[mlir][IR] Add listener notifications for pattern begin/end (#84131)

This commit adds two new notifications to `RewriterBase::Listener`:
* `notifyPatternBegin`: Called when a pattern application begins during
a greedy pattern rewrite or dialect conversion.
* `notifyPatternEnd`: Called when a pattern application finishes during
a greedy pattern rewrite or dialect conversion.

The listener infrastructure already provides a `notifyMatchFailure`
callback that notifies about the reason for a pattern match failure. The
two new notifications provide additional information about pattern
applications.

This change is in preparation of improving the handle update mechanism
in the `apply_conversion_patterns` transform op.

3 files changed, 69 insertions, 23 deletions

diff --git a/mlir/include/mlir/IR/PatternMatch.h b/mlir/include/mlir/IR/PatternMatch.h
index e3500b3..49544c4 100644
--- a/mlir/include/mlir/IR/PatternMatch.h
+++ b/mlir/include/mlir/IR/PatternMatch.h
@@ -432,11 +432,22 @@ public:
     /// Note: This notification is not triggered when unlinking an operation.
     virtual void notifyOperationErased(Operation *op) {}
 
-    /// Notify the listener that the pattern failed to match the given
-    /// operation, and provide a callback to populate a diagnostic with the
-    /// reason why the failure occurred. This method allows for derived
-    /// listeners to optionally hook into the reason why a rewrite failed, and
-    /// display it to users.
+    /// Notify the listener that the specified pattern is about to be applied
+    /// at the specified root operation.
+    virtual void notifyPatternBegin(const Pattern &pattern, Operation *op) {}
+
+    /// Notify the listener that a pattern application finished with the
+    /// specified status. "success" indicates that the pattern was applied
+    /// successfully. "failure" indicates that the pattern could not be
+    /// applied. The pattern may have communicated the reason for the failure
+    /// with `notifyMatchFailure`.
+    virtual void notifyPatternEnd(const Pattern &pattern,
+                                  LogicalResult status) {}
+
+    /// Notify the listener that the pattern failed to match, and provide a
+    /// callback to populate a diagnostic with the reason why the failure
+    /// occurred. This method allows for derived listeners to optionally hook
+    /// into the reason why a rewrite failed, and display it to users.
     virtual void
     notifyMatchFailure(Location loc,
                        function_ref<void(Diagnostic &)> reasonCallback) {}
@@ -478,6 +489,15 @@ public:
       if (auto *rewriteListener = dyn_cast<RewriterBase::Listener>(listener))
         rewriteListener->notifyOperationErased(op);
     }
+    void notifyPatternBegin(const Pattern &pattern, Operation *op) override {
+      if (auto *rewriteListener = dyn_cast<RewriterBase::Listener>(listener))
+        rewriteListener->notifyPatternBegin(pattern, op);
+    }
+    void notifyPatternEnd(const Pattern &pattern,
+                          LogicalResult status) override {
+      if (auto *rewriteListener = dyn_cast<RewriterBase::Listener>(listener))
+        rewriteListener->notifyPatternEnd(pattern, status);
+    }
     void notifyMatchFailure(
         Location loc,
         function_ref<void(Diagnostic &)> reasonCallback) override {
diff --git a/mlir/lib/Transforms/Utils/DialectConversion.cpp b/mlir/lib/Transforms/Utils/DialectConversion.cpp
index c1a261e..cd49bd12 100644
--- a/mlir/lib/Transforms/Utils/DialectConversion.cpp
+++ b/mlir/lib/Transforms/Utils/DialectConversion.cpp
@@ -1856,7 +1856,8 @@ public:
   using LegalizationAction = ConversionTarget::LegalizationAction;
 
   OperationLegalizer(const ConversionTarget &targetInfo,
-                     const FrozenRewritePatternSet &patterns);
+                     const FrozenRewritePatternSet &patterns,
+                     const ConversionConfig &config);
 
   /// Returns true if the given operation is known to be illegal on the target.
   bool isIllegal(Operation *op) const;
@@ -1948,12 +1949,16 @@ private:
 
   /// The pattern applicator to use for conversions.
   PatternApplicator applicator;
+
+  /// Dialect conversion configuration.
+  const ConversionConfig &config;
 };
 } // namespace
 
 OperationLegalizer::OperationLegalizer(const ConversionTarget &targetInfo,
-                                       const FrozenRewritePatternSet &patterns)
-    : target(targetInfo), applicator(patterns) {
+                                       const FrozenRewritePatternSet &patterns,
+                                       const ConversionConfig &config)
+    : target(targetInfo), applicator(patterns), config(config) {
   // The set of patterns that can be applied to illegal operations to transform
   // them into legal ones.
   DenseMap<OperationName, LegalizationPatterns> legalizerPatterns;
@@ -2098,7 +2103,10 @@ OperationLegalizer::legalizeWithPattern(Operation *op,
 
   // Functor that returns if the given pattern may be applied.
   auto canApply = [&](const Pattern &pattern) {
-    return canApplyPattern(op, pattern, rewriter);
+    bool canApply = canApplyPattern(op, pattern, rewriter);
+    if (canApply && config.listener)
+      config.listener->notifyPatternBegin(pattern, op);
+    return canApply;
   };
 
   // Functor that cleans up the rewriter state after a pattern failed to match.
@@ -2115,6 +2123,8 @@ OperationLegalizer::legalizeWithPattern(Operation *op,
         rewriterImpl.config.notifyCallback(diag);
       }
     });
+    if (config.listener)
+      config.listener->notifyPatternEnd(pattern, failure());
     rewriterImpl.resetState(curState);
     appliedPatterns.erase(&pattern);
   };
@@ -2127,6 +2137,8 @@ OperationLegalizer::legalizeWithPattern(Operation *op,
     appliedPatterns.erase(&pattern);
     if (failed(result))
       rewriterImpl.resetState(curState);
+    if (config.listener)
+      config.listener->notifyPatternEnd(pattern, result);
     return result;
   };
 
@@ -2502,7 +2514,8 @@ struct OperationConverter {
                               const FrozenRewritePatternSet &patterns,
                               const ConversionConfig &config,
                               OpConversionMode mode)
-      : opLegalizer(target, patterns), config(config), mode(mode) {}
+      : config(config), opLegalizer(target, patterns, this->config),
+        mode(mode) {}
 
   /// Converts the given operations to the conversion target.
   LogicalResult convertOperations(ArrayRef<Operation *> ops);
@@ -2539,12 +2552,12 @@ private:
       ConversionPatternRewriterImpl &rewriterImpl,
       const DenseMap<Value, SmallVector<Value>> &inverseMapping);
 
-  /// The legalizer to use when converting operations.
-  OperationLegalizer opLegalizer;
-
   /// Dialect conversion configuration.
   ConversionConfig config;
 
+  /// The legalizer to use when converting operations.
+  OperationLegalizer opLegalizer;
+
   /// The conversion mode to use when legalizing operations.
   OpConversionMode mode;
 };
diff --git a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
index 51d2f5e..6cb5635 100644
--- a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
+++ b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
@@ -562,8 +562,7 @@ bool GreedyPatternRewriteDriver::processWorklist() {
     // Try to match one of the patterns. The rewriter is automatically
     // notified of any necessary changes, so there is nothing else to do
     // here.
-#ifndef NDEBUG
-    auto canApply = [&](const Pattern &pattern) {
+    auto canApplyCallback = [&](const Pattern &pattern) {
       LLVM_DEBUG({
         logger.getOStream() << "\n";
         logger.startLine() << "* Pattern " << pattern.getDebugName() << " : '"
@@ -572,20 +571,34 @@ bool GreedyPatternRewriteDriver::processWorklist() {
         logger.getOStream() << ")' {\n";
         logger.indent();
       });
+      if (config.listener)
+        config.listener->notifyPatternBegin(pattern, op);
       return true;
     };
-    auto onFailure = [&](const Pattern &pattern) {
+    function_ref<bool(const Pattern &)> canApply = canApplyCallback;
+    auto onFailureCallback = [&](const Pattern &pattern) {
       LLVM_DEBUG(logResult("failure", "pattern failed to match"));
+      if (config.listener)
+        config.listener->notifyPatternEnd(pattern, failure());
     };
-    auto onSuccess = [&](const Pattern &pattern) {
+    function_ref<void(const Pattern &)> onFailure = onFailureCallback;
+    auto onSuccessCallback = [&](const Pattern &pattern) {
       LLVM_DEBUG(logResult("success", "pattern applied successfully"));
+      if (config.listener)
+        config.listener->notifyPatternEnd(pattern, success());
       return success();
     };
-#else
-    function_ref<bool(const Pattern &)> canApply = {};
-    function_ref<void(const Pattern &)> onFailure = {};
-    function_ref<LogicalResult(const Pattern &)> onSuccess = {};
-#endif
+    function_ref<LogicalResult(const Pattern &)> onSuccess = onSuccessCallback;
+
+#ifdef NDEBUG
+    // Optimization: PatternApplicator callbacks are not needed when running in
+    // optimized mode and without a listener.
+    if (!config.listener) {
+      canApply = nullptr;
+      onFailure = nullptr;
+      onSuccess = nullptr;
+    }
+#endif // NDEBUG
 
 #if MLIR_ENABLE_EXPENSIVE_PATTERN_API_CHECKS
     if (config.scope) {
@@ -731,7 +744,7 @@ void GreedyPatternRewriteDriver::notifyMatchFailure(
   LLVM_DEBUG({
     Diagnostic diag(loc, DiagnosticSeverity::Remark);
     reasonCallback(diag);
-    logger.startLine() << "** Failure : " << diag.str() << "\n";
+    logger.startLine() << "** Match Failure : " << diag.str() << "\n";
   });
   if (config.listener)
     config.listener->notifyMatchFailure(loc, reasonCallback);