Remove insert_noop.

Because it's as useless as its name suggests.

This commit also renames `UndoLog::Noop` as `UndoLog::Purged`, because
(a) that's a more descriptive name and (b) it matches the name used in
similar code in `librustc/infer/region_constraints/mod.rs`.

Author: nnethercote

src/librustc/traits/project.rs

@@ -1714,12 +1714,8 @@ impl<'tcx> ProjectionCache<'tcx> {
     /// to be a NormalizedTy.
     pub fn complete_normalized(&mut self, key: ProjectionCacheKey<'tcx>, ty: &NormalizedTy<'tcx>) {
         // We want to insert `ty` with no obligations. If the existing value
-        // already has no obligations (as is common) we can use `insert_noop`
-        // to do a minimal amount of work -- the HashMap insertion is skipped,
-        // and minimal changes are made to the undo log.
-        if ty.obligations.is_empty() {
-            self.map.insert_noop();
-        } else {
+        // already has no obligations (as is common) we don't insert anything.
+        if !ty.obligations.is_empty() {
             self.map.insert(key, ProjectionCacheEntry::NormalizedTy(Normalized {
                 value: ty.value,
                 obligations: vec![]

src/librustc_data_structures/snapshot_map/mod.rs

@@ -44,7 +44,7 @@ enum UndoLog<K, V> {
     CommittedSnapshot,
     Inserted(K),
     Overwrite(K, V),
-    Noop,
+    Purged,
 }
 
 impl<K, V> SnapshotMap<K, V>
@@ -72,12 +72,6 @@ impl<K, V> SnapshotMap<K, V>
         }
     }
 
-    pub fn insert_noop(&mut self) {
-        if !self.undo_log.is_empty() {
-            self.undo_log.push(UndoLog::Noop);
-        }
-    }
-
     pub fn remove(&mut self, key: K) -> bool {
         match self.map.remove(&key) {
             Some(old_value) => {
@@ -128,13 +122,13 @@ impl<K, V> SnapshotMap<K, V>
             let reverse = match self.undo_log[i] {
                 UndoLog::OpenSnapshot => false,
                 UndoLog::CommittedSnapshot => false,
-                UndoLog::Noop => false,
+                UndoLog::Purged => false,
                 UndoLog::Inserted(ref k) => should_revert_key(k),
                 UndoLog::Overwrite(ref k, _) => should_revert_key(k),
             };
 
             if reverse {
-                let entry = mem::replace(&mut self.undo_log[i], UndoLog::Noop);
+                let entry = mem::replace(&mut self.undo_log[i], UndoLog::Purged);
                 self.reverse(entry);
             }
         }
@@ -171,7 +165,7 @@ impl<K, V> SnapshotMap<K, V>
                 self.map.insert(key, old_value);
             }
 
-            UndoLog::Noop => {}
+            UndoLog::Purged => {}
         }
     }
 }