diff --git a/mlir/include/mlir/Tools/PDLL/AST/Nodes.h b/mlir/include/mlir/Tools/PDLL/AST/Nodes.h
--- a/mlir/include/mlir/Tools/PDLL/AST/Nodes.h
+++ b/mlir/include/mlir/Tools/PDLL/AST/Nodes.h
@@ -1239,8 +1239,8 @@
 }
 
 inline bool Expr::classof(const Node *node) {
-  return isa<AttributeExpr, DeclRefExpr, MemberAccessExpr, OperationExpr,
-             TupleExpr, TypeExpr>(node);
+  return isa<AttributeExpr, CallExpr, DeclRefExpr, MemberAccessExpr,
+             OperationExpr, TupleExpr, TypeExpr>(node);
 }
 
 inline bool OpRewriteStmt::classof(const Node *node) {
diff --git a/mlir/include/mlir/Tools/PDLL/CodeGen/MLIRGen.h b/mlir/include/mlir/Tools/PDLL/CodeGen/MLIRGen.h
new file mode 100644
--- /dev/null
+++ b/mlir/include/mlir/Tools/PDLL/CodeGen/MLIRGen.h
@@ -0,0 +1,41 @@
+//===- MLIRGen.h - MLIR PDLL Code Generation --------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_TOOLS_PDLL_CODEGEN_MLIRGEN_H_
+#define MLIR_TOOLS_PDLL_CODEGEN_MLIRGEN_H_
+
+#include <memory>
+
+#include "mlir/Support/LogicalResult.h"
+
+namespace llvm {
+class SourceMgr;
+} // namespace llvm
+
+namespace mlir {
+class MLIRContext;
+class ModuleOp;
+template <typename OpT>
+class OwningOpRef;
+
+namespace pdll {
+namespace ast {
+class Context;
+class Module;
+} // namespace ast
+
+/// Given a PDLL module, generate an MLIR PDL pattern module within the given
+/// MLIR context.
+OwningOpRef<ModuleOp> codegenPDLLToMLIR(MLIRContext *mlirContext,
+                                        const ast::Context &context,
+                                        const llvm::SourceMgr &sourceMgr,
+                                        const ast::Module &module);
+} // namespace pdll
+} // namespace mlir
+
+#endif // MLIR_TOOLS_PDLL_CODEGEN_MLIRGEN_H_
diff --git a/mlir/lib/Tools/PDLL/CMakeLists.txt b/mlir/lib/Tools/PDLL/CMakeLists.txt
--- a/mlir/lib/Tools/PDLL/CMakeLists.txt
+++ b/mlir/lib/Tools/PDLL/CMakeLists.txt
@@ -1,2 +1,3 @@
 add_subdirectory(AST)
+add_subdirectory(CodeGen)
 add_subdirectory(Parser)
diff --git a/mlir/lib/Tools/PDLL/CodeGen/CMakeLists.txt b/mlir/lib/Tools/PDLL/CodeGen/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Tools/PDLL/CodeGen/CMakeLists.txt
@@ -0,0 +1,9 @@
+add_mlir_library(MLIRPDLLCodeGen
+  MLIRGen.cpp
+
+  LINK_LIBS PUBLIC
+  MLIRParser
+  MLIRPDLLAST
+  MLIRPDL
+  MLIRSupport
+  )
diff --git a/mlir/lib/Tools/PDLL/CodeGen/MLIRGen.cpp b/mlir/lib/Tools/PDLL/CodeGen/MLIRGen.cpp
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Tools/PDLL/CodeGen/MLIRGen.cpp
@@ -0,0 +1,580 @@
+//===- MLIRGen.cpp --------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Tools/PDLL/CodeGen/MLIRGen.h"
+#include "mlir/Dialect/PDL/IR/PDL.h"
+#include "mlir/Dialect/PDL/IR/PDLOps.h"
+#include "mlir/Dialect/PDL/IR/PDLTypes.h"
+#include "mlir/IR/Builders.h"
+#include "mlir/IR/BuiltinOps.h"
+#include "mlir/IR/Verifier.h"
+#include "mlir/Parser.h"
+#include "mlir/Tools/PDLL/AST/Context.h"
+#include "mlir/Tools/PDLL/AST/Nodes.h"
+#include "mlir/Tools/PDLL/AST/Types.h"
+#include "llvm/ADT/ScopedHashTable.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/TypeSwitch.h"
+
+using namespace mlir;
+using namespace mlir::pdll;
+
+//===----------------------------------------------------------------------===//
+// CodeGen
+//===----------------------------------------------------------------------===//
+
+namespace {
+class CodeGen {
+public:
+  CodeGen(MLIRContext *mlirContext, const ast::Context &context,
+          const llvm::SourceMgr &sourceMgr)
+      : builder(mlirContext), sourceMgr(sourceMgr) {
+    // Make sure that the PDL dialect is loaded.
+    mlirContext->loadDialect<pdl::PDLDialect>();
+  }
+
+  OwningOpRef<ModuleOp> generate(const ast::Module &module);
+
+private:
+  /// Generate an MLIR location from the given source location.
+  Location genLoc(llvm::SMLoc loc);
+  Location genLoc(llvm::SMRange loc) { return genLoc(loc.Start); }
+
+  /// Generate an MLIR type from the given source type.
+  Type genType(ast::Type type);
+
+  /// Generate MLIR for the given AST node.
+  void gen(const ast::Node *node);
+
+  //===--------------------------------------------------------------------===//
+  // Statements
+  //===--------------------------------------------------------------------===//
+
+  void genImpl(const ast::CompoundStmt *stmt);
+  void genImpl(const ast::LetStmt *stmt);
+  void genImpl(const ast::EraseStmt *stmt);
+  void genImpl(const ast::ReplaceStmt *stmt);
+  void genImpl(const ast::RewriteStmt *stmt);
+  void genImpl(const ast::ReturnStmt *stmt);
+
+  //===--------------------------------------------------------------------===//
+  // Decls
+  //===--------------------------------------------------------------------===//
+
+  void genImpl(const ast::UserConstraintDecl *decl);
+  void genImpl(const ast::UserRewriteDecl *decl);
+  void genImpl(const ast::PatternDecl *decl);
+  SmallVector<Value> genVar(const ast::VariableDecl *varDecl);
+
+  /// Generate the value for a variable that does not have an initializer
+  /// expression, i.e. create the PDL value based on the type/constraints of the
+  /// variable.
+  Value genNonInitializerVar(const ast::VariableDecl *varDecl, Location loc);
+
+  /// Apply the constraints of the given variable to `values`, which correspond
+  /// to the MLIR values of the variable.
+  void applyVarConstraints(const ast::VariableDecl *varDecl, ValueRange values);
+
+  //===--------------------------------------------------------------------===//
+  // Expressions
+  //===--------------------------------------------------------------------===//
+
+  Value genSingleExpr(const ast::Expr *expr);
+  SmallVector<Value> genExpr(const ast::Expr *expr);
+  Value genExprImpl(const ast::AttributeExpr *expr);
+  SmallVector<Value> genExprImpl(const ast::CallExpr *expr);
+  SmallVector<Value> genExprImpl(const ast::DeclRefExpr *expr);
+  Value genExprImpl(const ast::MemberAccessExpr *expr);
+  Value genExprImpl(const ast::OperationExpr *expr);
+  SmallVector<Value> genExprImpl(const ast::TupleExpr *expr);
+  Value genExprImpl(const ast::TypeExpr *expr);
+
+  SmallVector<Value> genConstraintCall(const ast::UserConstraintDecl *decl,
+                                       Location loc, ValueRange inputs);
+  SmallVector<Value> genRewriteCall(const ast::UserRewriteDecl *decl,
+                                    Location loc, ValueRange inputs);
+  template <typename PDLOpT, typename T>
+  SmallVector<Value> genConstraintOrRewriteCall(const T *decl, Location loc,
+                                                ValueRange inputs);
+
+  //===--------------------------------------------------------------------===//
+  // Fields
+  //===--------------------------------------------------------------------===//
+
+  /// The MLIR builder used for building the resultant IR.
+  OpBuilder builder;
+
+  /// A map from variable declarations to the mlir equivalent.
+  using VariableMapTy =
+      llvm::ScopedHashTable<const ast::VariableDecl *, SmallVector<Value>>;
+  VariableMapTy variables;
+
+  /// The source manager of the PDLL ast.
+  const llvm::SourceMgr &sourceMgr;
+};
+} // namespace
+
+OwningOpRef<ModuleOp> CodeGen::generate(const ast::Module &module) {
+  OwningOpRef<ModuleOp> mlirModule =
+      builder.create<ModuleOp>(genLoc(module.getLoc()));
+  builder.setInsertionPointToStart(mlirModule->getBody());
+
+  // Generate code for each of the decls within the module.
+  for (const ast::Decl *decl : module.getChildren())
+    gen(decl);
+
+  return mlirModule;
+}
+
+Location CodeGen::genLoc(llvm::SMLoc loc) {
+  unsigned fileID = sourceMgr.FindBufferContainingLoc(loc);
+
+  // TODO: Fix performance issues in SourceMgr::getLineAndColumn so that we can
+  //       use it here.
+  auto &bufferInfo = sourceMgr.getBufferInfo(fileID);
+  unsigned lineNo = bufferInfo.getLineNumber(loc.getPointer());
+  unsigned column =
+      (loc.getPointer() - bufferInfo.getPointerForLineNumber(lineNo)) + 1;
+  auto *buffer = sourceMgr.getMemoryBuffer(fileID);
+
+  return FileLineColLoc::get(builder.getContext(),
+                             buffer->getBufferIdentifier(), lineNo, column);
+}
+
+Type CodeGen::genType(ast::Type type) {
+  return TypeSwitch<ast::Type, Type>(type)
+      .Case([&](ast::AttributeType astType) -> Type {
+        return builder.getType<pdl::AttributeType>();
+      })
+      .Case([&](ast::OperationType astType) -> Type {
+        return builder.getType<pdl::OperationType>();
+      })
+      .Case([&](ast::TypeType astType) -> Type {
+        return builder.getType<pdl::TypeType>();
+      })
+      .Case([&](ast::ValueType astType) -> Type {
+        return builder.getType<pdl::ValueType>();
+      })
+      .Case([&](ast::RangeType astType) -> Type {
+        return pdl::RangeType::get(genType(astType.getElementType()));
+      });
+}
+
+void CodeGen::gen(const ast::Node *node) {
+  TypeSwitch<const ast::Node *>(node)
+      .Case<const ast::CompoundStmt, const ast::LetStmt, const ast::EraseStmt,
+            const ast::ReplaceStmt, const ast::RewriteStmt,
+            const ast::ReturnStmt, const ast::UserConstraintDecl,
+            const ast::UserRewriteDecl, const ast::PatternDecl>(
+          [&](auto derivedNode) { this->genImpl(derivedNode); })
+      .Case([&](const ast::Expr *expr) { genExpr(expr); });
+}
+
+//===----------------------------------------------------------------------===//
+// CodeGen: Statements
+//===----------------------------------------------------------------------===//
+
+void CodeGen::genImpl(const ast::CompoundStmt *stmt) {
+  VariableMapTy::ScopeTy varScope(variables);
+  for (const ast::Stmt *childStmt : stmt->getChildren())
+    gen(childStmt);
+}
+
+void CodeGen::genImpl(const ast::LetStmt *stmt) { genVar(stmt->getVarDecl()); }
+
+/// If the given builder is nested under a PDL PatternOp, build a rewrite
+/// operation and update the builder to nest under it. This is necessary for
+/// PDLL operation rewrite statements that are directly nested within a Pattern.
+static void checkAndNestUnderRewriteOp(OpBuilder &builder, Value rootExpr,
+                                       Location loc) {
+  if (isa<pdl::PatternOp>(builder.getInsertionBlock()->getParentOp())) {
+    pdl::RewriteOp rewrite = builder.create<pdl::RewriteOp>(
+        loc, rootExpr, /*name=*/StringAttr(),
+        /*externalArgs=*/ValueRange(), /*externalConstParams=*/ArrayAttr());
+    builder.createBlock(&rewrite.body());
+  }
+}
+
+void CodeGen::genImpl(const ast::EraseStmt *stmt) {
+  OpBuilder::InsertionGuard insertGuard(builder);
+  Value rootExpr = genSingleExpr(stmt->getRootOpExpr());
+  Location loc = genLoc(stmt->getLoc());
+
+  // Make sure we are nested in a RewriteOp.
+  checkAndNestUnderRewriteOp(builder, rootExpr, loc);
+  builder.create<pdl::EraseOp>(loc, rootExpr);
+}
+
+void CodeGen::genImpl(const ast::ReplaceStmt *stmt) {
+  OpBuilder::InsertionGuard insertGuard(builder);
+  Value rootExpr = genSingleExpr(stmt->getRootOpExpr());
+  Location loc = genLoc(stmt->getLoc());
+
+  // Make sure we are nested in a RewriteOp.
+  checkAndNestUnderRewriteOp(builder, rootExpr, loc);
+
+  SmallVector<Value> replValues;
+  for (ast::Expr *replExpr : stmt->getReplExprs())
+    replValues.push_back(genSingleExpr(replExpr));
+
+  // Check to see if the statement has a replacement operation, or a range of
+  // replacement values.
+  bool usesReplOperation =
+      replValues.size() == 1 &&
+      replValues.front().getType().isa<pdl::OperationType>();
+  builder.create<pdl::ReplaceOp>(
+      loc, rootExpr, usesReplOperation ? replValues[0] : Value(),
+      usesReplOperation ? ValueRange() : ValueRange(replValues));
+}
+
+void CodeGen::genImpl(const ast::RewriteStmt *stmt) {
+  OpBuilder::InsertionGuard insertGuard(builder);
+  Value rootExpr = genSingleExpr(stmt->getRootOpExpr());
+
+  // Make sure we are nested in a RewriteOp.
+  checkAndNestUnderRewriteOp(builder, rootExpr, genLoc(stmt->getLoc()));
+  gen(stmt->getRewriteBody());
+}
+
+void CodeGen::genImpl(const ast::ReturnStmt *stmt) {
+  // ReturnStmt generation is handled by the respective constraint or rewrite
+  // parent node.
+}
+
+//===----------------------------------------------------------------------===//
+// CodeGen: Decls
+//===----------------------------------------------------------------------===//
+
+void CodeGen::genImpl(const ast::UserConstraintDecl *decl) {
+  // All PDLL constraints get inlined when called, and the main native
+  // constraint declarations doesn't require any MLIR to be generated, only uses
+  // of it do.
+}
+
+void CodeGen::genImpl(const ast::UserRewriteDecl *decl) {
+  // All PDLL rewrites get inlined when called, and the main native
+  // rewrite declarations doesn't require any MLIR to be generated, only uses
+  // of it do.
+}
+
+void CodeGen::genImpl(const ast::PatternDecl *decl) {
+  const ast::Name *name = decl->getName();
+
+  // FIXME: Properly model HasBoundedRecursion in PDL so that we don't drop it
+  // here.
+  pdl::PatternOp pattern = builder.create<pdl::PatternOp>(
+      genLoc(decl->getLoc()), decl->getBenefit(),
+      name ? Optional<StringRef>(name->getName()) : Optional<StringRef>());
+
+  OpBuilder::InsertionGuard savedInsertPoint(builder);
+  builder.setInsertionPointToStart(pattern.getBody());
+  gen(decl->getBody());
+}
+
+SmallVector<Value> CodeGen::genVar(const ast::VariableDecl *varDecl) {
+  if (variables.count(varDecl))
+    return variables.lookup(varDecl);
+  Location loc = genLoc(varDecl->getLoc());
+
+  // If the variable has an initial value, use that as the base value.
+  // Otherwise, generate a value using the constraint list.
+  SmallVector<Value> values;
+  if (const ast::Expr *initExpr = varDecl->getInitExpr())
+    values = genExpr(initExpr);
+  else
+    values.push_back(genNonInitializerVar(varDecl, loc));
+
+  // Apply the constraints of the values of the variable.
+  applyVarConstraints(varDecl, values);
+
+  variables.insert(varDecl, values);
+  return values;
+}
+
+Value CodeGen::genNonInitializerVar(const ast::VariableDecl *varDecl,
+                                    Location loc) {
+  // A functor used to generate expressions nested
+  auto getTypeConstraint = [&]() -> Value {
+    for (const ast::ConstraintRef &constraint : varDecl->getConstraints()) {
+      Value typeValue =
+          TypeSwitch<const ast::Node *, Value>(constraint.constraint)
+              .Case<ast::AttrConstraintDecl, ast::ValueConstraintDecl,
+                    ast::ValueRangeConstraintDecl>([&](auto *cst) -> Value {
+                if (auto *typeConstraintExpr = cst->getTypeExpr())
+                  return genSingleExpr(typeConstraintExpr);
+                return Value();
+              })
+              .Default(Value());
+      if (typeValue)
+        return typeValue;
+    }
+    return Value();
+  };
+
+  // Generate a value based on the type of the variable.
+  ast::Type type = varDecl->getType();
+  Type mlirType = genType(type);
+  if (type.isa<ast::ValueType>())
+    return builder.create<pdl::OperandOp>(loc, mlirType, getTypeConstraint());
+  if (type.isa<ast::TypeType>())
+    return builder.create<pdl::TypeOp>(loc, mlirType, /*type=*/TypeAttr());
+  if (type.isa<ast::AttributeType>())
+    return builder.create<pdl::AttributeOp>(loc, getTypeConstraint());
+  if (ast::OperationType opType = type.dyn_cast<ast::OperationType>()) {
+    Value operands = builder.create<pdl::OperandsOp>(
+        loc, pdl::RangeType::get(builder.getType<pdl::ValueType>()),
+        /*type=*/Value());
+    Value results = builder.create<pdl::TypesOp>(
+        loc, pdl::RangeType::get(builder.getType<pdl::TypeType>()),
+        /*types=*/ArrayAttr());
+    return builder.create<pdl::OperationOp>(loc, opType.getName(), operands,
+                                            llvm::None, ValueRange(), results);
+  }
+
+  if (ast::RangeType rangeTy = type.dyn_cast<ast::RangeType>()) {
+    ast::Type eleTy = rangeTy.getElementType();
+    if (eleTy.isa<ast::ValueType>())
+      return builder.create<pdl::OperandsOp>(loc, mlirType,
+                                             getTypeConstraint());
+    if (eleTy.isa<ast::TypeType>())
+      return builder.create<pdl::TypesOp>(loc, mlirType, /*types=*/ArrayAttr());
+  }
+
+  llvm_unreachable("invalid non-initialized variable type");
+}
+
+void CodeGen::applyVarConstraints(const ast::VariableDecl *varDecl,
+                                  ValueRange values) {
+  // Generate calls to any user constraints that were attached via the
+  // constraint list.
+  for (const ast::ConstraintRef &ref : varDecl->getConstraints())
+    if (const auto *userCst = dyn_cast<ast::UserConstraintDecl>(ref.constraint))
+      genConstraintCall(userCst, genLoc(ref.referenceLoc), values);
+}
+
+//===----------------------------------------------------------------------===//
+// CodeGen: Expressions
+//===----------------------------------------------------------------------===//
+
+Value CodeGen::genSingleExpr(const ast::Expr *expr) {
+  return TypeSwitch<const ast::Expr *, Value>(expr)
+      .Case<const ast::AttributeExpr, const ast::MemberAccessExpr,
+            const ast::OperationExpr, const ast::TypeExpr>(
+          [&](auto derivedNode) { return this->genExprImpl(derivedNode); })
+      .Case<const ast::CallExpr, const ast::DeclRefExpr, const ast::TupleExpr>(
+          [&](auto derivedNode) {
+            SmallVector<Value> results = this->genExprImpl(derivedNode);
+            assert(results.size() == 1 && "expected single expression result");
+            return results[0];
+          });
+}
+
+SmallVector<Value> CodeGen::genExpr(const ast::Expr *expr) {
+  return TypeSwitch<const ast::Expr *, SmallVector<Value>>(expr)
+      .Case<const ast::CallExpr, const ast::DeclRefExpr, const ast::TupleExpr>(
+          [&](auto derivedNode) { return this->genExprImpl(derivedNode); })
+      .Default([&](const ast::Expr *expr) -> SmallVector<Value> {
+        return {genSingleExpr(expr)};
+      });
+}
+
+Value CodeGen::genExprImpl(const ast::AttributeExpr *expr) {
+  Attribute attr = parseAttribute(expr->getValue(), builder.getContext());
+  assert(attr && "invalid mlir attribute data");
+  return builder.create<pdl::AttributeOp>(genLoc(expr->getLoc()), attr);
+}
+
+SmallVector<Value> CodeGen::genExprImpl(const ast::CallExpr *expr) {
+  Location loc = genLoc(expr->getLoc());
+  SmallVector<Value> arguments;
+  for (const ast::Expr *arg : expr->getArguments())
+    arguments.push_back(genSingleExpr(arg));
+
+  // Resolve the callable expression of this call.
+  auto *callableExpr = dyn_cast<ast::DeclRefExpr>(expr->getCallableExpr());
+  assert(callableExpr && "unhandled CallExpr callable");
+
+  // Generate the PDL based on the type of callable.
+  const ast::Decl *callable = callableExpr->getDecl();
+  if (const auto *decl = dyn_cast<ast::UserConstraintDecl>(callable))
+    return genConstraintCall(decl, loc, arguments);
+  if (const auto *decl = dyn_cast<ast::UserRewriteDecl>(callable))
+    return genRewriteCall(decl, loc, arguments);
+  llvm_unreachable("unhandled CallExpr callable");
+}
+
+SmallVector<Value> CodeGen::genExprImpl(const ast::DeclRefExpr *expr) {
+  if (const auto *varDecl = dyn_cast<ast::VariableDecl>(expr->getDecl()))
+    return genVar(varDecl);
+  llvm_unreachable("unknown decl reference expression");
+}
+
+Value CodeGen::genExprImpl(const ast::MemberAccessExpr *expr) {
+  Location loc = genLoc(expr->getLoc());
+  StringRef name = expr->getMemberName();
+  SmallVector<Value> parentExprs = genExpr(expr->getParentExpr());
+  ast::Type parentType = expr->getParentExpr()->getType();
+
+  // Handle operation based member access.
+  if (ast::OperationType opType = parentType.dyn_cast<ast::OperationType>()) {
+    if (isa<ast::AllResultsMemberAccessExpr>(expr)) {
+      Type mlirType = genType(expr->getType());
+      if (mlirType.isa<pdl::ValueType>())
+        return builder.create<pdl::ResultOp>(loc, mlirType, parentExprs[0],
+                                             builder.getI32IntegerAttr(0));
+      return builder.create<pdl::ResultsOp>(loc, mlirType, parentExprs[0]);
+    }
+    llvm_unreachable("unhandled operation member access expression");
+  }
+
+  // Handle tuple based member access.
+  if (auto tupleType = parentType.dyn_cast<ast::TupleType>()) {
+    auto elementNames = tupleType.getElementNames();
+
+    // The index is either a numeric index, or a name.
+    unsigned index = 0;
+    if (llvm::isDigit(name[0]))
+      name.getAsInteger(/*Radix=*/10, index);
+    else
+      index = llvm::find(elementNames, name) - elementNames.begin();
+
+    assert(index < parentExprs.size() && "invalid result index");
+    return parentExprs[index];
+  }
+
+  llvm_unreachable("unhandled member access expression");
+}
+
+Value CodeGen::genExprImpl(const ast::OperationExpr *expr) {
+  Location loc = genLoc(expr->getLoc());
+  Optional<StringRef> opName = expr->getName();
+
+  // Operands.
+  SmallVector<Value> operands;
+  for (const ast::Expr *operand : expr->getOperands())
+    operands.push_back(genSingleExpr(operand));
+
+  // Attributes.
+  SmallVector<StringRef> attrNames;
+  SmallVector<Value> attrValues;
+  for (const ast::NamedAttributeDecl *attr : expr->getAttributes()) {
+    attrNames.push_back(attr->getName().getName());
+    attrValues.push_back(genSingleExpr(attr->getValue()));
+  }
+
+  // Results.
+  SmallVector<Value> results;
+  for (const ast::Expr *result : expr->getResultTypes())
+    results.push_back(genSingleExpr(result));
+
+  return builder.create<pdl::OperationOp>(loc, opName, operands, attrNames,
+                                          attrValues, results);
+}
+
+SmallVector<Value> CodeGen::genExprImpl(const ast::TupleExpr *expr) {
+  SmallVector<Value> elements;
+  for (const ast::Expr *element : expr->getElements())
+    elements.push_back(genSingleExpr(element));
+  return elements;
+}
+
+Value CodeGen::genExprImpl(const ast::TypeExpr *expr) {
+  Type type = parseType(expr->getValue(), builder.getContext());
+  assert(type && "invalid mlir type data");
+  return builder.create<pdl::TypeOp>(genLoc(expr->getLoc()),
+                                     builder.getType<pdl::TypeType>(),
+                                     TypeAttr::get(type));
+}
+
+SmallVector<Value>
+CodeGen::genConstraintCall(const ast::UserConstraintDecl *decl, Location loc,
+                           ValueRange inputs) {
+  // Apply any constraints defined on the arguments to the input values.
+  for (auto it : llvm::zip(decl->getInputs(), inputs))
+    applyVarConstraints(std::get<0>(it), std::get<1>(it));
+
+  // Generate the constraint call.
+  SmallVector<Value> results =
+      genConstraintOrRewriteCall<pdl::ApplyNativeConstraintOp>(decl, loc,
+                                                               inputs);
+
+  // Apply any constraints defined on the results of the constraint.
+  for (auto it : llvm::zip(decl->getResults(), results))
+    applyVarConstraints(std::get<0>(it), std::get<1>(it));
+  return results;
+}
+
+SmallVector<Value> CodeGen::genRewriteCall(const ast::UserRewriteDecl *decl,
+                                           Location loc, ValueRange inputs) {
+  return genConstraintOrRewriteCall<pdl::ApplyNativeRewriteOp>(decl, loc,
+                                                               inputs);
+}
+
+template <typename PDLOpT, typename T>
+SmallVector<Value> CodeGen::genConstraintOrRewriteCall(const T *decl,
+                                                       Location loc,
+                                                       ValueRange inputs) {
+  const ast::CompoundStmt *cstBody = decl->getBody();
+
+  // If the decl doesn't have a statement body, it is a native decl.
+  if (!cstBody) {
+    ast::Type declResultType = decl->getResultType();
+    SmallVector<Type> resultTypes;
+    if (ast::TupleType tupleType = declResultType.dyn_cast<ast::TupleType>()) {
+      for (ast::Type type : tupleType.getElementTypes())
+        resultTypes.push_back(genType(type));
+    } else {
+      resultTypes.push_back(genType(declResultType));
+    }
+
+    // FIXME: We currently do not have a modeling for the "constant params"
+    // support PDL provides. We should either figure out a modeling for this, or
+    // refactor the support within PDL to be something a bit more reasonable for
+    // what we need as a frontend.
+    Operation *pdlOp = builder.create<PDLOpT>(loc, resultTypes,
+                                              decl->getName().getName(), inputs,
+                                              /*params=*/ArrayAttr());
+    return pdlOp->getResults();
+  }
+
+  // Otherwise, this is a PDLL decl.
+  VariableMapTy::ScopeTy varScope(variables);
+
+  // Map the inputs of the call to the decl arguments.
+  // Note: This is only valid because we do not support recursion, meaning
+  // we don't need to worry about conflicting mappings here.
+  for (auto it : llvm::zip(inputs, decl->getInputs()))
+    variables.insert(std::get<1>(it), {std::get<0>(it)});
+
+  // Visit the body of the call as normal.
+  gen(cstBody);
+
+  // If the decl has no results, there is nothing to do.
+  if (cstBody->getChildren().empty())
+    return SmallVector<Value>();
+  auto *returnStmt = dyn_cast<ast::ReturnStmt>(cstBody->getChildren().back());
+  if (!returnStmt)
+    return SmallVector<Value>();
+
+  // Otherwise, grab the results from the return statement.
+  return genExpr(returnStmt->getResultExpr());
+}
+
+//===----------------------------------------------------------------------===//
+// MLIRGen
+//===----------------------------------------------------------------------===//
+
+OwningOpRef<ModuleOp> mlir::pdll::codegenPDLLToMLIR(
+    MLIRContext *mlirContext, const ast::Context &context,
+    const llvm::SourceMgr &sourceMgr, const ast::Module &module) {
+  CodeGen codegen(mlirContext, context, sourceMgr);
+  OwningOpRef<ModuleOp> mlirModule = codegen.generate(module);
+  if (failed(verify(*mlirModule)))
+    return nullptr;
+  return mlirModule;
+}
diff --git a/mlir/test/mlir-pdll/CodeGen/MLIR/decl.pdll b/mlir/test/mlir-pdll/CodeGen/MLIR/decl.pdll
new file mode 100644
--- /dev/null
+++ b/mlir/test/mlir-pdll/CodeGen/MLIR/decl.pdll
@@ -0,0 +1,97 @@
+// RUN: mlir-pdll %s -I %S -split-input-file -x mlir | FileCheck %s
+
+//===----------------------------------------------------------------------===//
+// PatternDecl
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern : benefit(0) {
+Pattern => erase _: Op;
+
+// -----
+
+// CHECK: pdl.pattern @NamedPattern : benefit(0) {
+Pattern NamedPattern => erase _: Op;
+
+// -----
+
+// CHECK: pdl.pattern @NamedPattern : benefit(10) {
+Pattern NamedPattern with benefit(10), recursion => erase _: Op;
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// VariableDecl
+//===----------------------------------------------------------------------===//
+
+// Test the case of a variable with an initializer.
+
+// CHECK: pdl.pattern @VarWithInit
+// CHECK: %[[INIT:.*]] = operation "test.op"
+// CHECK: rewrite %[[INIT]] {
+// CHECK:   erase %[[INIT]]
+Pattern VarWithInit {
+  let var = op<test.op>;
+  erase var;
+}
+
+// -----
+
+// Test range based constraints.
+
+// CHECK: pdl.pattern @VarWithRangeConstraints
+// CHECK: %[[OPERAND_TYPES:.*]] = types
+// CHECK: %[[OPERANDS:.*]] = operands : %[[OPERAND_TYPES]]
+// CHECK: %[[RESULT_TYPES:.*]] = types
+// CHECK: operation(%[[OPERANDS]] : !pdl.range<value>)  -> (%[[RESULT_TYPES]] : !pdl.range<type>)
+Pattern VarWithRangeConstraints {
+  erase op<>(operands: ValueRange<operandTypes: TypeRange>) -> (results: TypeRange);
+}
+
+// -----
+
+// Test single entity constraints.
+
+// CHECK: pdl.pattern @VarWithConstraints
+// CHECK: %[[OPERAND_TYPE:.*]] = type
+// CHECK: %[[OPERAND:.*]] = operand : %[[OPERAND_TYPES]]
+// CHECK: %[[ATTR_TYPE:.*]] = type
+// CHECK: %[[ATTR:.*]] = attribute : %[[ATTR_TYPE]]
+// CHECK: %[[RESULT_TYPE:.*]] = type
+// CHECK: operation(%[[OPERAND]] : !pdl.value)  {"attr" = %[[ATTR]]} -> (%[[RESULT_TYPE]] : !pdl.type)
+Pattern VarWithConstraints {
+  erase op<>(operand: Value<operandType: Type>) { attr = _: Attr<attrType: Type>} -> (result: Type);
+}
+
+// -----
+
+// Test op constraint.
+
+// CHECK: pdl.pattern @VarWithNoNameOpConstraint
+// CHECK: %[[OPERANDS:.*]] = operands
+// CHECK: %[[RESULT_TYPES:.*]] = types
+// CHECK: operation(%[[OPERANDS]] : !pdl.range<value>)  -> (%[[RESULT_TYPES]] : !pdl.range<type>)
+Pattern VarWithNoNameOpConstraint => erase _: Op;
+
+// CHECK: pdl.pattern @VarWithNamedOpConstraint
+// CHECK: %[[OPERANDS:.*]] = operands
+// CHECK: %[[RESULT_TYPES:.*]] = types
+// CHECK: operation "test.op"(%[[OPERANDS]] : !pdl.range<value>)  -> (%[[RESULT_TYPES]] : !pdl.range<type>)
+Pattern VarWithNamedOpConstraint => erase _: Op<test.op>;
+
+// -----
+
+// Test user defined constraints.
+
+// CHECK: pdl.pattern @VarWithUserConstraint
+// CHECK: %[[OPERANDS:.*]] = operands
+// CHECK: %[[RESULT_TYPES:.*]] = types
+// CHECK: %[[OP:.*]] = operation(%[[OPERANDS]] : !pdl.range<value>)  -> (%[[RESULT_TYPES]] : !pdl.range<type>)
+// CHECK: apply_native_constraint "NestedArgCst"(%[[OP]] : !pdl.operation)
+// CHECK: apply_native_constraint "NestedResCst"(%[[OP]] : !pdl.operation)
+// CHECK: apply_native_constraint "OpCst"(%[[OP]] : !pdl.operation)
+// CHECK: rewrite %[[OP]]
+Constraint NestedArgCst(op: Op);
+Constraint NestedResCst(op: Op);
+Constraint TestArgResCsts(op: NestedArgCst) -> NestedResCst => op;
+Constraint OpCst(op: Op);
+Pattern VarWithUserConstraint => erase _: [TestArgResCsts, OpCst];
diff --git a/mlir/test/mlir-pdll/CodeGen/MLIR/expr.pdll b/mlir/test/mlir-pdll/CodeGen/MLIR/expr.pdll
new file mode 100644
--- /dev/null
+++ b/mlir/test/mlir-pdll/CodeGen/MLIR/expr.pdll
@@ -0,0 +1,93 @@
+// RUN: mlir-pdll %s -I %S -split-input-file -x mlir | FileCheck %s
+
+//===----------------------------------------------------------------------===//
+// AttributeExpr
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern @AttrExpr
+// CHECK: %[[ATTR:.*]] = attribute 10
+// CHECK: operation({{.*}}) {"attr" = %[[ATTR]]}
+Pattern AttrExpr => erase op<> { attr = attr<"10"> };
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// CallExpr
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern @TestCallWithArgsAndReturn
+// CHECK: %[[ROOT:.*]] = operation
+// CHECK: rewrite %[[ROOT]]
+// CHECK: %[[REPL_OP:.*]] = operation "test.op"
+// CHECK: %[[RESULTS:.*]] = results of %[[REPL_OP]]
+// CHECK: replace %[[ROOT]] with(%[[RESULTS]] : !pdl.range<value>)
+Rewrite TestRewrite(root: Op) -> ValueRange => root;
+Pattern TestCallWithArgsAndReturn => replace root: Op with TestRewrite(op<test.op>);
+
+// -----
+
+// CHECK: pdl.pattern @TestExternalCall
+// CHECK: %[[ROOT:.*]] = operation
+// CHECK: rewrite %[[ROOT]]
+// CHECK: %[[RESULTS:.*]] = apply_native_rewrite "TestRewrite"(%[[ROOT]] : !pdl.operation) : !pdl.range<value>
+// CHECK: replace %[[ROOT]] with(%[[RESULTS]] : !pdl.range<value>)
+Rewrite TestRewrite(op: Op) -> ValueRange;
+Pattern TestExternalCall => replace root: Op with TestRewrite(root);
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// MemberAccessExpr
+//===----------------------------------------------------------------------===//
+
+// Handle implicit "all" operation results access.
+// CHECK: pdl.pattern @OpAllResultMemberAccess
+// CHECK: %[[OP0:.*]] = operation
+// CHECK: %[[OP0_RES:.*]] = result 0 of %[[OP0]]
+// CHECK: %[[OP1:.*]] = operation
+// CHECK: %[[OP1_RES:.*]] = results of %[[OP1]]
+// CHECK: operation(%[[OP0_RES]], %[[OP1_RES]] : !pdl.value, !pdl.range<value>)
+Pattern OpAllResultMemberAccess {
+  let singleVar: Value = op<>;
+  let rangeVar: ValueRange = op<>;
+  erase op<>(singleVar, rangeVar);
+}
+
+// -----
+
+// CHECK: pdl.pattern @TupleMemberAccessNumber
+// CHECK: %[[FIRST:.*]] = operation "test.first"
+// CHECK: %[[SECOND:.*]] = operation "test.second"
+// CHECK: rewrite %[[FIRST]] {
+// CHECK:   replace %[[FIRST]] with %[[SECOND]]
+Pattern TupleMemberAccessNumber {
+  let firstOp = op<test.first>;
+  let secondOp = op<test.second>(firstOp);
+  let tuple = (firstOp, secondOp);
+  replace tuple.0 with tuple.1;
+}
+
+// -----
+
+// CHECK: pdl.pattern @TupleMemberAccessName
+// CHECK: %[[FIRST:.*]] = operation "test.first"
+// CHECK: %[[SECOND:.*]] = operation "test.second"
+// CHECK: rewrite %[[FIRST]] {
+// CHECK:   replace %[[FIRST]] with %[[SECOND]]
+Pattern TupleMemberAccessName {
+  let firstOp = op<test.first>;
+  let secondOp = op<test.second>(firstOp);
+  let tuple = (first = firstOp, second = secondOp);
+  replace tuple.first with tuple.second;
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// TypeExpr
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern @TypeExpr
+// CHECK: %[[TYPE:.*]] = type : i32
+// CHECK: operation({{.*}}) -> (%[[TYPE]] : !pdl.type)
+Pattern TypeExpr => erase op<> -> (type<"i32">);
diff --git a/mlir/test/mlir-pdll/CodeGen/MLIR/stmt.pdll b/mlir/test/mlir-pdll/CodeGen/MLIR/stmt.pdll
new file mode 100644
--- /dev/null
+++ b/mlir/test/mlir-pdll/CodeGen/MLIR/stmt.pdll
@@ -0,0 +1,61 @@
+// RUN: mlir-pdll %s -I %S -split-input-file -x mlir | FileCheck %s
+
+//===----------------------------------------------------------------------===//
+// EraseStmt
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern @EraseStmt
+// CHECK: %[[OP:.*]] = operation
+// CHECK: rewrite %[[OP]]
+// CHECK:   erase %[[OP]]
+Pattern EraseStmt => erase op<>;
+
+// -----
+
+// CHECK: pdl.pattern @EraseStmtNested
+// CHECK: %[[OP:.*]] = operation
+// CHECK: rewrite %[[OP]]
+// CHECK:   erase %[[OP]]
+Pattern EraseStmtNested => rewrite root: Op with { erase root; };
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// ReplaceStmt
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern @ReplaceStmt
+// CHECK: %[[OPERANDS:.*]] = operands
+// CHECK: %[[OP:.*]] = operation(%[[OPERANDS]]
+// CHECK: rewrite %[[OP]]
+// CHECK:   replace %[[OP]] with(%[[OPERANDS]] : !pdl.range<value>)
+Pattern ReplaceStmt => replace op<>(operands: ValueRange) with operands;
+
+// -----
+
+// CHECK: pdl.pattern @ReplaceStmtNested
+// CHECK: %[[OPERANDS:.*]] = operands
+// CHECK: %[[OP:.*]] = operation(%[[OPERANDS]]
+// CHECK: rewrite %[[OP]]
+// CHECK:   replace %[[OP]] with(%[[OPERANDS]] : !pdl.range<value>)
+Pattern ReplaceStmtNested {
+  let root = op<>(operands: ValueRange);
+  rewrite root with { replace root with operands; };
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// RewriteStmt
+//===----------------------------------------------------------------------===//
+
+// CHECK: pdl.pattern @RewriteStmtNested
+// CHECK: %[[OP:.*]] = operation
+// CHECK: rewrite %[[OP]]
+// CHECK:   erase %[[OP]]
+Pattern RewriteStmtNested {
+  rewrite root: Op with {
+    rewrite root with { erase root; };
+  };
+}
+
diff --git a/mlir/test/mlir-pdll/Parser/lit.local.cfg b/mlir/test/mlir-pdll/lit.local.cfg
rename from mlir/test/mlir-pdll/Parser/lit.local.cfg
rename to mlir/test/mlir-pdll/lit.local.cfg
diff --git a/mlir/tools/mlir-pdll/CMakeLists.txt b/mlir/tools/mlir-pdll/CMakeLists.txt
--- a/mlir/tools/mlir-pdll/CMakeLists.txt
+++ b/mlir/tools/mlir-pdll/CMakeLists.txt
@@ -1,5 +1,6 @@
 set(LIBS
   MLIRPDLLAST
+  MLIRPDLLCodeGen
   MLIRPDLLParser
   )
 
diff --git a/mlir/tools/mlir-pdll/mlir-pdll.cpp b/mlir/tools/mlir-pdll/mlir-pdll.cpp
--- a/mlir/tools/mlir-pdll/mlir-pdll.cpp
+++ b/mlir/tools/mlir-pdll/mlir-pdll.cpp
@@ -6,10 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "mlir/IR/BuiltinOps.h"
 #include "mlir/Support/FileUtilities.h"
 #include "mlir/Support/ToolUtilities.h"
 #include "mlir/Tools/PDLL/AST/Context.h"
 #include "mlir/Tools/PDLL/AST/Nodes.h"
+#include "mlir/Tools/PDLL/CodeGen/MLIRGen.h"
 #include "mlir/Tools/PDLL/Parser/Parser.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/InitLLVM.h"
@@ -26,6 +28,7 @@
 /// The desired output type.
 enum class OutputType {
   AST,
+  MLIR,
 };
 
 static LogicalResult
@@ -40,12 +43,18 @@
   if (failed(module))
     return failure();
 
-  switch (outputType) {
-  case OutputType::AST:
+  if (outputType == OutputType::AST) {
     (*module)->print(os);
-    break;
+    return success();
   }
 
+  MLIRContext mlirContext;
+  OwningOpRef<ModuleOp> pdlModule =
+      codegenPDLLToMLIR(&mlirContext, astContext, sourceMgr, **module);
+  if (!pdlModule)
+    return failure();
+
+  pdlModule->print(os, OpPrintingFlags().enableDebugInfo());
   return success();
 }
 
@@ -71,7 +80,9 @@
       "x", llvm::cl::init(OutputType::AST),
       llvm::cl::desc("The type of output desired"),
       llvm::cl::values(clEnumValN(OutputType::AST, "ast",
-                                  "generate the AST for the input file")));
+                                  "generate the AST for the input file"),
+                       clEnumValN(OutputType::MLIR, "mlir",
+                                  "generate the PDL MLIR for the input file")));
 
   llvm::InitLLVM y(argc, argv);
   llvm::cl::ParseCommandLineOptions(argc, argv, "PDLL Frontend");