[mlir][nfc] Remove TrivialPatternRewriters (#155248)

These are relics from the times when `PatternRewriter` was not
instantiable directly, I suppose.

Author: Hardcode84

flang/lib/Optimizer/Transforms/SimplifyRegionLite.cpp

@@ -26,22 +26,16 @@ class SimplifyRegionLitePass
 public:
   void runOnOperation() override;
 };
-
-class DummyRewriter : public mlir::PatternRewriter {
-public:
-  DummyRewriter(mlir::MLIRContext *ctx) : mlir::PatternRewriter(ctx) {}
-};
-
 } // namespace
 
 void SimplifyRegionLitePass::runOnOperation() {
   auto op = getOperation();
   auto regions = op->getRegions();
   mlir::RewritePatternSet patterns(op.getContext());
-  DummyRewriter rewriter(op.getContext());
   if (regions.empty())
     return;
 
+  mlir::PatternRewriter rewriter(op.getContext());
   (void)mlir::eraseUnreachableBlocks(rewriter, regions);
   (void)mlir::runRegionDCE(rewriter, regions);
 }

mlir/lib/Dialect/Linalg/TransformOps/LinalgTransformOps.cpp

@@ -70,12 +70,7 @@ static FailureOr<LinalgOp> tryApply(Operation *operation, Args &&...args) {
   PatternTy pattern(operation->getContext(), std::forward<Args>(args)...);
   // We want to discourage direct use of PatternRewriter in APIs but In this
   // very specific case, an IRRewriter is not enough.
-  struct TrivialPatternRewriter : public PatternRewriter {
-  public:
-    explicit TrivialPatternRewriter(MLIRContext *context)
-        : PatternRewriter(context) {}
-  };
-  TrivialPatternRewriter rewriter(operation->getContext());
+  PatternRewriter rewriter(operation->getContext());
   rewriter.setInsertionPoint(operation);
   auto result = pattern.returningMatchAndRewrite(op, rewriter);
   if (failed(result))

mlir/lib/Dialect/Transform/PDLExtension/PDLExtensionOps.cpp

@@ -100,12 +100,7 @@ LogicalResult PatternApplicatorExtension::findAllMatches(
   PatternApplicator applicator(it->second);
   // We want to discourage direct use of PatternRewriter in APIs but In this
   // very specific case, an IRRewriter is not enough.
-  struct TrivialPatternRewriter : public PatternRewriter {
-  public:
-    explicit TrivialPatternRewriter(MLIRContext *context)
-        : PatternRewriter(context) {}
-  };
-  TrivialPatternRewriter rewriter(root->getContext());
+  PatternRewriter rewriter(root->getContext());
   applicator.applyDefaultCostModel();
   root->walk([&](Operation *op) {
     if (succeeded(applicator.matchAndRewrite(op, rewriter)))

mlir/unittests/Rewrite/PatternBenefit.cpp

@@ -66,12 +66,7 @@ TEST(PatternBenefitTest, BenefitOrder) {
   PatternApplicator pa(frozenPatterns);
   pa.applyDefaultCostModel();
 
-  class MyPatternRewriter : public PatternRewriter {
-  public:
-    MyPatternRewriter(MLIRContext *ctx) : PatternRewriter(ctx) {}
-  };
-
-  MyPatternRewriter rewriter(&context);
+  PatternRewriter rewriter(&context);
   (void)pa.matchAndRewrite(*module, rewriter);
 
   EXPECT_TRUE(called1);