[mlir] Allow derived rewrite patterns to define a non-virtual `initialize` hook

[rriddle]

Summary

This is a hook that allows for providing custom initialization of the pattern, e.g. if it has bounded recursion, setting the debug name, etc., without needing to define a custom constructor. A non-virtual hook was chosen to avoid polluting the vtable with code that we really just want to be inlined when constructing the pattern. The alternative to this would be to just define a constructor for each pattern, this unfortunately creates a lot of otherwise unnecessary boiler plate for a lot of patterns and a hook provides a much simpler/cleaner interface for the very common case.

Depends On D102439

[aartbik]

mlir/docs/PatternRewriter.md

145

nit: safely handles

mlir/include/mlir/IR/PatternMatch.h

283

nit: its

mlir/docs/PatternRewriter.md

 cause crashes, but create infinite loops within the application process. Given
 this, the pattern rewriting infrastructure conservatively assumes that no
 patterns have a proper bounded recursion, and will fail if recursion is
 detected. A pattern that is known to have proper support for handling recursion
 can signal this by calling `setHasBoundedRewriteRecursion` when initializing the
 pattern. This will signal to the pattern driver that recursive application of
 this pattern may happen, and the pattern is equipped to safely handle it.
 
+### Initialization
+
+Several pieces of pattern state require explicit initialization by the pattern,
+for example setting `setHasBoundedRewriteRecursion` if a pattern safely handles
+recursive application. This pattern state can be initialized either in the
+constructor of the pattern or via the utility `initialize` hook. Using the
+`initialize` hook removes the need to redefine pattern constructors just to
+inject additional pattern state initialization. An example is shown below:
+
+```c++
+class MyPattern : public RewritePattern {
+public:
+  /// Inherit the constructors from RewritePattern.
+  using RewritePattern::RewritePattern;
+
+  /// Initialize the pattern.
+  void initialize() {
+    /// Signal that this pattern safely handle recursive application.
+    setHasBoundedRewriteRecursion();
+  }
+
+  // ...
+};
+```
+
+### Construction
+
+Constructing a RewritePattern should be performed by using the static
+`RewritePattern::create<T>` utility method. This method ensures that the pattern
+is properly initialized and prepared for insertion into a `RewritePatternSet`.
+
 ## Pattern Rewriter
 
 A `PatternRewriter` is a special class that allows for a pattern to communicate
 with the driver of pattern application. As noted above, *all* IR mutations,
 including creations, are required to be performed via the `PatternRewriter`
 class. This is required because the underlying pattern driver may have state
 that would be invalidated when a mutation takes place. Examples of some of the
 more prevalent `PatternRewriter` API is shown below, please refer to the

mlir/include/mlir/IR/PatternMatch.h

virtual LogicalResult matchAndRewrite(Operation *op,
                                         PatternRewriter &rewriter) const {
     if (succeeded(match(op))) {
       rewrite(op, rewriter);
       return success();
     }
     return failure();
   }
 
+  /// This method provides a convenient interface for creating and initializing
+  /// derived rewrite patterns of the given type `T`.
+  template <typename T, typename... Args>
+  static std::unique_ptr<T> create(Args &&...args) {
+    std::unique_ptr<T> pattern =
+        std::make_unique<T>(std::forward<Args>(args)...);
+    initializePattern<T>(*pattern);
+
+    // Set a default debug name if one wasn't provided.
+    if (pattern->getDebugName().empty())
+      pattern->setDebugName(llvm::getTypeName<T>());
+    return pattern;
+  }
+
 protected:
   /// Inherit the base constructors from `Pattern`.
   using Pattern::Pattern;
 
+private:
+  /// Trait to check if T provides a `getOperationName` method.
+  template <typename T, typename... Args>
+  using has_initialize = decltype(std::declval<T>().initialize());
+  template <typename T>
+  using detect_has_initialize = llvm::is_detected<has_initialize, T>;
+
+  /// Initialize the derived pattern by calling it's initialize method.
+  template <typename T>
+  static std::enable_if_t<detect_has_initialize<T>::value>
+  initializePattern(T &pattern) {
+    pattern.initialize();
+  }
+  /// Empty derived pattern initializer for patterns that do not have an
+  /// initialize method.
+  template <typename T>
+  static std::enable_if_t<!detect_has_initialize<T>::value>
+  initializePattern(T &) {}
+
   /// An anchor for the virtual table.
   virtual void anchor();
 };
 
 namespace detail {
 /// OpOrInterfaceRewritePatternBase is a wrapper around RewritePattern that
 /// allows for matching and rewriting against an instance of a derived operation
 /// class or Interface.
public:
   }
 
 private:
   /// Add an instance of the pattern type 'T'. Return a reference to `this` for
   /// chaining insertions.
   template <typename T, typename... Args>
   std::enable_if_t<std::is_base_of<RewritePattern, T>::value>
   addImpl(Args &&... args) {
-    auto pattern = std::make_unique<T>(std::forward<Args>(args)...);
-
-    // Pattern can potentially set name in ctor. Preserve old name if present.
-    if (pattern->getDebugName().empty())
-      pattern->setDebugName(llvm::getTypeName<T>());
-
-    nativePatterns.emplace_back(std::move(pattern));
+    nativePatterns.emplace_back(
+        RewritePattern::create<T>(std::forward<Args>(args)...));
   }
   template <typename T, typename... Args>
   std::enable_if_t<std::is_base_of<PDLPatternModule, T>::value>
   addImpl(Args &&... args) {
     pdlPatterns.mergeIn(T(std::forward<Args>(args)...));
   }
 
   MLIRContext *const context;
   NativePatternListT nativePatterns;
   PDLPatternModule pdlPatterns;
 };
 
 } // end namespace mlir
 
 #endif // MLIR_PATTERN_MATCH_H

mlir/lib/Conversion/VectorToLLVM/ConvertVectorToLLVM.cpp

 //   destination subvector
 //   3. the destination subvector is inserted back in the proper place
 //   4. the op is replaced by the result of step 3.
 // The new InsertStridedSlice from step 2. will be picked up by a
 // `VectorInsertStridedSliceOpSameRankRewritePattern`.
 class VectorInsertStridedSliceOpSameRankRewritePattern
     : public OpRewritePattern<InsertStridedSliceOp> {
 public:
-  VectorInsertStridedSliceOpSameRankRewritePattern(MLIRContext *ctx)
-      : OpRewritePattern<InsertStridedSliceOp>(ctx) {
+  using OpRewritePattern<InsertStridedSliceOp>::OpRewritePattern;
+
+  void initialize() {
     // This pattern creates recursive InsertStridedSliceOp, but the recursion is
     // bounded as the rank is strictly decreasing.
     setHasBoundedRewriteRecursion();
   }
 
   LogicalResult matchAndRewrite(InsertStridedSliceOp op,
                                 PatternRewriter &rewriter) const override {
     auto srcType = op.getSourceVectorType();

 };
 
 /// Progressive lowering of ExtractStridedSliceOp to either:
 ///   1. express single offset extract as a direct shuffle.
 ///   2. extract + lower rank strided_slice + insert for the n-D case.
 class VectorExtractStridedSliceOpConversion
     : public OpRewritePattern<ExtractStridedSliceOp> {
 public:
-  VectorExtractStridedSliceOpConversion(MLIRContext *ctx)
-      : OpRewritePattern<ExtractStridedSliceOp>(ctx) {
+  using OpRewritePattern<ExtractStridedSliceOp>::OpRewritePattern;
+
+  void initialize() {
     // This pattern creates recursive ExtractStridedSliceOp, but the recursion
     // is bounded as the rank is strictly decreasing.
     setHasBoundedRewriteRecursion();
   }
 
   LogicalResult matchAndRewrite(ExtractStridedSliceOp op,
                                 PatternRewriter &rewriter) const override {
     auto dstType = op.getType();

mlir/test/lib/Dialect/Test/TestPatterns.cpp

 };
 
 //===----------------------------------------------------------------------===//
 // Recursive Rewrite Testing
 /// This pattern is applied to the same operation multiple times, but has a
 /// bounded recursion.
 struct TestBoundedRecursiveRewrite
     : public OpRewritePattern<TestRecursiveRewriteOp> {
-  TestBoundedRecursiveRewrite(MLIRContext *ctx)
-      : OpRewritePattern<TestRecursiveRewriteOp>(ctx) {
+  using OpRewritePattern<TestRecursiveRewriteOp>::OpRewritePattern;
+
+  void initialize() {
     // The conversion target handles bounding the recursion of this pattern.
     setHasBoundedRewriteRecursion();
   }
 
   LogicalResult matchAndRewrite(TestRecursiveRewriteOp op,
                                 PatternRewriter &rewriter) const final {
     // Decrement the depth of the op in-place.
     rewriter.updateRootInPlace(op, [&] {