Add lock

include/circt/Support/Namespace.h

@@ -61,7 +61,11 @@ class Namespace {
 
   /// Removes a symbol from the namespace. Returns true if the symbol was
   /// removed, false if the symbol was not found.
-  bool erase(llvm::StringRef symbol) { return nextIndex.erase(symbol); }
+  /// This is only allowed to be called _before_ any call to newName.
+  bool erase(llvm::StringRef symbol) {
+    assert(!locked && "Cannot erase names from a locked namespace");
+    return nextIndex.erase(symbol);
+  }
 
   /// Empty the namespace.
   void clear() { nextIndex.clear(); }
@@ -74,6 +78,7 @@ class Namespace {
   /// 2. The name is given a `_<n>` suffix where `<n>` is a number starting from
   ///    `0` and incrementing by one each time (`_0`, ...).
   StringRef newName(const Twine &name) {
+    locked = true;
     // Special case the situation where there is no name collision to avoid
     // messing with the SmallString allocation below.
     llvm::SmallString<64> tryName;
@@ -146,6 +151,11 @@ class Namespace {
   // namespace.  It follows that all values less than the "next index" value are
   // already used.
   llvm::StringMap<size_t> nextIndex;
+
+  // When true, no names can be erased from the namespace. This is to prevent
+  // erasing names after they have been used, thus leaving users of the
+  // namespace in an inconsistent state.
+  bool locked = false;
 };
 
 } // namespace circt