Document lifetimes of StringRef

Author: math-fehr

mlir/include/mlir/IR/AttributeSupport.h

@@ -150,7 +150,8 @@ class AbstractAttribute {
   /// The unique identifier of the derived Attribute class.
   const TypeID typeID;
 
-  /// The unique name of this type.
+  /// The unique name of this attribute. The string is not owned by the context,
+  /// so the lifetime of this string should outlive the MLIR context.
   const StringRef name;
 };
 

mlir/include/mlir/IR/TypeSupport.h

@@ -149,7 +149,8 @@ class AbstractType {
   /// The unique identifier of the derived Type class.
   const TypeID typeID;
 
-  /// The unique name of this type.
+  /// The unique name of this type. The string is not owned by the context, so
+  /// The lifetime of this string should outlive the MLIR context.
   const StringRef name;
 };
 

mlir/lib/IR/MLIRContext.cpp

@@ -215,7 +215,8 @@ class MLIRContextImpl {
   /// This is a mapping from type name to the abstract type describing it.
   /// It is used by `AbstractType::lookup` to get an `AbstractType` from a name.
   /// As this map needs to be populated before `StringAttr` is loaded, we
-  /// cannot use `StringAttr` as the key.
+  /// cannot use `StringAttr` as the key. The context does not take ownership
+  /// of the key, so the `StringRef` must outlive the context.
   llvm::DenseMap<StringRef, AbstractType *> nameToType;
 
   /// Cached Type Instances.
@@ -246,7 +247,8 @@ class MLIRContextImpl {
   /// it. It is used by `AbstractType::lookup` to get an `AbstractType` from a
   /// name.
   /// As this map needs to be populated before `StringAttr` is loaded, we
-  /// cannot use `StringAttr` as the key.
+  /// cannot use `StringAttr` as the key. The context does not take ownership
+  /// of the key, so the `StringRef` must outlive the context.
   llvm::DenseMap<StringRef, AbstractAttribute *> nameToAttribute;
 
   /// Cached Attribute Instances.