[MLIR] Cyclic AttrType Replacer

mlir/include/mlir/IR/AttrTypeSubElements.h

@@ -16,6 +16,7 @@
 
 #include "mlir/IR/MLIRContext.h"
 #include "mlir/IR/Visitors.h"
+#include "mlir/Support/CyclicReplacerCache.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include <optional>
@@ -116,9 +117,21 @@ class AttrTypeWalker {
 /// AttrTypeReplacer
 //===----------------------------------------------------------------------===//
 
-/// This class provides a utility for replacing attributes/types, and their sub
-/// elements. Multiple replacement functions may be registered.
-class AttrTypeReplacer {
+namespace detail {
+
+/// This class provides a base utility for replacing attributes/types, and their
+/// sub elements. Multiple replacement functions may be registered.
+///
+/// This base utility is uncached. Users can choose between two cached versions
+/// of this replacer:
+///   * For non-cyclic replacer logic, use `AttrTypeReplacer`.
+///   * For cyclic replacer logic, use `CyclicAttrTypeReplacer`.
+///
+/// Concrete implementations implement the following `replace` entry functions:
+///   * Attribute replace(Attribute attr);
+///   * Type replace(Type type);
+template <typename Concrete>
+class AttrTypeReplacerBase {
 public:
   //===--------------------------------------------------------------------===//
   // Application
@@ -139,12 +152,6 @@ class AttrTypeReplacer {
                                     bool replaceLocs = false,
                                     bool replaceTypes = false);
 
-  /// Replace the given attribute/type, and recursively replace any sub
-  /// elements. Returns either the new attribute/type, or nullptr in the case of
-  /// failure.
-  Attribute replace(Attribute attr);
-  Type replace(Type type);
-
   //===--------------------------------------------------------------------===//
   // Registration
   //===--------------------------------------------------------------------===//
@@ -206,21 +213,114 @@ class AttrTypeReplacer {
     });
   }
 
-private:
-  /// Internal implementation of the `replace` methods above.
-  template <typename T, typename ReplaceFns>
-  T replaceImpl(T element, ReplaceFns &replaceFns);
-
-  /// Replace the sub elements of the given interface.
-  template <typename T>
-  T replaceSubElements(T interface);
+protected:
+  /// Invokes the registered replacement functions from most recently registered
+  /// to least recently registered until a successful replacement is returned.
+  /// Unless skipping is requested, invokes `replace` on sub-elements of the
+  /// current attr/type.
+  Attribute replaceBase(Attribute attr);
+  Type replaceBase(Type type);
 
+private:
   /// The set of replacement functions that map sub elements.
   std::vector<ReplaceFn<Attribute>> attrReplacementFns;
   std::vector<ReplaceFn<Type>> typeReplacementFns;
+};
+
+} // namespace detail
+
+/// This is an attribute/type replacer that is naively cached. It is best used
+/// when the replacer logic is guaranteed to not contain cycles. Otherwise, any
+/// re-occurrence of an in-progress element will be skipped.
+class AttrTypeReplacer : public detail::AttrTypeReplacerBase<AttrTypeReplacer> {
+public:
+  Attribute replace(Attribute attr);
+  Type replace(Type type);
+
+private:
+  /// Shared concrete implementation of the public `replace` functions. Invokes
+  /// `replaceBase` with caching.
+  template <typename T>
+  T cachedReplaceImpl(T element);
+
+  // Stores the opaque pointer of an attribute or type.
+  DenseMap<const void *, const void *> cache;
+};
+
+/// This is an attribute/type replacer that supports custom handling of cycles
+/// in the replacer logic. In addition to registering replacer functions, it
+/// allows registering cycle-breaking functions in the same style.
+class CyclicAttrTypeReplacer
+    : public detail::AttrTypeReplacerBase<CyclicAttrTypeReplacer> {
+public:
+  CyclicAttrTypeReplacer();
 
-  /// The set of cached mappings for attributes/types.
-  DenseMap<const void *, const void *> attrTypeMap;
+  //===--------------------------------------------------------------------===//
+  // Application
+  //===--------------------------------------------------------------------===//
+
+  Attribute replace(Attribute attr);
+  Type replace(Type type);
+
+  //===--------------------------------------------------------------------===//
+  // Registration
+  //===--------------------------------------------------------------------===//
+
+  /// A cycle-breaking function. This is invoked if the same element is asked to
+  /// be replaced again when the first instance of it is still being replaced.
+  /// This function must not perform any more recursive `replace` calls.
+  /// If it is able to break the cycle, it should return a replacement result.
+  /// Otherwise, it can return std::nullopt to defer cycle breaking to the next
+  /// repeated element. However, the user must guarantee that, in any possible
+  /// cycle, there always exists at least one element that can break the cycle.
+  template <typename T>
+  using CycleBreakerFn = std::function<std::optional<T>(T)>;
+
+  /// Register a cycle-breaking function.
+  /// When breaking cycles, the mostly recently added cycle-breaking functions
+  /// will be invoked first.
+  void addCycleBreaker(CycleBreakerFn<Attribute> fn);
+  void addCycleBreaker(CycleBreakerFn<Type> fn);
+
+  /// Register a cycle-breaking function that doesn't match the default
+  /// signature.
+  template <typename FnT,
+            typename T = typename llvm::function_traits<
+                std::decay_t<FnT>>::template arg_t<0>,
+            typename BaseT = std::conditional_t<std::is_base_of_v<Attribute, T>,
+                                                Attribute, Type>>
+  std::enable_if_t<!std::is_same_v<T, BaseT>> addCycleBreaker(FnT &&callback) {
+    addCycleBreaker([callback = std::forward<FnT>(callback)](
+                        BaseT base) -> std::optional<BaseT> {
+      if (auto derived = dyn_cast<T>(base))
+        return callback(derived);
+      return std::nullopt;
+    });
+  }
+
+private:
+  /// Invokes the registered cycle-breaker functions from most recently
+  /// registered to least recently registered until a successful result is
+  /// returned.
+  std::optional<const void *> breakCycleImpl(void *element);
+
+  /// Shared concrete implementation of the public `replace` functions.
+  template <typename T>
+  T cachedReplaceImpl(T element);
+
+  /// The set of registered cycle-breaker functions.
+  std::vector<CycleBreakerFn<Attribute>> attrCycleBreakerFns;
+  std::vector<CycleBreakerFn<Type>> typeCycleBreakerFns;
+
+  /// A cache of previously-replaced attr/types.
+  /// The key of the cache is the opaque value of an AttrOrType. Using
+  /// AttrOrType allows distinguishing between the two types when invoking
+  /// cycle-breakers. Using its opaque value avoids the cyclic dependency issue
+  /// of directly using `AttrOrType` to instantiate the cache.
+  /// The value of the cache is just the opaque value of the attr/type itself
+  /// (not the PointerUnion).
+  using AttrOrType = PointerUnion<Attribute, Type>;
+  CyclicReplacerCache<void *, const void *> cache;
 };
 
 //===----------------------------------------------------------------------===//