Don't go through the formatting infrastructure just to get the name of a phase

compiler/rustc_middle/src/mir/syntax.rs

@@ -89,6 +89,19 @@ pub enum MirPhase {
     Runtime(RuntimePhase),
 }
 
+impl MirPhase {
+    pub fn name(&self) -> &'static str {
+        match *self {
+            MirPhase::Built => "built",
+            MirPhase::Analysis(AnalysisPhase::Initial) => "analysis",
+            MirPhase::Analysis(AnalysisPhase::PostCleanup) => "analysis-post-cleanup",
+            MirPhase::Runtime(RuntimePhase::Initial) => "runtime",
+            MirPhase::Runtime(RuntimePhase::PostCleanup) => "runtime-post-cleanup",
+            MirPhase::Runtime(RuntimePhase::Optimized) => "runtime-optimized",
+        }
+    }
+}
+
 /// See [`MirPhase::Analysis`].
 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[derive(HashStable)]