diff --git a/mlir/lib/Rewrite/PatternApplicator.cpp b/mlir/lib/Rewrite/PatternApplicator.cpp
--- a/mlir/lib/Rewrite/PatternApplicator.cpp
+++ b/mlir/lib/Rewrite/PatternApplicator.cpp
@@ -15,7 +15,7 @@
 #include "ByteCode.h"
 #include "llvm/Support/Debug.h"
 
-#define DEBUG_TYPE "pattern-match"
+#define DEBUG_TYPE "pattern-application"
 
 using namespace mlir;
 using namespace mlir::detail;
@@ -39,6 +39,29 @@
   });
 }
 
+// Log IR after pattern application.
+static Optional<ModuleOp> logAttemptPatternApplication(Operation *op,
+                                                       const Pattern *pattern) {
+  LLVM_DEBUG({
+    if (!op->getContext()->isMultithreadingEnabled())
+      return op->getParentOfType<ModuleOp>();
+  });
+  return llvm::None;
+}
+static void logSucessfulPatternApplication(Optional<ModuleOp> op,
+                                           const Pattern *pattern) {
+  LLVM_DEBUG({
+    llvm::dbgs() << "// *** IR Dump After Pattern Application ***\n";
+    if (op) {
+      op.getValue().dump();
+    } else {
+      llvm::dbgs()
+          << "Failed to dump module IR. Multithreading must be disabled.";
+    }
+    llvm::dbgs() << "\n\n";
+  });
+}
+
 void PatternApplicator::applyCostModel(CostModel model) {
   // Apply the cost model to the bytecode patterns first, and then the native
   // patterns.
@@ -174,18 +197,20 @@
     // benefit, so if we match we can immediately rewrite. For PDL patterns, the
     // match has already been performed, we just need to rewrite.
     rewriter.setInsertionPoint(op);
+    Optional<ModuleOp> moduleOp = logAttemptPatternApplication(op, bestPattern);
     if (pdlMatch) {
       bytecode->rewrite(rewriter, *pdlMatch, *mutableByteCodeState);
       result = success(!onSuccess || succeeded(onSuccess(*bestPattern)));
-
     } else {
       const auto *pattern = static_cast<const RewritePattern *>(bestPattern);
       result = pattern->matchAndRewrite(op, rewriter);
       if (succeeded(result) && onSuccess && failed(onSuccess(*pattern)))
         result = failure();
     }
-    if (succeeded(result))
+    if (succeeded(result)) {
+      logSucessfulPatternApplication(moduleOp, bestPattern);
       break;
+    }
 
     // Perform any necessary cleanups.
     if (onFailure)