diff --git a/mlir/lib/Transforms/Canonicalizer.cpp b/mlir/lib/Transforms/Canonicalizer.cpp
--- a/mlir/lib/Transforms/Canonicalizer.cpp
+++ b/mlir/lib/Transforms/Canonicalizer.cpp
@@ -21,22 +21,17 @@
 namespace {
 /// Canonicalize operations in nested regions.
 struct Canonicalizer : public CanonicalizerBase<Canonicalizer> {
+  Canonicalizer() = default;
   Canonicalizer(const GreedyRewriteConfig &config,
                 ArrayRef<std::string> disabledPatterns,
-                ArrayRef<std::string> enabledPatterns)
-      : config(config) {
+                ArrayRef<std::string> enabledPatterns) {
+    this->topDownProcessingEnabled = config.useTopDownTraversal;
+    this->enableRegionSimplification = config.enableRegionSimplification;
+    this->maxIterations = config.maxIterations;
     this->disabledPatterns = disabledPatterns;
     this->enabledPatterns = enabledPatterns;
   }
 
-  Canonicalizer() {
-    // Default constructed Canonicalizer takes its settings from command line
-    // options.
-    config.useTopDownTraversal = topDownProcessingEnabled;
-    config.enableRegionSimplification = enableRegionSimplification;
-    config.maxIterations = maxIterations;
-  }
-
   /// Initialize the canonicalizer by building the set of patterns used during
   /// execution.
   LogicalResult initialize(MLIRContext *context) override {
@@ -51,11 +46,13 @@
     return success();
   }
   void runOnOperation() override {
-    (void)applyPatternsAndFoldGreedily(getOperation()->getRegions(), patterns,
-                                       config);
+    GreedyRewriteConfig config;
+    config.useTopDownTraversal = topDownProcessingEnabled;
+    config.enableRegionSimplification = enableRegionSimplification;
+    config.maxIterations = maxIterations;
+    (void)applyPatternsAndFoldGreedily(getOperation(), patterns, config);
   }
 
-  GreedyRewriteConfig config;
   FrozenRewritePatternSet patterns;
 };
 } // namespace
diff --git a/mlir/test/Transforms/test-canonicalize.mlir b/mlir/test/Transforms/test-canonicalize.mlir
--- a/mlir/test/Transforms/test-canonicalize.mlir
+++ b/mlir/test/Transforms/test-canonicalize.mlir
@@ -1,4 +1,5 @@
 // RUN: mlir-opt %s -pass-pipeline='func.func(canonicalize)' | FileCheck %s
+// RUN: mlir-opt %s -pass-pipeline='func.func(canonicalize{region-simplify=false})' | FileCheck %s --check-prefixes=CHECK,NO-RS
 
 // CHECK-LABEL: func @remove_op_with_inner_ops_pattern
 func.func @remove_op_with_inner_ops_pattern() {
@@ -89,3 +90,15 @@
   // CHECK: return %[[CST]]
   return %0 : i32
 }
+
+// Check that the option to control region simplification actually works
+// CHECK-LABEL: test_region_simplify
+func.func @test_region_simplify() {
+  // CHECK-NEXT:   return
+  // NO-RS-NEXT: ^bb1
+  // NO-RS-NEXT:   return
+  // CHECK-NEXT: }
+  return
+^bb1:
+  return
+}