute89 => "compute_89",
+            Self::Compute90 => "compute_90",
+            Self::Compute90a => "compute_90a",
+            Self::Compute100 => "compute_100",
+            Self::Compute100f => "compute_100f",
+            Self::Compute100a => "compute_100a",
+            Self::Compute101 => "compute_101",
+            Self::Compute101f => "compute_101f",
+            Self::Compute101a => "compute_101a",
+            Self::Compute103 => "compute_103",
+            Self::Compute103f => "compute_103f",
+            Self::Compute103a => "compute_103a",
+            Self::Compute120 => "compute_120",
+            Self::Compute120f => "compute_120f",
+            Self::Compute120a => "compute_120a",
+            Self::Compute121 => "compute_121",
+            Self::Compute121f => "compute_121f",
+            Self::Compute121a => "compute_121a",
         }
     }
 

crates/rustc_codegen_nvvm/src/lib.rs

@@ -149,7 +149,7 @@ impl CodegenBackend for NvvmCodegenBackend {
                     features.extend(
                         arch.all_target_features()
                             .into_iter()
-                            .map(|feature| feature.target_feature()),
+                            .map(|s| s.target_feature().to_string()),
                     );
                     break;
                 }
@@ -238,7 +238,7 @@ impl CodegenBackend for NvvmCodegenBackend {
                 target_features.extend(
                     backend_features
                         .iter()
-                        .map(|f| rustc_span::Symbol::intern(&f.target_feature())),
+                        .map(|f| rustc_span::Symbol::intern(f.target_feature())),
                 );
                 break;
             }

tests/compiletests/src/main.rs

@@ -149,7 +149,7 @@ impl Runner {
             // which offer `// only-S` and `// ignore-S` for any stage ID `S`.
             let stage_id = if variation.name == "default" {
                 // Use the architecture name as the stage ID.
-                arch.clone()
+                arch.to_string()
             } else {
                 // Include the variation name in the stage ID.
                 format!("{}-{}", arch, variation.name)
@@ -161,7 +161,7 @@ impl Runner {
                 &self.deps_target_dir,
                 &self.codegen_backend_path,
                 CUDA_TARGET,
-                &arch,
+                arch,
             );
             let mut flags = test_rustc_flags(
                 &self.codegen_backend_path,
@@ -174,7 +174,7 @@ impl Runner {
                         .deps_target_dir
                         .join(DepKind::ProcMacro.target_dir_suffix(CUDA_TARGET)),
                 ],
-                &arch,
+                arch,
             );
             flags += variation.extra_flags;