[mlir][PDLL] Add an initial frontend for PDLL

[rriddle]

Summary

This is a new pattern rewrite frontend designed from the ground
up to support MLIR constructs, and to target PDL. This frontend
language was proposed in https://llvm.discourse.group/t/rfc-pdll-a-new-declarative-rewrite-frontend-for-mlir/4798

This commit starts sketching out the base structure of the
frontend, and is intended to be a minimal starting point for
building up the language. It essentially contains support for
defining a pattern, variables, and erasing an operation. The
features mentioned in the proposal RFC (including IDE support)
will be added incrementally in followup commits.

I intend to upstream the documentation for the language in a
followup when a bit more of the pieces have been landed.

[bondhugula]

Bikeshed: Is PDLL itself also the name of the frontend? As an analogy, is PDLL the clang or C++ or both?

[nicolasvasilache]

mlir/include/mlir/Tools/PDLL/AST/Diagnostic.h

2

Since this looks similar to other diagnostics, is there a common impl that this should just reuse?
I assume not, so I'd be interested in the features that are PDLL specific.

mlir/include/mlir/Tools/PDLL/AST/Nodes.h

691

nit: nl

mlir/include/mlir/Tools/PDLL/Parser/Parser.h

35

nit: nl

mlir/lib/Tools/PDLL/AST/Nodes.cpp

21

I have a hard deciding what happens here, I see this ctor calling into strLen that looks for \0:

class StringRef {
    /// Construct a string ref from a cstring.
    /*implicit*/ constexpr StringRef(const char *Str)
        : Data(Str), Length(Str ? strLen(Str) : 0) {}
}

Consider return StringRef("", 0); ?

75

I assume this is the stuff you'd want to fill once you also have a grammar, but for now this CL is the minimal basic shell and plumbing.

mlir/lib/Tools/PDLL/AST/Types.cpp

125

nit: nl

mlir/lib/Tools/PDLL/Parser/Lexer.h

222

nit: nl

222

nit: nl

mlir/lib/Tools/PDLL/Parser/Parser.cpp

267

Should there be some minimal grammar doc here and below, or is it part of the followup doc commit?

706

Seems to not be covered by tests?

[Mogball]

mlir/lib/Tools/PDLL/AST/Nodes.cpp

225

Why not a unique_ptr?

mlir/lib/Tools/PDLL/Parser/Lexer.cpp

133

*curBuffer.end() is fine because the string is null-terminated right?

mlir/lib/Tools/PDLL/Parser/Parser.cpp

150

I think this function, at least, could use some documentation.

267

+1

[rriddle]

rebase

[rriddle]

In D115093#3171409, @bondhugula wrote:

Bikeshed: Is PDLL itself also the name of the frontend? As an analogy, is PDLL the clang or C++ or both?

It's both. Kind of like how Tablegen is both the language and frontend. For small/specialized languages I (personally) don't see a reason to make a distinction.

[jpienaar]

mlir/include/mlir/Tools/PDLL/AST/Context.h

44

Micro nit: newline

mlir/include/mlir/Tools/PDLL/AST/Diagnostic.h

2

Good question, would be good to capture why we couldn't use those - currently I'm not sure why we have this in mlir/include/mlir vs in mlir/tools/pdll (or similar) , do we actually expect these headers to be used by any other parts of MLIR infra or is this a standalone tool?

mlir/lib/Tools/PDLL/Parser/Lexer.cpp

378

Newline?

[rriddle]

mlir/include/mlir/Tools/PDLL/AST/Diagnostic.h

2

This is actually in mlir/Tools which was created specifically for code that is used by multiple tools (i.e. not used by the infra itself), which is useful because it allows for proper library layering (w.r.t internal/external includes), among other reasons. There are at least 2 individual tools that will use the code exposed here (mlir-pdll, and the language server).

Will add a comment as to why we can't share with the Diagnostics in mlir/IR (mainly because we don't want to use MLIR infra here, which is slower (e.g. uniquing things that we don't need to, we use the direct SMLoc/SMRange), and brings an otherwise unnecessary dependency. Essentially this is just a stripped down version, which is different enough that sharing would be more work than it's worth (with templates and things).

[jpienaar]

Nice, thanks

mlir/include/mlir/Tools/PDLL/AST/Types.h

97

So this is the meet ? Also any errors possible here?

mlir/lib/Tools/PDLL/AST/Nodes.cpp

167

Context is a little bit generic for me, if kept within the tool fine. If this will be used LSP side (where we already have MLIRContext) then I'd rather be explicit PDLLContext

mlir/lib/Tools/PDLL/Parser/Lexer.h

48

Section heading?

mlir/lib/Tools/PDLL/Parser/Parser.cpp

49

Would it be pissible to add here what the difference is? (e.g., why do we care about these 2 and only these two, why not have it have be a nesting of parser context etc)

164

Is this newline indicative of something?

240

(I sort of would have expected that this would just be a ScopedHashTable)

944

I'm not sure if TypeSwitch here brings as much value (feels like it is using a lot of horizontal whitespace and makes it less readable than plain variant, but OK)

1066

Why is this needed?

mlir/tools/mlir-pdll/mlir-pdll.cpp

26

Could we move these inside main (as we did with MlirOptMain)?

78

Do you need an InitLLVM?

[rriddle]

resolve comments

mlir/include/mlir/Tools/PDLL/AST/Types.h

97

Essentially, added a note on failure returning null.

mlir/lib/Tools/PDLL/AST/Nodes.cpp

75

Yeah, this all is generally just filler for separating things.

167

I think it is fine given that the Context is nested within mlir::pdll::ast. When used with the LSP, it would either be ast::Context (if we add using namespace mlir::pdll, which could be fine given the context.. hehe) or pdll::ast::Context. If you feel strongly I can change it, but I plan to another context in a followup; i.e. mlir::pdll::ods::Context. Having ast::Context and ods::Context felt cleaner than ast::PDLLASTContext, ods::PDLLODSContext (given that I don't plan to add usings for either ast or ods namespaces in generic code).

225

For Module in particular? or all AST nodes? For AST nodes, using trailing storage and BumpPtrAllocator is much more efficient than std::unique_ptr given the memory locality and greatly reduced malloc traffic. For Module in particular, given that it is an AST node there is not much benefit in treating it differently than the others IMO (AST nodes don't really need to be de-allocated).

mlir/lib/Tools/PDLL/Parser/Lexer.cpp

133

Yep, indexing the end of the buffer is safe because it's null-terminated.

mlir/lib/Tools/PDLL/Parser/Parser.cpp

49

There will be a few more added in followups, this is essentially used just for verification purposes so we don't need to nest the parser or anything like that. For example, this makes it easier to verify that we don't use a rewrite statement inside of a constraint, call user defined rewrites from inside of a "match" section, etc.

240

It isn't a scoped hash table because the scope may live beyond its use in the parser process. For example, we often give a scope to the LSP for things like code completion. For templates, we may temporarily switch the scope back to the parent of the template when doing instantiations.

(Simplified scopes a bit by moving management to the parser, I originally had them in the AST in case we need to manage scopes from an AST node directly, but I don't have a direct need for that yet)

267

It's part of a followup that adds proper frontend documentation (I want to make sure everything really important is captured in user facing docs). Will add a few comments here for now though.

[rriddle]

update

[rriddle]

rebase

mlir/include/mlir/Tools/PDLL/AST/Context.h

+//===- Context.h - PDLL AST Context -----------------------------*- 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_AST_CONTEXT_H_
+#define MLIR_TOOLS_PDLL_AST_CONTEXT_H_
+
+#include "mlir/Support/StorageUniquer.h"
+#include "mlir/Tools/PDLL/AST/Diagnostic.h"
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+/// This class represents the main context of the PDLL AST. It handles
+/// allocating all of the AST constructs, and manages all state necessary for
+/// the AST.
+class Context {
+public:
+  Context();
+  Context(const Context &) = delete;
+  Context &operator=(const Context &) = delete;
+
+  /// Return the allocator owned by this context.
+  llvm::BumpPtrAllocator &getAllocator() { return allocator; }
+
+  /// Return the storage uniquer used for AST types.
+  StorageUniquer &getTypeUniquer() { return typeUniquer; }
+
+  /// Return the diagnostic engine of this context.
+  DiagnosticEngine &getDiagEngine() { return diagEngine; }
+
+private:
+  /// The diagnostic engine of this AST context.
+  DiagnosticEngine diagEngine;
+
+  /// The allocator used for AST nodes, and other entities allocated within the
+  /// context.
+  llvm::BumpPtrAllocator allocator;
+
+  /// The uniquer used for creating AST types.
+  StorageUniquer typeUniquer;
+};
+
+} // namespace ast
+} // namespace pdll
+} // namespace mlir
+
+#endif // MLIR_TOOLS_PDLL_AST_CONTEXT_H_

mlir/include/mlir/Tools/PDLL/AST/Diagnostic.h

+//===- Diagnostic.h - PDLL AST Diagnostics ----------------------*- 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_AST_DIAGNOSTICS_H_
+#define MLIR_TOOLS_PDLL_AST_DIAGNOSTICS_H_
+
+#include <string>
+
+#include "mlir/Support/LLVM.h"
+#include "mlir/Support/LogicalResult.h"
+#include "llvm/ADT/FunctionExtras.h"
+#include "llvm/Support/SourceMgr.h"
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+class DiagnosticEngine;
+
+//===----------------------------------------------------------------------===//
+// Diagnostic
+//===----------------------------------------------------------------------===//
+
+/// This class provides a simple implementation of a PDLL diagnostic.
+class Diagnostic {
+public:
+  using Severity = llvm::SourceMgr::DiagKind;
+
+  /// Return the severity of this diagnostic.
+  Severity getSeverity() const { return severity; }
+
+  /// Return the message of this diagnostic.
+  StringRef getMessage() const { return message; }
+
+  /// Return the location of this diagnostic.
+  llvm::SMRange getLocation() const { return location; }
+
+  /// Return the notes of this diagnostic.
+  auto getNotes() const { return llvm::make_pointee_range(notes); }
+
+  /// Attach a note to this diagnostic.
+  Diagnostic &attachNote(const Twine &msg,
+                         Optional<llvm::SMRange> noteLoc = llvm::None) {
+    assert(getSeverity() != Severity::DK_Note &&
+           "cannot attach a Note to a Note");
+    notes.emplace_back(
+        new Diagnostic(Severity::DK_Note, noteLoc.getValueOr(location), msg));
+    return *notes.back();
+  }
+
+  /// Allow an inflight diagnostic to be converted to 'failure', otherwise
+  /// 'success' if this is an empty diagnostic.
+  operator LogicalResult() const { return failure(); }
+
+private:
+  Diagnostic(Severity severity, llvm::SMRange loc, const Twine &msg)
+      : severity(severity), message(msg.str()), location(loc) {}
+
+  // Allow access to the constructor.
+  friend DiagnosticEngine;
+
+  /// The severity of this diagnostic.
+  Severity severity;
+  /// The message held by this diagnostic.
+  std::string message;
+  /// The raw location of this diagnostic.
+  llvm::SMRange location;
+  /// Any additional note diagnostics attached to this diagnostic.
+  std::vector<std::unique_ptr<Diagnostic>> notes;
+};
+
+//===----------------------------------------------------------------------===//
+// InFlightDiagnostic
+//===----------------------------------------------------------------------===//
+
+/// This class represents a diagnostic that is inflight and set to be reported.
+/// This allows for last minute modifications of the diagnostic before it is
+/// emitted by a DiagnosticEngine.
+class InFlightDiagnostic {
+public:
+  InFlightDiagnostic() = default;
+  InFlightDiagnostic(InFlightDiagnostic &&rhs)
+      : owner(rhs.owner), impl(std::move(rhs.impl)) {
+    // Reset the rhs diagnostic.
+    rhs.impl.reset();
+    rhs.abandon();
+  }
+  ~InFlightDiagnostic() {
+    if (isInFlight())
+      report();
+  }
+
+  /// Access the internal diagnostic.
+  Diagnostic &operator*() { return *impl; }
+  Diagnostic *operator->() { return &*impl; }
+
+  /// Reports the diagnostic to the engine.
+  void report();
+
+  /// Abandons this diagnostic so that it will no longer be reported.
+  void abandon() { owner = nullptr; }
+
+  /// Allow an inflight diagnostic to be converted to 'failure', otherwise
+  /// 'success' if this is an empty diagnostic.
+  operator LogicalResult() const { return failure(isActive()); }
+
+private:
+  InFlightDiagnostic &operator=(const InFlightDiagnostic &) = delete;
+  InFlightDiagnostic &operator=(InFlightDiagnostic &&) = delete;
+  InFlightDiagnostic(DiagnosticEngine *owner, Diagnostic &&rhs)
+      : owner(owner), impl(std::move(rhs)) {}
+
+  /// Returns true if the diagnostic is still active, i.e. it has a live
+  /// diagnostic.
+  bool isActive() const { return impl.hasValue(); }
+
+  /// Returns true if the diagnostic is still in flight to be reported.
+  bool isInFlight() const { return owner; }
+
+  // Allow access to the constructor.
+  friend DiagnosticEngine;
+
+  /// The engine that this diagnostic is to report to.
+  DiagnosticEngine *owner = nullptr;
+
+  /// The raw diagnostic that is inflight to be reported.
+  Optional<Diagnostic> impl;
+};
+
+//===----------------------------------------------------------------------===//
+// DiagnosticEngine
+//===----------------------------------------------------------------------===//
+
+/// This class manages the construction and emission of PDLL diagnostics.
+class DiagnosticEngine {
+public:
+  /// A function used to handle diagnostics emitted by the engine.
+  using HandlerFn = llvm::unique_function<void(Diagnostic &)>;
+
+  /// Emit an error to the diagnostic engine.
+  InFlightDiagnostic emitError(llvm::SMRange loc, const Twine &msg) {
+    return InFlightDiagnostic(
+        this, Diagnostic(Diagnostic::Severity::DK_Error, loc, msg));
+  }
+  InFlightDiagnostic emitWarning(llvm::SMRange loc, const Twine &msg) {
+    return InFlightDiagnostic(
+        this, Diagnostic(Diagnostic::Severity::DK_Warning, loc, msg));
+  }
+
+  /// Report the given diagnostic.
+  void report(Diagnostic &&diagnostic) {
+    if (handler)
+      handler(diagnostic);
+  }
+
+  /// Get the current handler function of this diagnostic engine.
+  const HandlerFn &getHandlerFn() const { return handler; }
+
+  /// Take the current handler function, resetting the current handler to null.
+  HandlerFn takeHandlerFn() {
+    HandlerFn oldHandler = std::move(handler);
+    handler = {};
+    return oldHandler;
+  }
+
+  /// Set the handler function for this diagnostic engine.
+  void setHandlerFn(HandlerFn &&newHandler) { handler = std::move(newHandler); }
+
+private:
+  /// The registered diagnostic handler function.
+  HandlerFn handler;
+};
+
+} // namespace ast
+} // namespace pdll
+} // namespace mlir
+
+#endif // MLIR_TOOLS_PDLL_AST_DIAGNOSTICS_H_

mlir/include/mlir/Tools/PDLL/AST/Nodes.h

+//===- Nodes.h --------------------------------------------------*- 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_AST_NODES_H_
+#define MLIR_TOOLS_PDLL_AST_NODES_H_
+
+#include "mlir/Support/LLVM.h"
+#include "mlir/Tools/PDLL/AST/Types.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/SMLoc.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/TrailingObjects.h"
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+class Context;
+class Decl;
+class Expr;
+class OpNameDecl;
+class VariableDecl;
+
+//===----------------------------------------------------------------------===//
+// Name
+//===----------------------------------------------------------------------===//
+
+/// This class provides a convenient API for interacting with source names. It
+/// contains a string name as well as the source location for that name.
+struct Name {
+  static const Name &create(Context &ctx, StringRef name,
+                            llvm::SMRange location);
+
+  /// Return the raw string name.
+  StringRef getName() const { return name; }
+
+  /// Get the location of this name.
+  llvm::SMRange getLoc() const { return location; }
+
+private:
+  Name() = delete;
+  Name(const Name &) = delete;
+  Name &operator=(const Name &) = delete;
+  Name(StringRef name, llvm::SMRange location)
+      : name(name), location(location) {}
+
+  /// The string name of the decl.
+  StringRef name;
+  /// The location of the decl name.
+  llvm::SMRange location;
+};
+
+//===----------------------------------------------------------------------===//
+// DeclScope
+//===----------------------------------------------------------------------===//
+
+/// This class represents a scope for named AST decls. A scope determines the
+/// visibility and lifetime of a named declaration.
+class DeclScope {
+public:
+  /// Create a new scope with an optional parent scope.
+  DeclScope(DeclScope *parent = nullptr) : parent(parent) {}
+
+  /// Return the parent scope of this scope, or nullptr if there is no parent.
+  DeclScope *getParentScope() { return parent; }
+  const DeclScope *getParentScope() const { return parent; }
+
+  /// Return all of the decls within this scope.
+  auto getDecls() const { return llvm::make_second_range(decls); }
+
+  /// Add a new decl to the scope.
+  void add(Decl *decl);
+
+  /// Lookup a decl with the given name starting from this scope. Returns
+  /// nullptr if no decl could be found.
+  Decl *lookup(StringRef name);
+  template <typename T>
+  T *lookup(StringRef name) {
+    return dyn_cast_or_null<T>(lookup(name));
+  }
+  const Decl *lookup(StringRef name) const {
+    return const_cast<DeclScope *>(this)->lookup(name);
+  }
+  template <typename T>
+  const T *lookup(StringRef name) const {
+    return dyn_cast_or_null<T>(lookup(name));
+  }
+
+private:
+  /// The parent scope, or null if this is a top-level scope.
+  DeclScope *parent;
+  /// The decls defined within this scope.
+  llvm::StringMap<Decl *> decls;
+};
+
+//===----------------------------------------------------------------------===//
+// Node
+//===----------------------------------------------------------------------===//
+
+/// This class represents a base AST node. All AST nodes are derived from this
+/// class, and it contains many of the base functionality for interacting with
+/// nodes.
+class Node {
+public:
+  /// This CRTP class provides several utilies when defining new AST nodes.
+  template <typename T, typename BaseT>
+  class NodeBase : public BaseT {
+  public:
+    using Base = NodeBase<T, BaseT>;
+
+    /// Provide type casting support.
+    static bool classof(const Node *node) {
+      return node->getTypeID() == TypeID::get<T>();
+    }
+
+  protected:
+    template <typename... Args>
+    explicit NodeBase(llvm::SMRange loc, Args &&...args)
+        : BaseT(TypeID::get<T>(), loc, std::forward<Args>(args)...) {}
+  };
+
+  /// Return the type identifier of this node.
+  TypeID getTypeID() const { return typeID; }
+
+  /// Return the location of this node.
+  llvm::SMRange getLoc() const { return loc; }
+
+  /// Print this node to the given stream.
+  void print(raw_ostream &os) const;
+
+protected:
+  Node(TypeID typeID, llvm::SMRange loc) : typeID(typeID), loc(loc) {}
+
+private:
+  /// A unique type identifier for this node.
+  TypeID typeID;
+
+  /// The location of this node.
+  llvm::SMRange loc;
+};
+
+//===----------------------------------------------------------------------===//
+// Stmt
+//===----------------------------------------------------------------------===//
+
+/// This class represents a base AST Statement node.
+class Stmt : public Node {
+public:
+  using Node::Node;
+
+  /// Provide type casting support.
+  static bool classof(const Node *node);
+};
+
+//===----------------------------------------------------------------------===//
+// CompoundStmt
+//===----------------------------------------------------------------------===//
+
+/// This statement represents a compound statement, which contains a collection
+/// of other statements.
+class CompoundStmt final : public Node::NodeBase<CompoundStmt, Stmt>,
+                           private llvm::TrailingObjects<CompoundStmt, Stmt *> {
+public:
+  static CompoundStmt *create(Context &ctx, llvm::SMRange location,
+                              ArrayRef<Stmt *> children);
+
+  /// Return the children of this compound statement.
+  MutableArrayRef<Stmt *> getChildren() {
+    return {getTrailingObjects<Stmt *>(), numChildren};
+  }
+  ArrayRef<Stmt *> getChildren() const {
+    return const_cast<CompoundStmt *>(this)->getChildren();
+  }
+  ArrayRef<Stmt *>::iterator begin() const { return getChildren().begin(); }
+  ArrayRef<Stmt *>::iterator end() const { return getChildren().end(); }
+
+private:
+  CompoundStmt(llvm::SMRange location, unsigned numChildren)
+      : Base(location), numChildren(numChildren) {}
+
+  /// The number of held children statements.
+  unsigned numChildren;
+
+  // Allow access to various privates.
+  friend class llvm::TrailingObjects<CompoundStmt, Stmt *>;
+};
+
+//===----------------------------------------------------------------------===//
+// LetStmt
+//===----------------------------------------------------------------------===//
+
+/// This statement represents a `let` statement in PDLL. This statement is used
+/// to define variables.
+class LetStmt final : public Node::NodeBase<LetStmt, Stmt> {
+public:
+  static LetStmt *create(Context &ctx, llvm::SMRange loc,
+                         VariableDecl *varDecl);
+
+  /// Return the variable defined by this statement.
+  VariableDecl *getVarDecl() const { return varDecl; }
+
+private:
+  LetStmt(llvm::SMRange loc, VariableDecl *varDecl)
+      : Base(loc), varDecl(varDecl) {}
+
+  /// The variable defined by this statement.
+  VariableDecl *varDecl;
+};
+
+//===----------------------------------------------------------------------===//
+// OpRewriteStmt
+//===----------------------------------------------------------------------===//
+
+/// This class represents a base operation rewrite statement. Operation rewrite
+/// statements perform a set of transformations on a given root operation.
+class OpRewriteStmt : public Stmt {
+public:
+  /// Provide type casting support.
+  static bool classof(const Node *node);
+
+  /// Return the root operation of this rewrite.
+  Expr *getRootOpExpr() const { return rootOp; }
+
+protected:
+  OpRewriteStmt(TypeID typeID, llvm::SMRange loc, Expr *rootOp)
+      : Stmt(typeID, loc), rootOp(rootOp) {}
+
+protected:
+  /// The root operation being rewritten.
+  Expr *rootOp;
+};
+
+//===----------------------------------------------------------------------===//
+// EraseStmt
+
+/// This statement represents the `erase` statement in PDLL. This statement
+/// erases the given root operation, corresponding roughly to the
+/// PatternRewriter::eraseOp API.
+class EraseStmt final : public Node::NodeBase<EraseStmt, OpRewriteStmt> {
+public:
+  static EraseStmt *create(Context &ctx, llvm::SMRange loc, Expr *rootOp);
+
+private:
+  EraseStmt(llvm::SMRange loc, Expr *rootOp) : Base(loc, rootOp) {}
+};
+
+//===----------------------------------------------------------------------===//
+// Expr
+//===----------------------------------------------------------------------===//
+
+/// This class represents a base AST Expression node.
+class Expr : public Stmt {
+public:
+  /// Return the type of this expression.
+  Type getType() const { return type; }
+
+  /// Provide type casting support.
+  static bool classof(const Node *node);
+
+protected:
+  Expr(TypeID typeID, llvm::SMRange loc, Type type)
+      : Stmt(typeID, loc), type(type) {}
+
+private:
+  /// The type of this expression.
+  Type type;
+};
+
+//===----------------------------------------------------------------------===//
+// DeclRefExpr
+//===----------------------------------------------------------------------===//
+
+/// This expression represents a reference to a Decl node.
+class DeclRefExpr : public Node::NodeBase<DeclRefExpr, Expr> {
+public:
+  static DeclRefExpr *create(Context &ctx, llvm::SMRange loc, Decl *decl,
+                             Type type);
+
+  /// Get the decl referenced by this expression.
+  Decl *getDecl() const { return decl; }
+
+private:
+  DeclRefExpr(llvm::SMRange loc, Decl *decl, Type type)
+      : Base(loc, type), decl(decl) {}
+
+  /// The decl referenced by this expression.
+  Decl *decl;
+};
+
+//===----------------------------------------------------------------------===//
+// MemberAccessExpr
+//===----------------------------------------------------------------------===//
+
+/// This expression represents a named member or field access of a given parent
+/// expression.
+class MemberAccessExpr : public Node::NodeBase<MemberAccessExpr, Expr> {
+public:
+  static MemberAccessExpr *create(Context &ctx, llvm::SMRange loc,
+                                  const Expr *parentExpr, StringRef memberName,
+                                  Type type);
+
+  /// Get the parent expression of this access.
+  const Expr *getParentExpr() const { return parentExpr; }
+
+  /// Return the name of the member being accessed.
+  StringRef getMemberName() const { return memberName; }
+
+private:
+  MemberAccessExpr(llvm::SMRange loc, const Expr *parentExpr,
+                   StringRef memberName, Type type)
+      : Base(loc, type), parentExpr(parentExpr), memberName(memberName) {}
+
+  /// The parent expression of this access.
+  const Expr *parentExpr;
+
+  /// The name of the member being accessed from the parent.
+  StringRef memberName;
+};
+
+//===----------------------------------------------------------------------===//
+// Decl
+//===----------------------------------------------------------------------===//
+
+/// This class represents the base Decl node.
+class Decl : public Node {
+public:
+  /// Return the name of the decl, or nullptr if it doesn't have one.
+  const Name *getName() const { return name; }
+
+  /// Provide type casting support.
+  static bool classof(const Node *node);
+
+protected:
+  Decl(TypeID typeID, llvm::SMRange loc, const Name *name = nullptr)
+      : Node(typeID, loc), name(name) {}
+
+private:
+  /// The name of the decl. This is optional for some decls, such as
+  /// PatternDecl.
+  const Name *name;
+};
+
+//===----------------------------------------------------------------------===//
+// ConstraintDecl
+//===----------------------------------------------------------------------===//
+
+/// This class represents the base of all AST Constraint decls. Constraints
+/// apply matcher conditions to, and define the type of PDLL variables.
+class ConstraintDecl : public Decl {
+public:
+  /// Provide type casting support.
+  static bool classof(const Node *node);
+
+protected:
+  ConstraintDecl(TypeID typeID, llvm::SMRange loc, const Name *name = nullptr)
+      : Decl(typeID, loc, name) {}
+};
+
+/// This class represents a reference to a constraint, and contains a constraint
+/// and the location of the reference.
+struct ConstraintRef {
+  ConstraintRef(const ConstraintDecl *constraint, llvm::SMRange refLoc)
+      : constraint(constraint), referenceLoc(refLoc) {}
+  explicit ConstraintRef(const ConstraintDecl *constraint)
+      : ConstraintRef(constraint, constraint->getLoc()) {}
+
+  const ConstraintDecl *constraint;
+  llvm::SMRange referenceLoc;
+};
+
+//===----------------------------------------------------------------------===//
+// CoreConstraintDecl
+//===----------------------------------------------------------------------===//
+
+/// This class represents the base of all "core" constraints. Core constraints
+/// are those that generally represent a concrete IR construct, such as
+/// `Type`s or `Value`s.
+class CoreConstraintDecl : public ConstraintDecl {
+public:
+  /// Provide type casting support.
+  static bool classof(const Node *node);
+
+protected:
+  CoreConstraintDecl(TypeID typeID, llvm::SMRange loc,
+                     const Name *name = nullptr)
+      : ConstraintDecl(typeID, loc, name) {}
+};
+
+//===----------------------------------------------------------------------===//
+// AttrConstraintDecl
+
+/// The class represents an Attribute constraint, and constrains a variable to
+/// be an Attribute.
+class AttrConstraintDecl
+    : public Node::NodeBase<AttrConstraintDecl, CoreConstraintDecl> {
+public:
+  static AttrConstraintDecl *create(Context &ctx, llvm::SMRange loc,
+                                    Expr *typeExpr = nullptr);
+
+  /// Return the optional type the attribute is constrained to.
+  Expr *getTypeExpr() { return typeExpr; }
+  const Expr *getTypeExpr() const { return typeExpr; }
+
+protected:
+  AttrConstraintDecl(llvm::SMRange loc, Expr *typeExpr)
+      : Base(loc), typeExpr(typeExpr) {}
+
+  /// An optional type that the attribute is constrained to.
+  Expr *typeExpr;
+};
+
+//===----------------------------------------------------------------------===//
+// OpConstraintDecl
+
+/// The class represents an Operation constraint, and constrains a variable to
+/// be an Operation.
+class OpConstraintDecl
+    : public Node::NodeBase<OpConstraintDecl, CoreConstraintDecl> {
+public:
+  static OpConstraintDecl *create(Context &ctx, llvm::SMRange loc,
+                                  const OpNameDecl *nameDecl = nullptr);
+
+  /// Return the name of the operation, or None if there isn't one.
+  Optional<StringRef> getName() const;
+
+  /// Return the declaration of the operation name.
+  const OpNameDecl *getNameDecl() const { return nameDecl; }
+
+protected:
+  explicit OpConstraintDecl(llvm::SMRange loc, const OpNameDecl *nameDecl)
+      : Base(loc), nameDecl(nameDecl) {}
+
+  /// The operation name of this constraint.
+  const OpNameDecl *nameDecl;
+};
+
+//===----------------------------------------------------------------------===//
+// TypeConstraintDecl
+
+/// The class represents a Type constraint, and constrains a variable to be a
+/// Type.
+class TypeConstraintDecl
+    : public Node::NodeBase<TypeConstraintDecl, CoreConstraintDecl> {
+public:
+  static TypeConstraintDecl *create(Context &ctx, llvm::SMRange loc);
+
+protected:
+  using Base::Base;
+};
+
+//===----------------------------------------------------------------------===//
+// TypeRangeConstraintDecl
+
+/// The class represents a TypeRange constraint, and constrains a variable to be
+/// a TypeRange.
+class TypeRangeConstraintDecl
+    : public Node::NodeBase<TypeRangeConstraintDecl, CoreConstraintDecl> {
+public:
+  static TypeRangeConstraintDecl *create(Context &ctx, llvm::SMRange loc);
+
+protected:
+  using Base::Base;
+};
+
+//===----------------------------------------------------------------------===//
+// ValueConstraintDecl
+
+/// The class represents a Value constraint, and constrains a variable to be a
+/// Value.
+class ValueConstraintDecl
+    : public Node::NodeBase<ValueConstraintDecl, CoreConstraintDecl> {
+public:
+  static ValueConstraintDecl *create(Context &ctx, llvm::SMRange loc,
+                                     Expr *typeExpr);
+
+  /// Return the optional type the value is constrained to.
+  Expr *getTypeExpr() { return typeExpr; }
+  const Expr *getTypeExpr() const { return typeExpr; }
+
+protected:
+  ValueConstraintDecl(llvm::SMRange loc, Expr *typeExpr)
+      : Base(loc), typeExpr(typeExpr) {}
+
+  /// An optional type that the value is constrained to.
+  Expr *typeExpr;
+};
+
+//===----------------------------------------------------------------------===//
+// ValueRangeConstraintDecl
+
+/// The class represents a ValueRange constraint, and constrains a variable to
+/// be a ValueRange.
+class ValueRangeConstraintDecl
+    : public Node::NodeBase<ValueRangeConstraintDecl, CoreConstraintDecl> {
+public:
+  static ValueRangeConstraintDecl *create(Context &ctx, llvm::SMRange loc,
+                                          Expr *typeExpr);
+
+  /// Return the optional type the value range is constrained to.
+  Expr *getTypeExpr() { return typeExpr; }
+  const Expr *getTypeExpr() const { return typeExpr; }
+
+protected:
+  ValueRangeConstraintDecl(llvm::SMRange loc, Expr *typeExpr)
+      : Base(loc), typeExpr(typeExpr) {}
+
+  /// An optional type that the value range is constrained to.
+  Expr *typeExpr;
+};
+
+//===----------------------------------------------------------------------===//
+// OpNameDecl
+//===----------------------------------------------------------------------===//
+
+/// This Decl represents an OperationName.
+class OpNameDecl : public Node::NodeBase<OpNameDecl, Decl> {
+public:
+  static OpNameDecl *create(Context &ctx, const Name &name);
+  static OpNameDecl *create(Context &ctx, llvm::SMRange loc);
+
+  /// Return the name of this operation, or none if the name is unknown.
+  Optional<StringRef> getName() const {
+    const Name *name = Decl::getName();
+    return name ? Optional<StringRef>(name->getName()) : llvm::None;
+  }
+
+private:
+  explicit OpNameDecl(const Name &name) : Base(name.getLoc(), &name) {}
+  explicit OpNameDecl(llvm::SMRange loc) : Base(loc) {}
+};
+
+//===----------------------------------------------------------------------===//
+// PatternDecl
+//===----------------------------------------------------------------------===//
+
+/// This Decl represents a single Pattern.
+class PatternDecl : public Node::NodeBase<PatternDecl, Decl> {
+public:
+  static PatternDecl *create(Context &ctx, llvm::SMRange location,
+                             const Name *name, Optional<uint16_t> benefit,
+                             bool hasBoundedRecursion,
+                             const CompoundStmt *body);
+
+  /// Return the benefit of this pattern if specified, or None.
+  Optional<uint16_t> getBenefit() const { return benefit; }
+
+  /// Return if this pattern has bounded rewrite recursion.
+  bool hasBoundedRewriteRecursion() const { return hasBoundedRecursion; }
+
+  /// Return the body of this pattern.
+  const CompoundStmt *getBody() const { return patternBody; }
+
+  /// Return the root rewrite statement of this pattern.
+  const OpRewriteStmt *getRootRewriteStmt() const {
+    return cast<OpRewriteStmt>(patternBody->getChildren().back());
+  }
+
+private:
+  PatternDecl(llvm::SMRange loc, const Name *name, Optional<uint16_t> benefit,
+              bool hasBoundedRecursion, const CompoundStmt *body)
+      : Base(loc, name), benefit(benefit),
+        hasBoundedRecursion(hasBoundedRecursion), patternBody(body) {}
+
+  /// The benefit of the pattern if it was explicitly specified, None otherwise.
+  Optional<uint16_t> benefit;
+
+  /// If the pattern has properly bounded rewrite recursion or not.
+  bool hasBoundedRecursion;
+
+  /// The compound statement representing the body of the pattern.
+  const CompoundStmt *patternBody;
+};
+
+//===----------------------------------------------------------------------===//
+// VariableDecl
+//===----------------------------------------------------------------------===//
+
+/// This Decl represents the definition of a PDLL variable.
+class VariableDecl final
+    : public Node::NodeBase<VariableDecl, Decl>,
+      private llvm::TrailingObjects<VariableDecl, ConstraintRef> {
+public:
+  static VariableDecl *create(Context &ctx, const Name &name, Type type,
+                              Expr *initExpr,
+                              ArrayRef<ConstraintRef> constraints);
+
+  /// Return the constraints of this variable.
+  ArrayRef<ConstraintRef> getConstraints() const {
+    return {getTrailingObjects<ConstraintRef>(), numConstraints};
+  }
+
+  /// Return the initializer expression of this statement, or nullptr if there
+  /// was no initializer.
+  Expr *getInitExpr() const { return initExpr; }
+
+  /// Return the name of the decl.
+  const Name &getName() const { return *Decl::getName(); }
+
+  /// Return the type of the decl.
+  Type getType() const { return type; }
+
+private:
+  VariableDecl(const Name &name, Type type, Expr *initExpr,
+               unsigned numConstraints)
+      : Base(name.getLoc(), &name), type(type), initExpr(initExpr),
+        numConstraints(numConstraints) {}
+
+  /// The type of the variable.
+  Type type;
+
+  /// The optional initializer expression of this statement.
+  Expr *initExpr;
+
+  /// The number of constraints attached to this variable.
+  unsigned numConstraints;
+
+  /// Allow access to various internals.
+  friend llvm::TrailingObjects<VariableDecl, ConstraintRef>;
+};
+
+//===----------------------------------------------------------------------===//
+// Module
+//===----------------------------------------------------------------------===//
+
+/// This class represents a top-level AST module.
+class Module final : public Node::NodeBase<Module, Node>,
+                     private llvm::TrailingObjects<Module, Decl *> {
+public:
+  static Module *create(Context &ctx, llvm::SMLoc loc,
+                        ArrayRef<Decl *> children);
+
+  /// Return the children of this module.
+  MutableArrayRef<Decl *> getChildren() {
+    return {getTrailingObjects<Decl *>(), numChildren};
+  }
+  ArrayRef<Decl *> getChildren() const {
+    return const_cast<Module *>(this)->getChildren();
+  }
+
+private:
+  Module(llvm::SMLoc loc, unsigned numChildren)
+      : Base(llvm::SMRange{loc, loc}), numChildren(numChildren) {}
+
+  /// The number of decls held by this module.
+  unsigned numChildren;
+
+  /// Allow access to various internals.
+  friend llvm::TrailingObjects<Module, Decl *>;
+};
+
+//===----------------------------------------------------------------------===//
+// Defered Method Definitions
+//===----------------------------------------------------------------------===//
+
+inline bool Decl::classof(const Node *node) {
+  return isa<ConstraintDecl, OpNameDecl, PatternDecl, VariableDecl>(node);
+}
+
+inline bool ConstraintDecl::classof(const Node *node) {
+  return isa<CoreConstraintDecl>(node);
+}
+
+inline bool CoreConstraintDecl::classof(const Node *node) {
+  return isa<AttrConstraintDecl, OpConstraintDecl, TypeConstraintDecl,
+             TypeRangeConstraintDecl, ValueConstraintDecl,
+             ValueRangeConstraintDecl>(node);
+}
+
+inline bool Expr::classof(const Node *node) {
+  return isa<DeclRefExpr, MemberAccessExpr>(node);
+}
+
+inline bool OpRewriteStmt::classof(const Node *node) {
+  return isa<EraseStmt>(node);
+}
+
+inline bool Stmt::classof(const Node *node) {
+  return isa<CompoundStmt, LetStmt, OpRewriteStmt, Expr>(node);
+}
+
+} // namespace ast
+} // namespace pdll
+} // namespace mlir
+
+#endif // MLIR_TOOLS_PDLL_AST_NODES_H_

mlir/include/mlir/Tools/PDLL/AST/Types.h

+//===- Types.h --------------------------------------------------*- 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_AST_TYPES_H_
+#define MLIR_TOOLS_PDLL_AST_TYPES_H_
+
+#include "mlir/Support/LLVM.h"
+#include "mlir/Support/StorageUniquer.h"
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+class Context;
+
+namespace detail {
+struct AttributeTypeStorage;
+struct ConstraintTypeStorage;
+struct OperationTypeStorage;
+struct RangeTypeStorage;
+struct TypeTypeStorage;
+struct ValueTypeStorage;
+} // namespace detail
+
+//===----------------------------------------------------------------------===//
+// Type
+//===----------------------------------------------------------------------===//
+
+class Type {
+public:
+  /// This class represents the internal storage of the Type class.
+  struct Storage;
+
+  /// This class provides several utilities when defining derived type classes.
+  template <typename ImplT, typename BaseT = Type>
+  class TypeBase : public BaseT {
+  public:
+    using Base = TypeBase<ImplT, BaseT>;
+    using ImplTy = ImplT;
+    using BaseT::BaseT;
+
+    /// Provide type casting support.
+    static bool classof(Type type) {
+      return type.getTypeID() == TypeID::get<ImplTy>();
+    }
+  };
+
+  Type(Storage *impl = nullptr) : impl(impl) {}
+  Type(const Type &other) = default;
+
+  bool operator==(const Type &other) const { return impl == other.impl; }
+  bool operator!=(const Type &other) const { return !(*this == other); }
+  explicit operator bool() const { return impl; }
+
+  /// Provide type casting support.
+  template <typename U>
+  bool isa() const {
+    assert(impl && "isa<> used on a null type.");
+    return U::classof(*this);
+  }
+  template <typename U, typename V, typename... Others>
+  bool isa() const {
+    return isa<U>() || isa<V, Others...>();
+  }
+  template <typename U>
+  U dyn_cast() const {
+    return isa<U>() ? U(impl) : U(nullptr);
+  }
+  template <typename U>
+  U dyn_cast_or_null() const {
+    return (impl && isa<U>()) ? U(impl) : U(nullptr);
+  }
+  template <typename U>
+  U cast() const {
+    assert(isa<U>());
+    return U(impl);
+  }
+
+  /// Return the internal storage instance of this type.
+  Storage *getImpl() const { return impl; }
+
+  /// Return the TypeID instance of this type.
+  TypeID getTypeID() const;
+
+  /// Print this type to the given stream.
+  void print(raw_ostream &os) const;
+
+  /// Try to refine this type with the one provided. Given two compatible types,
+  /// this will return a merged type contains as much detail from the two types.
+  /// For example, if refining two operation types and one contains a name,
+  /// while the other doesn't, the refined type contains the name. If the two
+  /// types are incompatible, null is returned.
+  Type refineWith(Type other) const;
+
+protected:
+  /// Return the internal storage instance of this type reinterpreted as the
+  /// given derived storage type.
+  template <typename T>
+  const T *getImplAs() const {
+    return static_cast<const T *>(impl);
+  }
+
+private:
+  Storage *impl;
+};
+
+inline llvm::hash_code hash_value(Type type) {
+  return DenseMapInfo<Type::Storage *>::getHashValue(type.getImpl());
+}
+
+inline raw_ostream &operator<<(raw_ostream &os, Type type) {
+  type.print(os);
+  return os;
+}
+
+//===----------------------------------------------------------------------===//
+// AttributeType
+//===----------------------------------------------------------------------===//
+
+/// This class represents a PDLL type that corresponds to an mlir::Attribute.
+class AttributeType : public Type::TypeBase<detail::AttributeTypeStorage> {
+public:
+  using Base::Base;
+
+  /// Return an instance of the Attribute type.
+  static AttributeType get(Context &context);
+};
+
+//===----------------------------------------------------------------------===//
+// ConstraintType
+//===----------------------------------------------------------------------===//
+
+/// This class represents a PDLL type that corresponds to a constraint. This
+/// type has no MLIR C++ API correspondance.
+class ConstraintType : public Type::TypeBase<detail::ConstraintTypeStorage> {
+public:
+  using Base::Base;
+
+  /// Return an instance of the Constraint type.
+  static ConstraintType get(Context &context);
+};
+
+//===----------------------------------------------------------------------===//
+// OperationType
+//===----------------------------------------------------------------------===//
+
+/// This class represents a PDLL type that corresponds to an mlir::Operation.
+class OperationType : public Type::TypeBase<detail::OperationTypeStorage> {
+public:
+  using Base::Base;
+
+  /// Return an instance of the Operation type with an optional operation name.
+  /// If no name is provided, this type may refer to any operation.
+  static OperationType get(Context &context,
+                           Optional<StringRef> name = llvm::None);
+
+  /// Return the name of this operation type, or None if it doesn't have on.
+  Optional<StringRef> getName() const;
+};
+
+//===----------------------------------------------------------------------===//
+// RangeType
+//===----------------------------------------------------------------------===//
+
+/// This class represents a PDLL type that corresponds to a range of elements
+/// with a given element type.
+class RangeType : public Type::TypeBase<detail::RangeTypeStorage> {
+public:
+  using Base::Base;
+
+  /// Return an instance of the Range type with the given element type.
+  static RangeType get(Context &context, Type elementType);
+
+  /// Return the element type of this range.
+  Type getElementType() const;
+};
+
+//===----------------------------------------------------------------------===//
+// TypeRangeType
+
+/// This class represents a PDLL type that corresponds to an mlir::TypeRange.
+class TypeRangeType : public RangeType {
+public:
+  using RangeType::RangeType;
+
+  /// Provide type casting support.
+  static bool classof(Type type);
+
+  /// Return an instance of the TypeRange type.
+  static TypeRangeType get(Context &context);
+};
+
+//===----------------------------------------------------------------------===//
+// ValueRangeType
+
+/// This class represents a PDLL type that corresponds to an mlir::ValueRange.
+class ValueRangeType : public RangeType {
+public:
+  using RangeType::RangeType;
+
+  /// Provide type casting support.
+  static bool classof(Type type);
+
+  /// Return an instance of the ValueRange type.
+  static ValueRangeType get(Context &context);
+};
+
+//===----------------------------------------------------------------------===//
+// TypeType
+//===----------------------------------------------------------------------===//
+
+/// This class represents a PDLL type that corresponds to an mlir::Type.
+class TypeType : public Type::TypeBase<detail::TypeTypeStorage> {
+public:
+  using Base::Base;
+
+  /// Return an instance of the Type type.
+  static TypeType get(Context &context);
+};
+
+//===----------------------------------------------------------------------===//
+// ValueType
+//===----------------------------------------------------------------------===//
+
+/// This class represents a PDLL type that corresponds to an mlir::Value.
+class ValueType : public Type::TypeBase<detail::ValueTypeStorage> {
+public:
+  using Base::Base;
+
+  /// Return an instance of the Value type.
+  static ValueType get(Context &context);
+};
+
+} // namespace ast
+} // namespace pdll
+} // namespace mlir
+
+namespace llvm {
+template <>
+struct DenseMapInfo<mlir::pdll::ast::Type> {
+  static mlir::pdll::ast::Type getEmptyKey() {
+    void *pointer = llvm::DenseMapInfo<void *>::getEmptyKey();
+    return mlir::pdll::ast::Type(
+        static_cast<mlir::pdll::ast::Type::Storage *>(pointer));
+  }
+  static mlir::pdll::ast::Type getTombstoneKey() {
+    void *pointer = llvm::DenseMapInfo<void *>::getTombstoneKey();
+    return mlir::pdll::ast::Type(
+        static_cast<mlir::pdll::ast::Type::Storage *>(pointer));
+  }
+  static unsigned getHashValue(mlir::pdll::ast::Type val) {
+    return llvm::hash_value(val.getImpl());
+  }
+  static bool isEqual(mlir::pdll::ast::Type lhs, mlir::pdll::ast::Type rhs) {
+    return lhs == rhs;
+  }
+};
+} // namespace llvm
+
+#endif // MLIR_TOOLS_PDLL_AST_TYPES_H_

mlir/include/mlir/Tools/PDLL/Parser/Parser.h

+//===- Parser.h - MLIR PDLL Frontend Parser ---------------------*- 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_PARSER_PARSER_H_
+#define MLIR_TOOLS_PDLL_PARSER_PARSER_H_
+
+#include <memory>
+
+#include "mlir/Support/LogicalResult.h"
+
+namespace llvm {
+class SourceMgr;
+} // namespace llvm
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+class Context;
+class Module;
+} // namespace ast
+
+/// Parse an AST module from the main file of the given source manager.
+FailureOr<ast::Module *>
+parsePDLAST(ast::Context &ctx, llvm::SourceMgr &sourceMgr,
+            const std::vector<std::string> &includeDirs);
+} // namespace pdll
+} // namespace mlir
+
+#endif // MLIR_TOOLS_PDLL_PARSER_PARSER_H_

mlir/lib/Tools/PDLL/AST/Context.cpp

+//===- Context.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/AST/Context.h"
+#include "TypeDetail.h"
+
+using namespace mlir;
+using namespace mlir::pdll::ast;
+
+Context::Context() {
+  typeUniquer.registerSingletonStorageType<detail::AttributeTypeStorage>();
+  typeUniquer.registerSingletonStorageType<detail::ConstraintTypeStorage>();
+  typeUniquer.registerSingletonStorageType<detail::TypeTypeStorage>();
+  typeUniquer.registerSingletonStorageType<detail::ValueTypeStorage>();
+
+  typeUniquer.registerParametricStorageType<detail::OperationTypeStorage>();
+  typeUniquer.registerParametricStorageType<detail::RangeTypeStorage>();
+}

mlir/lib/Tools/PDLL/AST/Diagnostic.cpp

+//===- Diagnostic.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/AST/Diagnostic.h"
+
+using namespace mlir;
+using namespace mlir::pdll::ast;
+
+//===----------------------------------------------------------------------===//
+// InFlightDiagnostic
+//===----------------------------------------------------------------------===//
+
+void InFlightDiagnostic::report() {
+  // If this diagnostic is still inflight and it hasn't been abandoned, then
+  // report it.
+  if (isInFlight()) {
+    owner->report(std::move(*impl));
+    owner = nullptr;
+  }
+  impl.reset();
+}

mlir/lib/Tools/PDLL/AST/NodePrinter.cpp

+//===- NodePrinter.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/AST/Context.h"
+#include "mlir/Tools/PDLL/AST/Nodes.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/TypeSwitch.h"
+#include "llvm/Support/SaveAndRestore.h"
+#include "llvm/Support/ScopedPrinter.h"
+
+using namespace mlir;
+using namespace mlir::pdll::ast;
+
+//===----------------------------------------------------------------------===//
+// NodePrinter
+//===----------------------------------------------------------------------===//
+
+namespace {
+class NodePrinter {
+public:
+  NodePrinter(raw_ostream &os) : os(os) {}
+
+  /// Print the given type to the stream.
+  void print(Type type);
+
+  /// Print the given node to the stream.
+  void print(const Node *node);
+
+private:
+  /// Print a range containing children of a node.
+  template <typename RangeT,
+            std::enable_if_t<!std::is_convertible<RangeT, const Node *>::value>
+                * = nullptr>
+  void printChildren(RangeT &&range) {
+    if (llvm::empty(range))
+      return;
+
+    // Print the first N-1 elements with a prefix of "|-".
+    auto it = std::begin(range);
+    for (unsigned i = 0, e = llvm::size(range) - 1; i < e; ++i, ++it)
+      print(*it);
+
+    // Print the last element.
+    elementIndentStack.back() = true;
+    print(*it);
+  }
+  template <typename RangeT, typename... OthersT,
+            std::enable_if_t<std::is_convertible<RangeT, const Node *>::value>
+                * = nullptr>
+  void printChildren(RangeT &&range, OthersT &&...others) {
+    printChildren(ArrayRef<const Node *>({range, others...}));
+  }
+  /// Print a range containing children of a node, nesting the children under
+  /// the given label.
+  template <typename RangeT>
+  void printChildren(StringRef label, RangeT &&range) {
+    if (llvm::empty(range))
+      return;
+    elementIndentStack.reserve(elementIndentStack.size() + 1);
+    llvm::SaveAndRestore<bool> lastElement(elementIndentStack.back(), true);
+
+    printIndent();
+    os << label << "`\n";
+    elementIndentStack.push_back(/*isLastElt*/ false);
+    printChildren(std::forward<RangeT>(range));
+    elementIndentStack.pop_back();
+  }
+
+  /// Print the given derived node to the stream.
+  void printImpl(const CompoundStmt *stmt);
+  void printImpl(const EraseStmt *stmt);
+  void printImpl(const LetStmt *stmt);
+
+  void printImpl(const DeclRefExpr *expr);
+  void printImpl(const MemberAccessExpr *expr);
+
+  void printImpl(const AttrConstraintDecl *decl);
+  void printImpl(const OpConstraintDecl *decl);
+  void printImpl(const TypeConstraintDecl *decl);
+  void printImpl(const TypeRangeConstraintDecl *decl);
+  void printImpl(const ValueConstraintDecl *decl);
+  void printImpl(const ValueRangeConstraintDecl *decl);
+  void printImpl(const OpNameDecl *decl);
+  void printImpl(const PatternDecl *decl);
+  void printImpl(const VariableDecl *decl);
+  void printImpl(const Module *module);
+
+  /// Print the current indent stack.
+  void printIndent() {
+    if (elementIndentStack.empty())
+      return;
+
+    for (bool isLastElt : llvm::makeArrayRef(elementIndentStack).drop_back())
+      os << (isLastElt ? "  " : " |");
+    os << (elementIndentStack.back() ? " `" : " |");
+  }
+
+  /// The raw output stream.
+  raw_ostream &os;
+
+  /// A stack of indents and a flag indicating if the current element being
+  /// printed at that indent is the last element.
+  SmallVector<bool> elementIndentStack;
+};
+} // namespace
+
+void NodePrinter::print(Type type) {
+  // Protect against invalid inputs.
+  if (!type) {
+    os << "Type<NULL>";
+    return;
+  }
+
+  TypeSwitch<Type>(type)
+      .Case([&](AttributeType) { os << "Attr"; })
+      .Case([&](ConstraintType) { os << "Constraint"; })
+      .Case([&](OperationType type) {
+        os << "Op";
+        if (Optional<StringRef> name = type.getName())
+          os << "<" << *name << ">";
+      })
+      .Case([&](RangeType type) {
+        print(type.getElementType());
+        os << "Range";
+      })
+      .Case([&](TypeType) { os << "Type"; })
+      .Case([&](ValueType) { os << "Value"; })
+      .Default([](Type) { llvm_unreachable("unknown AST type"); });
+}
+
+void NodePrinter::print(const Node *node) {
+  printIndent();
+  os << "-";
+
+  elementIndentStack.push_back(/*isLastElt*/ false);
+  TypeSwitch<const Node *>(node)
+      .Case<
+          // Statements.
+          const CompoundStmt, const EraseStmt, const LetStmt,
+
+          // Expressions.
+          const DeclRefExpr, const MemberAccessExpr,
+
+          // Decls.
+          const AttrConstraintDecl, const OpConstraintDecl,
+          const TypeConstraintDecl, const TypeRangeConstraintDecl,
+          const ValueConstraintDecl, const ValueRangeConstraintDecl,
+          const OpNameDecl, const PatternDecl, const VariableDecl,
+
+          const Module>([&](auto derivedNode) { this->printImpl(derivedNode); })
+      .Default([](const Node *) { llvm_unreachable("unknown AST node"); });
+  elementIndentStack.pop_back();
+}
+
+void NodePrinter::printImpl(const CompoundStmt *stmt) {
+  os << "CompoundStmt " << stmt << "\n";
+  printChildren(stmt->getChildren());
+}
+
+void NodePrinter::printImpl(const EraseStmt *stmt) {
+  os << "EraseStmt " << stmt << "\n";
+  printChildren(stmt->getRootOpExpr());
+}
+
+void NodePrinter::printImpl(const LetStmt *stmt) {
+  os << "LetStmt " << stmt << "\n";
+  printChildren(stmt->getVarDecl());
+}
+
+void NodePrinter::printImpl(const DeclRefExpr *expr) {
+  os << "DeclRefExpr " << expr << " Type<";
+  print(expr->getType());
+  os << ">\n";
+  printChildren(expr->getDecl());
+}
+
+void NodePrinter::printImpl(const MemberAccessExpr *expr) {
+  os << "MemberAccessExpr " << expr << " Member<" << expr->getMemberName()
+     << "> Type<";
+  print(expr->getType());
+  os << ">\n";
+  printChildren(expr->getParentExpr());
+}
+
+void NodePrinter::printImpl(const AttrConstraintDecl *decl) {
+  os << "AttrConstraintDecl " << decl << "\n";
+  if (const auto *typeExpr = decl->getTypeExpr())
+    printChildren(typeExpr);
+}
+
+void NodePrinter::printImpl(const OpConstraintDecl *decl) {
+  os << "OpConstraintDecl " << decl << "\n";
+  printChildren(decl->getNameDecl());
+}
+
+void NodePrinter::printImpl(const TypeConstraintDecl *decl) {
+  os << "TypeConstraintDecl " << decl << "\n";
+}
+
+void NodePrinter::printImpl(const TypeRangeConstraintDecl *decl) {
+  os << "TypeRangeConstraintDecl " << decl << "\n";
+}
+
+void NodePrinter::printImpl(const ValueConstraintDecl *decl) {
+  os << "ValueConstraintDecl " << decl << "\n";
+  if (const auto *typeExpr = decl->getTypeExpr())
+    printChildren(typeExpr);
+}
+
+void NodePrinter::printImpl(const ValueRangeConstraintDecl *decl) {
+  os << "ValueRangeConstraintDecl " << decl << "\n";
+  if (const auto *typeExpr = decl->getTypeExpr())
+    printChildren(typeExpr);
+}
+
+void NodePrinter::printImpl(const OpNameDecl *decl) {
+  os << "OpNameDecl " << decl;
+  if (Optional<StringRef> name = decl->getName())
+    os << " Name<" << name << ">";
+  os << "\n";
+}
+
+void NodePrinter::printImpl(const PatternDecl *decl) {
+  os << "PatternDecl " << decl;
+  if (const Name *name = decl->getName())
+    os << " Name<" << name->getName() << ">";
+  if (Optional<uint16_t> benefit = decl->getBenefit())
+    os << " Benefit<" << *benefit << ">";
+  if (decl->hasBoundedRewriteRecursion())
+    os << " Recursion";
+
+  os << "\n";
+  printChildren(decl->getBody());
+}
+
+void NodePrinter::printImpl(const VariableDecl *decl) {
+  os << "VariableDecl " << decl << " Name<" << decl->getName().getName()
+     << "> Type<";
+  print(decl->getType());
+  os << ">\n";
+  if (Expr *initExpr = decl->getInitExpr())
+    printChildren(initExpr);
+
+  auto constraints =
+      llvm::map_range(decl->getConstraints(),
+                      [](const ConstraintRef &ref) { return ref.constraint; });
+  printChildren("Constraints", constraints);
+}
+
+void NodePrinter::printImpl(const Module *module) {
+  os << "Module " << module << "\n";
+  printChildren(module->getChildren());
+}
+
+//===----------------------------------------------------------------------===//
+// Entry point
+//===----------------------------------------------------------------------===//
+
+void Node::print(raw_ostream &os) const { NodePrinter(os).print(this); }
+
+void Type::print(raw_ostream &os) const { NodePrinter(os).print(*this); }

mlir/lib/Tools/PDLL/AST/Nodes.cpp

+//===- Nodes.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/AST/Nodes.h"
+#include "mlir/Tools/PDLL/AST/Context.h"
+#include "llvm/ADT/SmallPtrSet.h"
+
+using namespace mlir;
+using namespace mlir::pdll::ast;
+
+/// Copy a string reference into the context with a null terminator.
+static StringRef copyStringWithNull(Context &ctx, StringRef str) {
+  if (str.empty())
+    return str;
+
+  char *data = ctx.getAllocator().Allocate<char>(str.size() + 1);
+  std::copy(str.begin(), str.end(), data);
+  data[str.size()] = 0;
+  return StringRef(data, str.size());
+}
+
+//===----------------------------------------------------------------------===//
+// Name
+//===----------------------------------------------------------------------===//
+
+const Name &Name::create(Context &ctx, StringRef name, llvm::SMRange location) {
+  return *new (ctx.getAllocator().Allocate<Name>())
+      Name(copyStringWithNull(ctx, name), location);
+}
+
+//===----------------------------------------------------------------------===//
+// DeclScope
+//===----------------------------------------------------------------------===//
+
+void DeclScope::add(Decl *decl) {
+  const Name *name = decl->getName();
+  assert(name && "expected a named decl");
+  assert(!decls.count(name->getName()) && "decl with this name already exists");
+  decls.try_emplace(name->getName(), decl);
+}
+
+Decl *DeclScope::lookup(StringRef name) {
+  if (Decl *decl = decls.lookup(name))
+    return decl;
+  return parent ? parent->lookup(name) : nullptr;
+}
+
+//===----------------------------------------------------------------------===//
+// CompoundStmt
+//===----------------------------------------------------------------------===//
+
+CompoundStmt *CompoundStmt::create(Context &ctx, llvm::SMRange loc,
+                                   ArrayRef<Stmt *> children) {
+  unsigned allocSize = CompoundStmt::totalSizeToAlloc<Stmt *>(children.size());
+  void *rawData = ctx.getAllocator().Allocate(allocSize, alignof(CompoundStmt));
+
+  CompoundStmt *stmt = new (rawData) CompoundStmt(loc, children.size());
+  std::uninitialized_copy(children.begin(), children.end(), stmt->begin());
+  return stmt;
+}
+
+//===----------------------------------------------------------------------===//
+// LetStmt
+//===----------------------------------------------------------------------===//
+
+LetStmt *LetStmt::create(Context &ctx, llvm::SMRange loc,
+                         VariableDecl *varDecl) {
+  return new (ctx.getAllocator().Allocate<LetStmt>()) LetStmt(loc, varDecl);
+}
+
+//===----------------------------------------------------------------------===//
+// OpRewriteStmt
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+// EraseStmt
+
+EraseStmt *EraseStmt::create(Context &ctx, llvm::SMRange loc, Expr *rootOp) {
+  return new (ctx.getAllocator().Allocate<EraseStmt>()) EraseStmt(loc, rootOp);
+}
+
+//===----------------------------------------------------------------------===//
+// DeclRefExpr
+//===----------------------------------------------------------------------===//
+
+DeclRefExpr *DeclRefExpr::create(Context &ctx, llvm::SMRange loc, Decl *decl,
+                                 Type type) {
+  return new (ctx.getAllocator().Allocate<DeclRefExpr>())
+      DeclRefExpr(loc, decl, type);
+}
+
+//===----------------------------------------------------------------------===//
+// MemberAccessExpr
+//===----------------------------------------------------------------------===//
+
+MemberAccessExpr *MemberAccessExpr::create(Context &ctx, llvm::SMRange loc,
+                                           const Expr *parentExpr,
+                                           StringRef memberName, Type type) {
+  return new (ctx.getAllocator().Allocate<MemberAccessExpr>()) MemberAccessExpr(
+      loc, parentExpr, memberName.copy(ctx.getAllocator()), type);
+}
+
+//===----------------------------------------------------------------------===//
+// AttrConstraintDecl
+//===----------------------------------------------------------------------===//
+
+AttrConstraintDecl *AttrConstraintDecl::create(Context &ctx, llvm::SMRange loc,
+                                               Expr *typeExpr) {
+  return new (ctx.getAllocator().Allocate<AttrConstraintDecl>())
+      AttrConstraintDecl(loc, typeExpr);
+}
+
+//===----------------------------------------------------------------------===//
+// OpConstraintDecl
+//===----------------------------------------------------------------------===//
+
+OpConstraintDecl *OpConstraintDecl::create(Context &ctx, llvm::SMRange loc,
+                                           const OpNameDecl *nameDecl) {
+  if (!nameDecl)
+    nameDecl = OpNameDecl::create(ctx, llvm::SMRange());
+
+  return new (ctx.getAllocator().Allocate<OpConstraintDecl>())
+      OpConstraintDecl(loc, nameDecl);
+}
+
+Optional<StringRef> OpConstraintDecl::getName() const {
+  return getNameDecl()->getName();
+}
+
+//===----------------------------------------------------------------------===//
+// TypeConstraintDecl
+//===----------------------------------------------------------------------===//
+
+TypeConstraintDecl *TypeConstraintDecl::create(Context &ctx,
+                                               llvm::SMRange loc) {
+  return new (ctx.getAllocator().Allocate<TypeConstraintDecl>())
+      TypeConstraintDecl(loc);
+}
+
+//===----------------------------------------------------------------------===//
+// TypeRangeConstraintDecl
+//===----------------------------------------------------------------------===//
+
+TypeRangeConstraintDecl *TypeRangeConstraintDecl::create(Context &ctx,
+                                                         llvm::SMRange loc) {
+  return new (ctx.getAllocator().Allocate<TypeRangeConstraintDecl>())
+      TypeRangeConstraintDecl(loc);
+}
+
+//===----------------------------------------------------------------------===//
+// ValueConstraintDecl
+//===----------------------------------------------------------------------===//
+
+ValueConstraintDecl *
+ValueConstraintDecl::create(Context &ctx, llvm::SMRange loc, Expr *typeExpr) {
+  return new (ctx.getAllocator().Allocate<ValueConstraintDecl>())
+      ValueConstraintDecl(loc, typeExpr);
+}
+
+//===----------------------------------------------------------------------===//
+// ValueRangeConstraintDecl
+//===----------------------------------------------------------------------===//
+
+ValueRangeConstraintDecl *ValueRangeConstraintDecl::create(Context &ctx,
+                                                           llvm::SMRange loc,
+                                                           Expr *typeExpr) {
+  return new (ctx.getAllocator().Allocate<ValueRangeConstraintDecl>())
+      ValueRangeConstraintDecl(loc, typeExpr);
+}
+
+//===----------------------------------------------------------------------===//
+// OpNameDecl
+//===----------------------------------------------------------------------===//
+
+OpNameDecl *OpNameDecl::create(Context &ctx, const Name &name) {
+  return new (ctx.getAllocator().Allocate<OpNameDecl>()) OpNameDecl(name);
+}
+OpNameDecl *OpNameDecl::create(Context &ctx, llvm::SMRange loc) {
+  return new (ctx.getAllocator().Allocate<OpNameDecl>()) OpNameDecl(loc);
+}
+
+//===----------------------------------------------------------------------===//
+// PatternDecl
+//===----------------------------------------------------------------------===//
+
+PatternDecl *PatternDecl::create(Context &ctx, llvm::SMRange loc,
+                                 const Name *name, Optional<uint16_t> benefit,
+                                 bool hasBoundedRecursion,
+                                 const CompoundStmt *body) {
+  return new (ctx.getAllocator().Allocate<PatternDecl>())
+      PatternDecl(loc, name, benefit, hasBoundedRecursion, body);
+}
+
+//===----------------------------------------------------------------------===//
+// VariableDecl
+//===----------------------------------------------------------------------===//
+
+VariableDecl *VariableDecl::create(Context &ctx, const Name &name, Type type,
+                                   Expr *initExpr,
+                                   ArrayRef<ConstraintRef> constraints) {
+  unsigned allocSize =
+      VariableDecl::totalSizeToAlloc<ConstraintRef>(constraints.size());
+  void *rawData = ctx.getAllocator().Allocate(allocSize, alignof(VariableDecl));
+
+  VariableDecl *varDecl =
+      new (rawData) VariableDecl(name, type, initExpr, constraints.size());
+  std::uninitialized_copy(constraints.begin(), constraints.end(),
+                          varDecl->getConstraints().begin());
+  return varDecl;
+}
+
+//===----------------------------------------------------------------------===//
+// Module
+//===----------------------------------------------------------------------===//
+
+Module *Module::create(Context &ctx, llvm::SMLoc loc,
+                       ArrayRef<Decl *> children) {
+  unsigned allocSize = Module::totalSizeToAlloc<Decl *>(children.size());
+  void *rawData = ctx.getAllocator().Allocate(allocSize, alignof(Module));
+
+  Module *module = new (rawData) Module(loc, children.size());
+  std::uninitialized_copy(children.begin(), children.end(),
+                          module->getChildren().begin());
+  return module;
+}

mlir/lib/Tools/PDLL/AST/TypeDetail.h

+//===- TypeDetail.h ---------------------------------------------*- 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 LIB_MLIR_TOOLS_PDLL_AST_TYPEDETAIL_H_
+#define LIB_MLIR_TOOLS_PDLL_AST_TYPEDETAIL_H_
+
+#include "mlir/Tools/PDLL/AST/Types.h"
+
+namespace mlir {
+namespace pdll {
+namespace ast {
+//===----------------------------------------------------------------------===//
+// Type
+//===----------------------------------------------------------------------===//
+
+struct Type::Storage : public StorageUniquer::BaseStorage {
+  Storage(TypeID typeID) : typeID(typeID) {}
+
+  /// The type identifier for the derived type class.
+  TypeID typeID;
+};
+
+namespace detail {
+
+/// A utility CRTP base class that defines many of the necessary utilities for
+/// defining a PDLL AST Type.
+template <typename ConcreteT, typename KeyT = void>
+struct TypeStorageBase : public Type::Storage {
+  using KeyTy = KeyT;
+  using Base = TypeStorageBase<ConcreteT, KeyT>;
+
+  /// Construct an instance with the given storage allocator.
+  static ConcreteT *construct(StorageUniquer::StorageAllocator &alloc,
+                              const KeyTy &key) {
+    return new (alloc.allocate<ConcreteT>()) ConcreteT(key);
+  }
+
+  /// Utility methods required by the storage allocator.
+  bool operator==(const KeyTy &key) const { return this->key == key; }
+
+  /// Return the key value of this storage class.
+  const KeyTy &getValue() const { return key; }
+
+protected:
+  TypeStorageBase(KeyTy key)
+      : Type::Storage(TypeID::get<ConcreteT>()), key(key) {}
+
+  KeyTy key;
+};
+/// A specialization of the storage base for singleton types.
+template <typename ConcreteT>
+struct TypeStorageBase<ConcreteT, void> : public Type::Storage {
+  using Base = TypeStorageBase<ConcreteT, void>;
+
+protected:
+  TypeStorageBase() : Type::Storage(TypeID::get<ConcreteT>()) {}
+};
+
+//===----------------------------------------------------------------------===//
+// AttributeType
+//===----------------------------------------------------------------------===//
+
+struct AttributeTypeStorage : public TypeStorageBase<AttributeTypeStorage> {};
+
+//===----------------------------------------------------------------------===//
+// ConstraintType
+//===----------------------------------------------------------------------===//
+
+struct ConstraintTypeStorage : public TypeStorageBase<ConstraintTypeStorage> {};
+
+//===----------------------------------------------------------------------===//
+// OperationType
+//===----------------------------------------------------------------------===//
+
+struct OperationTypeStorage
+    : public TypeStorageBase<OperationTypeStorage, StringRef> {
+  using Base::Base;
+
+  static OperationTypeStorage *
+  construct(StorageUniquer::StorageAllocator &alloc, StringRef key) {
+    return new (alloc.allocate<OperationTypeStorage>())
+        OperationTypeStorage(alloc.copyInto(key));
+  }
+};
+
+//===----------------------------------------------------------------------===//
+// RangeType
+//===----------------------------------------------------------------------===//
+
+struct RangeTypeStorage : public TypeStorageBase<RangeTypeStorage, Type> {
+  using Base::Base;
+};
+
+//===----------------------------------------------------------------------===//
+// TypeType
+//===----------------------------------------------------------------------===//
+
+struct TypeTypeStorage : public TypeStorageBase<TypeTypeStorage> {};
+
+//===----------------------------------------------------------------------===//
+// ValueType
+//===----------------------------------------------------------------------===//
+
+struct ValueTypeStorage : public TypeStorageBase<ValueTypeStorage> {};
+
+} // namespace detail
+} // namespace ast
+} // namespace pdll
+} // namespace mlir
+
+#endif // LIB_MLIR_TOOLS_PDLL_AST_TYPEDETAIL_H_

mlir/lib/Tools/PDLL/AST/Types.cpp

+//===- Types.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/AST/Types.h"
+#include "TypeDetail.h"
+#include "mlir/Tools/PDLL/AST/Context.h"
+
+using namespace mlir;
+using namespace mlir::pdll::ast;
+
+//===----------------------------------------------------------------------===//
+// Type
+//===----------------------------------------------------------------------===//
+
+TypeID Type::getTypeID() const { return impl->typeID; }
+
+Type Type::refineWith(Type other) const {
+  if (*this == other)
+    return *this;
+
+  // Operation types are compatible if the operation names don't conflict.
+  if (auto opTy = dyn_cast<OperationType>()) {
+    auto otherOpTy = other.dyn_cast<ast::OperationType>();
+    if (!otherOpTy)
+      return nullptr;
+    if (!otherOpTy.getName())
+      return *this;
+    if (!opTy.getName())
+      return other;
+
+    return nullptr;
+  }
+
+  return nullptr;
+}
+
+//===----------------------------------------------------------------------===//
+// AttributeType
+//===----------------------------------------------------------------------===//
+
+AttributeType AttributeType::get(Context &context) {
+  return context.getTypeUniquer().get<ImplTy>();
+}
+
+//===----------------------------------------------------------------------===//
+// ConstraintType
+//===----------------------------------------------------------------------===//
+
+ConstraintType ConstraintType::get(Context &context) {
+  return context.getTypeUniquer().get<ImplTy>();
+}
+
+//===----------------------------------------------------------------------===//
+// OperationType
+//===----------------------------------------------------------------------===//
+
+OperationType OperationType::get(Context &context, Optional<StringRef> name) {
+  return context.getTypeUniquer().get<ImplTy>(
+      /*initFn=*/function_ref<void(ImplTy *)>(), name.getValueOr(""));
+}
+
+Optional<StringRef> OperationType::getName() const {
+  StringRef name = getImplAs<ImplTy>()->getValue();
+  return name.empty() ? Optional<StringRef>() : Optional<StringRef>(name);
+}
+
+//===----------------------------------------------------------------------===//
+// RangeType
+//===----------------------------------------------------------------------===//
+
+RangeType RangeType::get(Context &context, Type elementType) {
+  return context.getTypeUniquer().get<ImplTy>(
+      /*initFn=*/function_ref<void(ImplTy *)>(), elementType);
+}
+
+Type RangeType::getElementType() const {
+  return getImplAs<ImplTy>()->getValue();
+}
+
+//===----------------------------------------------------------------------===//
+// TypeRangeType
+
+bool TypeRangeType::classof(Type type) {
+  RangeType range = type.dyn_cast<RangeType>();
+  return range && range.getElementType().isa<TypeType>();
+}
+
+TypeRangeType TypeRangeType::get(Context &context) {
+  return RangeType::get(context, TypeType::get(context)).cast<TypeRangeType>();
+}
+
+//===----------------------------------------------------------------------===//
+// ValueRangeType
+
+bool ValueRangeType::classof(Type type) {
+  RangeType range = type.dyn_cast<RangeType>();
+  return range && range.getElementType().isa<ValueType>();
+}
+
+ValueRangeType ValueRangeType::get(Context &context) {
+  return RangeType::get(context, ValueType::get(context))
+      .cast<ValueRangeType>();
+}
+
+//===----------------------------------------------------------------------===//
+// TypeType
+//===----------------------------------------------------------------------===//
+
+TypeType TypeType::get(Context &context) {
+  return context.getTypeUniquer().get<ImplTy>();
+}
+
+//===----------------------------------------------------------------------===//
+// ValueType
+//===----------------------------------------------------------------------===//
+
+ValueType ValueType::get(Context &context) {
+  return context.getTypeUniquer().get<ImplTy>();
+}

mlir/lib/Tools/PDLL/Parser/Lexer.h

+//===- Lexer.h - MLIR PDLL Frontend Lexer -----------------------*- 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 LIB_TOOLS_PDLL_PARSER_LEXER_H_
+#define LIB_TOOLS_PDLL_PARSER_LEXER_H_
+
+#include "mlir/Support/LLVM.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/SMLoc.h"
+
+namespace llvm {
+class SourceMgr;
+} // namespace llvm
+
+namespace mlir {
+struct LogicalResult;
+
+namespace pdll {
+namespace ast {
+class DiagnosticEngine;
+} // namespace ast
+
+//===----------------------------------------------------------------------===//
+// Token
+//===----------------------------------------------------------------------===//
+
+class Token {
+public:
+  enum Kind {
+    // Markers.
+    eof,
+    error,
+
+    // Keywords.
+    KW_BEGIN,
+    // Dependent keywords, i.e. those that are treated as keywords depending on
+    // the current parser context.
+    KW_DEPENDENT_BEGIN,
+    kw_attr,
+    kw_op,
+    kw_type,
+    KW_DEPENDENT_END,
+
+    // General keywords.
+    kw_Attr,
+    kw_erase,
+    kw_let,
+    kw_Constraint,
+    kw_Op,
+    kw_OpName,
+    kw_Pattern,
+    kw_replace,
+    kw_rewrite,
+    kw_Type,
+    kw_TypeRange,
+    kw_Value,
+    kw_ValueRange,
+    kw_with,
+    KW_END,
+
+    // Punctuation.
+    arrow,
+    colon,
+    comma,
+    dot,
+    equal,
+    equal_arrow,
+    semicolon,
+    // Paired punctuation.
+    less,
+    greater,
+    l_brace,
+    r_brace,
+    l_paren,
+    r_paren,
+    l_square,
+    r_square,
+    underscore,
+
+    // Tokens.
+    directive,
+    identifier,
+    integer,
+    string_block,
+    string
+  };
+  Token(Kind kind, StringRef spelling) : kind(kind), spelling(spelling) {}
+
+  /// Given a token containing a string literal, return its value, including
+  /// removing the quote characters and unescaping the contents of the string.
+  std::string getStringValue() const;
+
+  /// Returns true if the current token is a string literal.
+  bool isString() const { return isAny(Token::string, Token::string_block); }
+
+  /// Returns true if the current token is a keyword.
+  bool isKeyword() const {
+    return kind > Token::KW_BEGIN && kind < Token::KW_END;
+  }
+
+  /// Returns true if the current token is a keyword in a dependent context, and
+  /// in any other situation (e.g. variable names) may be treated as an
+  /// identifier.
+  bool isDependentKeyword() const {
+    return kind > Token::KW_DEPENDENT_BEGIN && kind < Token::KW_DEPENDENT_END;
+  }
+
+  /// Return the bytes that make up this token.
+  StringRef getSpelling() const { return spelling; }
+
+  /// Return the kind of this token.
+  Kind getKind() const { return kind; }
+
+  /// Return true if this token is one of the specified kinds.
+  bool isAny(Kind k1, Kind k2) const { return is(k1) || is(k2); }
+  template <typename... T>
+  bool isAny(Kind k1, Kind k2, Kind k3, T... others) const {
+    return is(k1) || isAny(k2, k3, others...);
+  }
+
+  /// Return if the token does not have the given kind.
+  bool isNot(Kind k) const { return k != kind; }
+  template <typename... T>
+  bool isNot(Kind k1, Kind k2, T... others) const {
+    return !isAny(k1, k2, others...);
+  }
+
+  /// Return if the token has the given kind.
+  bool is(Kind K) const { return kind == K; }
+
+  /// Return a location for the start of this token.
+  llvm::SMLoc getStartLoc() const {
+    return llvm::SMLoc::getFromPointer(spelling.data());
+  }
+  /// Return a location at the end of this token.
+  llvm::SMLoc getEndLoc() const {
+    return llvm::SMLoc::getFromPointer(spelling.data() + spelling.size());
+  }
+  /// Return a location for the range of this token.
+  llvm::SMRange getLoc() const {
+    return llvm::SMRange(getStartLoc(), getEndLoc());
+  }
+
+private:
+  /// Discriminator that indicates the kind of token this is.
+  Kind kind;
+
+  /// A reference to the entire token contents; this is always a pointer into
+  /// a memory buffer owned by the source manager.
+  StringRef spelling;
+};
+
+//===----------------------------------------------------------------------===//
+// Lexer
+//===----------------------------------------------------------------------===//
+
+class Lexer {
+public:
+  Lexer(llvm::SourceMgr &mgr, ast::DiagnosticEngine &diagEngine);
+  ~Lexer();
+
+  /// Return a reference to the source manager used by the lexer.
+  llvm::SourceMgr &getSourceMgr() { return srcMgr; }
+
+  /// Return a reference to the diagnostic engine used by the lexer.
+  ast::DiagnosticEngine &getDiagEngine() { return diagEngine; }
+
+  /// Push an include of the given file. This will cause the lexer to start
+  /// processing the provided file. Returns failure if the file could not be
+  /// opened, success otherwise.
+  LogicalResult pushInclude(StringRef filename);
+
+  /// Lex the next token and return it.
+  Token lexToken();
+
+  /// Change the position of the lexer cursor. The next token we lex will start
+  /// at the designated point in the input.
+  void resetPointer(const char *newPointer) { curPtr = newPointer; }
+
+  /// Emit an error to the lexer with the given location and message.
+  Token emitError(llvm::SMRange loc, const Twine &msg);
+  Token emitError(const char *loc, const Twine &msg);
+  Token emitErrorAndNote(llvm::SMRange loc, const Twine &msg,
+                         llvm::SMRange noteLoc, const Twine &note);
+
+private:
+  Token formToken(Token::Kind kind, const char *tokStart) {
+    return Token(kind, StringRef(tokStart, curPtr - tokStart));
+  }
+
+  /// Return the next character in the stream.
+  int getNextChar();
+
+  /// Lex methods.
+  void lexComment();
+  Token lexDirective(const char *tokStart);
+  Token lexIdentifier(const char *tokStart);
+  Token lexNumber(const char *tokStart);
+  Token lexString(const char *tokStart, bool isStringBlock);
+
+  llvm::SourceMgr &srcMgr;
+  int curBufferID;
+  StringRef curBuffer;
+  const char *curPtr;
+
+  /// The engine used to emit diagnostics during lexing/parsing.
+  ast::DiagnosticEngine &diagEngine;
+
+  /// A flag indicating if we added a default diagnostic handler to the provided
+  /// diagEngine.
+  bool addedHandlerToDiagEngine;
+};
+} // namespace pdll
+} // namespace mlir
+
+#endif // LIB_TOOLS_PDLL_PARSER_LEXER_H_

mlir/lib/Tools/PDLL/Parser/Lexer.cpp

+//===- Lexer.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 "Lexer.h"
+#include "mlir/Support/LogicalResult.h"
+#include "mlir/Tools/PDLL/AST/Diagnostic.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/SourceMgr.h"
+
+using namespace mlir;
+using namespace mlir::pdll;
+
+//===----------------------------------------------------------------------===//
+// Token
+//===----------------------------------------------------------------------===//
+
+std::string Token::getStringValue() const {
+  assert(getKind() == string || getKind() == string_block);
+
+  // Start by dropping the quotes.
+  StringRef bytes = getSpelling().drop_front().drop_back();
+  if (is(string_block))
+    bytes = bytes.drop_front().drop_back();
+
+  std::string result;
+  result.reserve(bytes.size());
+  for (unsigned i = 0, e = bytes.size(); i != e;) {
+    auto c = bytes[i++];
+    if (c != '\\') {
+      result.push_back(c);
+      continue;
+    }
+
+    assert(i + 1 <= e && "invalid string should be caught by lexer");
+    auto c1 = bytes[i++];
+    switch (c1) {
+    case '"':
+    case '\\':
+      result.push_back(c1);
+      continue;
+    case 'n':
+      result.push_back('\n');
+      continue;
+    case 't':
+      result.push_back('\t');
+      continue;
+    default:
+      break;
+    }
+
+    assert(i + 1 <= e && "invalid string should be caught by lexer");
+    auto c2 = bytes[i++];
+
+    assert(llvm::isHexDigit(c1) && llvm::isHexDigit(c2) && "invalid escape");
+    result.push_back((llvm::hexDigitValue(c1) << 4) | llvm::hexDigitValue(c2));
+  }
+
+  return result;
+}
+
+//===----------------------------------------------------------------------===//
+// Lexer
+//===----------------------------------------------------------------------===//
+
+Lexer::Lexer(llvm::SourceMgr &mgr, ast::DiagnosticEngine &diagEngine)
+    : srcMgr(mgr), diagEngine(diagEngine), addedHandlerToDiagEngine(false) {
+  curBufferID = mgr.getMainFileID();
+  curBuffer = srcMgr.getMemoryBuffer(curBufferID)->getBuffer();
+  curPtr = curBuffer.begin();
+
+  // If the diag engine has no handler, add a default that emits to the
+  // SourceMgr.
+  if (!diagEngine.getHandlerFn()) {
+    diagEngine.setHandlerFn([&](const ast::Diagnostic &diag) {
+      srcMgr.PrintMessage(diag.getLocation().Start, diag.getSeverity(),
+                          diag.getMessage());
+      for (const ast::Diagnostic &note : diag.getNotes())
+        srcMgr.PrintMessage(note.getLocation().Start, note.getSeverity(),
+                            note.getMessage());
+    });
+    addedHandlerToDiagEngine = true;
+  }
+}
+
+Lexer::~Lexer() {
+  if (addedHandlerToDiagEngine)
+    diagEngine.setHandlerFn(nullptr);
+}
+
+LogicalResult Lexer::pushInclude(StringRef filename) {
+  std::string includedFile;
+  int bufferID = srcMgr.AddIncludeFile(
+      filename.str(), llvm::SMLoc::getFromPointer(curPtr), includedFile);
+  if (!bufferID)
+    return failure();
+
+  curBufferID = bufferID;
+  curBuffer = srcMgr.getMemoryBuffer(curBufferID)->getBuffer();
+  curPtr = curBuffer.begin();
+  return success();
+}
+
+Token Lexer::emitError(llvm::SMRange loc, const Twine &msg) {
+  diagEngine.emitError(loc, msg);
+  return formToken(Token::error, loc.Start.getPointer());
+}
+Token Lexer::emitErrorAndNote(llvm::SMRange loc, const Twine &msg,
+                              llvm::SMRange noteLoc, const Twine &note) {
+  diagEngine.emitError(loc, msg)->attachNote(note, noteLoc);
+  return formToken(Token::error, loc.Start.getPointer());
+}
+Token Lexer::emitError(const char *loc, const Twine &msg) {
+  return emitError(llvm::SMRange(llvm::SMLoc::getFromPointer(loc),
+                                 llvm::SMLoc::getFromPointer(loc + 1)),
+                   msg);
+}
+
+int Lexer::getNextChar() {
+  char curChar = *curPtr++;
+  switch (curChar) {
+  default:
+    return static_cast<unsigned char>(curChar);
+  case 0: {
+    // A nul character in the stream is either the end of the current buffer
+    // or a random nul in the file. Disambiguate that here.
+    if (curPtr - 1 != curBuffer.end())
+      return 0;
+
+    // Otherwise, return end of file.
+    --curPtr;
+    return EOF;
+  }
+  case '\n':
+  case '\r':
+    // Handle the newline character by ignoring it and incrementing the line
+    // count. However, be careful about 'dos style' files with \n\r in them.
+    // Only treat a \n\r or \r\n as a single line.
+    if ((*curPtr == '\n' || (*curPtr == '\r')) && *curPtr != curChar)
+      ++curPtr;
+    return '\n';
+  }
+}
+
+Token Lexer::lexToken() {
+  while (true) {
+    const char *tokStart = curPtr;
+
+    // This always consumes at least one character.
+    int curChar = getNextChar();
+    switch (curChar) {
+    default:
+      // Handle identifiers: [a-zA-Z_]
+      if (isalpha(curChar) || curChar == '_')
+        return lexIdentifier(tokStart);
+
+      // Unknown character, emit an error.
+      return emitError(tokStart, "unexpected character");
+    case EOF: {
+      // Return EOF denoting the end of lexing.
+      Token eof = formToken(Token::eof, tokStart);
+
+      // Check to see if we are in an included file.
+      llvm::SMLoc parentIncludeLoc = srcMgr.getParentIncludeLoc(curBufferID);
+      if (parentIncludeLoc.isValid()) {
+        curBufferID = srcMgr.FindBufferContainingLoc(parentIncludeLoc);
+        curBuffer = srcMgr.getMemoryBuffer(curBufferID)->getBuffer();
+        curPtr = parentIncludeLoc.getPointer();
+      }
+
+      return eof;
+    }
+
+    // Lex punctuation.
+    case '-':
+      if (*curPtr == '>') {
+        ++curPtr;
+        return formToken(Token::arrow, tokStart);
+      }
+      return emitError(tokStart, "unexpected character");
+    case ':':
+      return formToken(Token::colon, tokStart);
+    case ',':
+      return formToken(Token::comma, tokStart);
+    case '.':
+      return formToken(Token::dot, tokStart);
+    case '=':
+      if (*curPtr == '>') {
+        ++curPtr;
+        return formToken(Token::equal_arrow, tokStart);
+      }
+      return formToken(Token::equal, tokStart);
+    case ';':
+      return formToken(Token::semicolon, tokStart);
+    case '[':
+      if (*curPtr == '{') {
+        ++curPtr;
+        return lexString(tokStart, /*isStringBlock=*/true);
+      }
+      return formToken(Token::l_square, tokStart);
+    case ']':
+      return formToken(Token::r_square, tokStart);
+
+    case '<':
+      return formToken(Token::less, tokStart);
+    case '>':
+      return formToken(Token::greater, tokStart);
+    case '{':
+      return formToken(Token::l_brace, tokStart);
+    case '}':
+      return formToken(Token::r_brace, tokStart);
+    case '(':
+      return formToken(Token::l_paren, tokStart);
+    case ')':
+      return formToken(Token::r_paren, tokStart);
+    case '/':
+      if (*curPtr == '/') {
+        lexComment();
+        continue;
+      }
+      return emitError(tokStart, "unexpected character");
+
+    // Ignore whitespace characters.
+    case 0:
+    case ' ':
+    case '\t':
+    case '\n':
+      return lexToken();
+
+    case '#':
+      return lexDirective(tokStart);
+    case '"':
+      return lexString(tokStart, /*isStringBlock=*/false);
+
+    case '0':
+    case '1':
+    case '2':
+    case '3':
+    case '4':
+    case '5':
+    case '6':
+    case '7':
+    case '8':
+    case '9':
+      return lexNumber(tokStart);
+    }
+  }
+}
+
+/// Skip a comment line, starting with a '//'.
+void Lexer::lexComment() {
+  // Advance over the second '/' in a '//' comment.
+  assert(*curPtr == '/');
+  ++curPtr;
+
+  while (true) {
+    switch (*curPtr++) {
+    case '\n':
+    case '\r':
+      // Newline is end of comment.
+      return;
+    case 0:
+      // If this is the end of the buffer, end the comment.
+      if (curPtr - 1 == curBuffer.end()) {
+        --curPtr;
+        return;
+      }
+      LLVM_FALLTHROUGH;
+    default:
+      // Skip over other characters.
+      break;
+    }
+  }
+}
+
+Token Lexer::lexDirective(const char *tokStart) {
+  // Match the rest with an identifier regex: [0-9a-zA-Z_]*
+  while (isalnum(*curPtr) || *curPtr == '_')
+    ++curPtr;
+
+  StringRef str(tokStart, curPtr - tokStart);
+  return Token(Token::directive, str);
+}
+
+Token Lexer::lexIdentifier(const char *tokStart) {
+  // Match the rest of the identifier regex: [0-9a-zA-Z_]*
+  while (isalnum(*curPtr) || *curPtr == '_')
+    ++curPtr;
+
+  // Check to see if this identifier is a keyword.
+  StringRef str(tokStart, curPtr - tokStart);
+  Token::Kind kind = StringSwitch<Token::Kind>(str)
+                         .Case("attr", Token::kw_attr)
+                         .Case("Attr", Token::kw_Attr)
+                         .Case("erase", Token::kw_erase)
+                         .Case("let", Token::kw_let)
+                         .Case("Constraint", Token::kw_Constraint)
+                         .Case("op", Token::kw_op)
+                         .Case("Op", Token::kw_Op)
+                         .Case("OpName", Token::kw_OpName)
+                         .Case("Pattern", Token::kw_Pattern)
+                         .Case("replace", Token::kw_replace)
+                         .Case("rewrite", Token::kw_rewrite)
+                         .Case("type", Token::kw_type)
+                         .Case("Type", Token::kw_Type)
+                         .Case("TypeRange", Token::kw_TypeRange)
+                         .Case("Value", Token::kw_Value)
+                         .Case("ValueRange", Token::kw_ValueRange)
+                         .Case("with", Token::kw_with)
+                         .Case("_", Token::underscore)
+                         .Default(Token::identifier);
+  return Token(kind, str);
+}
+
+Token Lexer::lexNumber(const char *tokStart) {
+  assert(isdigit(curPtr[-1]));
+
+  // Handle the normal decimal case.
+  while (isdigit(*curPtr))
+    ++curPtr;
+
+  return formToken(Token::integer, tokStart);
+}
+
+Token Lexer::lexString(const char *tokStart, bool isStringBlock) {
+  while (true) {
+    switch (*curPtr++) {
+    case '"':
+      // If this is a string block, we only end the string when we encounter a
+      // `}]`.
+      if (!isStringBlock)
+        return formToken(Token::string, tokStart);
+      continue;
+    case '}':
+      // If this is a string block, we only end the string when we encounter a
+      // `}]`.
+      if (!isStringBlock || *curPtr != ']')
+        continue;
+      ++curPtr;
+      return formToken(Token::string_block, tokStart);
+    case 0:
+      // If this is a random nul character in the middle of a string, just
+      // include it.  If it is the end of file, then it is an error.
+      if (curPtr - 1 != curBuffer.end())
+        continue;
+      LLVM_FALLTHROUGH;
+    case '\n':
+    case '\v':
+    case '\f':
+      // String blocks allow multiple lines.
+      if (!isStringBlock)
+        return emitError(curPtr - 1, "expected '\"' in string literal");
+      continue;
+
+    case '\\':
+      // Handle explicitly a few escapes.
+      if (*curPtr == '"' || *curPtr == '\\' || *curPtr == 'n' ||
+          *curPtr == 't') {
+        ++curPtr;
+      } else if (llvm::isHexDigit(*curPtr) && llvm::isHexDigit(curPtr[1])) {
+        // Support \xx for two hex digits.
+        curPtr += 2;
+      } else {
+        return emitError(curPtr - 1, "unknown escape in string literal");
+      }
+      continue;
+
+    default:
+      continue;
+    }
+  }
+}

mlir/lib/Tools/PDLL/Parser/Parser.cpp

+//===- Parser.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/Parser/Parser.h"
+#include "Lexer.h"
+#include "mlir/Support/LogicalResult.h"
+#include "mlir/Tools/PDLL/AST/Context.h"
+#include "mlir/Tools/PDLL/AST/Diagnostic.h"
+#include "mlir/Tools/PDLL/AST/Nodes.h"
+#include "mlir/Tools/PDLL/AST/Types.h"
+#include "llvm/ADT/TypeSwitch.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/SaveAndRestore.h"
+#include <string>
+
+using namespace mlir;
+using namespace mlir::pdll;
+
+//===----------------------------------------------------------------------===//
+// Parser
+//===----------------------------------------------------------------------===//
+
+namespace {
+class Parser {
+public:
+  Parser(ast::Context &ctx, llvm::SourceMgr &sourceMgr,
+         const std::vector<std::string> &includeDirs)
+      : ctx(ctx), lexer(sourceMgr, ctx.getDiagEngine()),
+        curToken(lexer.lexToken()), curDeclScope(nullptr),
+        includeDirs(includeDirs), valueTy(ast::ValueType::get(ctx)),
+        valueRangeTy(ast::ValueRangeType::get(ctx)),
+        typeTy(ast::TypeType::get(ctx)),
+        typeRangeTy(ast::TypeRangeType::get(ctx)) {}
+
+  /// Try to parse a new module. Returns nullptr in the case of failure.
+  FailureOr<ast::Module *> parseModule();
+
+private:
+  /// The current context of the parser. It allows for the parser to know a bit
+  /// about the construct it is nested within during parsing. This is used
+  /// specifically to provide additional verification during parsing, e.g. to
+  /// prevent using rewrites within a match context, matcher constraints within
+  /// a rewrite section, etc.
+  enum class ParserContext {
+    /// The parser is in the global context.
+    Global,
+    /// The parser is currently within the matcher portion of a Pattern, which
+    /// is allows a terminal operation rewrite statement but no other rewrite
+    /// transformations.
+    PatternMatch,
+  };
+
+  //===--------------------------------------------------------------------===//
+  // Parsing
+  //===--------------------------------------------------------------------===//
+
+  /// Push a new decl scope onto the lexer.
+  ast::DeclScope *pushDeclScope() {
+    ast::DeclScope *newScope =
+        new (scopeAllocator.Allocate()) ast::DeclScope(curDeclScope);
+    return (curDeclScope = newScope);
+  }
+  void pushDeclScope(ast::DeclScope *scope) { curDeclScope = scope; }
+
+  /// Pop the last decl scope from the lexer.
+  void popDeclScope() { curDeclScope = curDeclScope->getParentScope(); }
+
+  /// Parse the body of an AST module.
+  LogicalResult parseModuleBody(SmallVector<ast::Decl *> &decls);
+
+  /// Try to convert the given expression to `type`. Returns failure and emits
+  /// an error if a conversion is not viable. On failure, `noteAttachFn` is
+  /// invoked to attach notes to the emitted error diagnostic. On success,
+  /// `expr` is updated to the expression used to convert to `type`.
+  LogicalResult convertExpressionTo(
+      ast::Expr *&expr, ast::Type type,
+      function_ref<void(ast::Diagnostic &diag)> noteAttachFn = {});
+
+  //===--------------------------------------------------------------------===//
+  // Directives
+
+  LogicalResult parseDirective(SmallVector<ast::Decl *> &decls);
+  LogicalResult parseInclude(SmallVector<ast::Decl *> &decls);
+
+  //===--------------------------------------------------------------------===//
+  // Decls
+
+  FailureOr<ast::Decl *> parseTopLevelDecl();
+  FailureOr<ast::Decl *> parsePatternDecl();
+
+  /// Check to see if a decl has already been defined with the given name, if
+  /// one has emit and error and return failure. Returns success otherwise.
+  LogicalResult checkDefineNamedDecl(const ast::Name &name);
+
+  /// Try to define a variable decl with the given components, returns the
+  /// variable on success.
+  FailureOr<ast::VariableDecl *>
+  defineVariableDecl(StringRef name, llvm::SMRange nameLoc, ast::Type type,
+                     ast::Expr *initExpr,
+                     ArrayRef<ast::ConstraintRef> constraints);
+  FailureOr<ast::VariableDecl *>
+  defineVariableDecl(StringRef name, llvm::SMRange nameLoc, ast::Type type,
+                     ArrayRef<ast::ConstraintRef> constraints);
+
+  /// Parse the constraint reference list for a variable decl.
+  LogicalResult parseVariableDeclConstraintList(
+      SmallVectorImpl<ast::ConstraintRef> &constraints);
+
+  /// Parse the expression used within a type constraint, e.g. Attr<type-expr>.
+  FailureOr<ast::Expr *> parseTypeConstraintExpr();
+
+  /// Try to parse a single reference to a constraint. `typeConstraint` is the
+  /// location of a previously parsed type constraint for the entity that will
+  /// be constrained by the parsed constraint. `existingConstraints` are any
+  /// existing constraints that have already been parsed for the same entity
+  /// that will be constrained by this constraint.
+  FailureOr<ast::ConstraintRef>
+  parseConstraint(Optional<llvm::SMRange> &typeConstraint,
+                  ArrayRef<ast::ConstraintRef> existingConstraints);
+
+  //===--------------------------------------------------------------------===//
+  // Exprs
+
+  FailureOr<ast::Expr *> parseExpr();
+
+  /// Identifier expressions.
+  FailureOr<ast::Expr *> parseDeclRefExpr(StringRef name, llvm::SMRange loc);
+  FailureOr<ast::Expr *> parseIdentifierExpr();
+  FailureOr<ast::Expr *> parseMemberAccessExpr(ast::Expr *parentExpr);
+  FailureOr<ast::OpNameDecl *> parseOperationName();
+  FailureOr<ast::OpNameDecl *> parseWrappedOperationName();
+  FailureOr<ast::Expr *> parseUnderscoreExpr();
+
+  //===--------------------------------------------------------------------===//
+  // Stmts
+
+  FailureOr<ast::Stmt *> parseStmt(bool expectTerminalSemicolon = true);
+  FailureOr<ast::CompoundStmt *> parseCompoundStmt();
+  FailureOr<ast::EraseStmt *> parseEraseStmt();
+  FailureOr<ast::LetStmt *> parseLetStmt();
+
+  //===--------------------------------------------------------------------===//
+  // Creation+Analysis
+  //===--------------------------------------------------------------------===//
+
+  //===--------------------------------------------------------------------===//
+  // Decls
+
+  /// Try to create a pattern decl with the given components, returning the
+  /// Pattern on success.
+  FailureOr<ast::PatternDecl *> createPatternDecl(llvm::SMRange loc,
+                                                  const ast::Name *name,
+                                                  Optional<uint16_t> benefit,
+                                                  bool hasBoundedRecursion,
+                                                  ast::CompoundStmt *body);
+
+  /// Try to create a variable decl with the given components, returning the
+  /// Variable on success.
+  FailureOr<ast::VariableDecl *>
+  createVariableDecl(StringRef name, llvm::SMRange loc, ast::Expr *initializer,
+                     ArrayRef<ast::ConstraintRef> constraints);
+
+  /// Validate the constraints used to constraint a variable decl.
+  /// `inferredType` is the type of the variable inferred by the constraints
+  /// within the list, and is updated to the most refined type as determined by
+  /// the constraints. Returns success if the constraint list is valid, failure
+  /// otherwise.
+  LogicalResult
+  validateVariableConstraints(ArrayRef<ast::ConstraintRef> constraints,
+                              ast::Type &inferredType);
+  /// Validate a single reference to a constraint. `inferredType` contains the
+  /// currently inferred variabled type and is refined within the type defined
+  /// by the constraint. Returns success if the constraint is valid, failure
+  /// otherwise.
+  LogicalResult validateVariableConstraint(const ast::ConstraintRef &ref,
+                                           ast::Type &inferredType);
+  LogicalResult validateTypeConstraintExpr(const ast::Expr *typeExpr);
+  LogicalResult validateTypeRangeConstraintExpr(const ast::Expr *typeExpr);
+
+  //===--------------------------------------------------------------------===//
+  // Exprs
+
+  FailureOr<ast::DeclRefExpr *> createDeclRefExpr(llvm::SMRange loc,
+                                                  ast::Decl *decl);
+  FailureOr<ast::DeclRefExpr *>
+  createInlineVariableExpr(ast::Type type, StringRef name, llvm::SMRange loc,
+                           ArrayRef<ast::ConstraintRef> constraints);
+  FailureOr<ast::MemberAccessExpr *>
+  createMemberAccessExpr(ast::Expr *parentExpr, StringRef name,
+                         llvm::SMRange loc);
+
+  /// Validate the member access `name` into the given parent expression. On
+  /// success, this also returns the type of the member accessed.
+  FailureOr<ast::Type> validateMemberAccess(ast::Expr *parentExpr,
+                                            StringRef name, llvm::SMRange loc);
+
+  //===--------------------------------------------------------------------===//
+  // Stmts
+
+  FailureOr<ast::EraseStmt *> createEraseStmt(llvm::SMRange loc,
+                                              ast::Expr *rootOp);
+
+  //===--------------------------------------------------------------------===//
+  // Lexer Utilities
+  //===--------------------------------------------------------------------===//
+
+  /// If the current token has the specified kind, consume it and return true.
+  /// If not, return false.
+  bool consumeIf(Token::Kind kind) {
+    if (curToken.isNot(kind))
+      return false;
+    consumeToken(kind);
+    return true;
+  }
+
+  /// Advance the current lexer onto the next token.
+  void consumeToken() {
+    assert(curToken.isNot(Token::eof, Token::error) &&
+           "shouldn't advance past EOF or errors");
+    curToken = lexer.lexToken();
+  }
+
+  /// Advance the current lexer onto the next token, asserting what the expected
+  /// current token is. This is preferred to the above method because it leads
+  /// to more self-documenting code with better checking.
+  void consumeToken(Token::Kind kind) {
+    assert(curToken.is(kind) && "consumed an unexpected token");
+    consumeToken();
+  }
+
+  /// Consume the specified token if present and return success. On failure,
+  /// output a diagnostic and return failure.
+  LogicalResult parseToken(Token::Kind kind, const Twine &msg) {
+    if (curToken.getKind() != kind)
+      return emitError(curToken.getLoc(), msg);
+    consumeToken();
+    return success();
+  }
+  LogicalResult emitError(llvm::SMRange loc, const Twine &msg) {
+    lexer.emitError(loc, msg);
+    return failure();
+  }
+  LogicalResult emitError(const Twine &msg) {
+    return emitError(curToken.getLoc(), msg);
+  }
+  LogicalResult emitErrorAndNote(llvm::SMRange loc, const Twine &msg,
+                                 llvm::SMRange noteLoc, const Twine &note) {
+    lexer.emitErrorAndNote(loc, msg, noteLoc, note);
+    return failure();
+  }
+
+  //===--------------------------------------------------------------------===//
+  // Fields
+  //===--------------------------------------------------------------------===//
+
+  /// The owning AST context.
+  ast::Context &ctx;
+
+  /// The lexer of this parser.
+  Lexer lexer;
+
+  /// The current token within the lexer.
+  Token curToken;
+
+  /// The most recently defined decl scope.
+  ast::DeclScope *curDeclScope;
+  llvm::SpecificBumpPtrAllocator<ast::DeclScope> scopeAllocator;
+
+  /// The current context of the parser.
+  ParserContext parserContext = ParserContext::Global;
+
+  /// The include directories of the parser context.
+  const std::vector<std::string> &includeDirs;
+
+  /// Cached types to simplify verification and expression creation.
+  ast::Type valueTy, valueRangeTy;
+  ast::Type typeTy, typeRangeTy;
+};
+} // namespace
+
+FailureOr<ast::Module *> Parser::parseModule() {
+  llvm::SMLoc moduleLoc = curToken.getStartLoc();
+  pushDeclScope();
+
+  // Parse the top-level decls of the module.
+  SmallVector<ast::Decl *> decls;
+  if (failed(parseModuleBody(decls)))
+    return popDeclScope(), failure();
+
+  popDeclScope();
+  return ast::Module::create(ctx, moduleLoc, decls);
+}
+
+LogicalResult Parser::parseModuleBody(SmallVector<ast::Decl *> &decls) {
+  while (curToken.isNot(Token::eof)) {
+    if (curToken.is(Token::directive)) {
+      if (failed(parseDirective(decls)))
+        return failure();
+      continue;
+    }
+
+    FailureOr<ast::Decl *> decl = parseTopLevelDecl();
+    if (failed(decl))
+      return failure();
+    decls.push_back(*decl);
+  }
+  return success();
+}
+
+LogicalResult Parser::convertExpressionTo(
+    ast::Expr *&expr, ast::Type type,
+    function_ref<void(ast::Diagnostic &diag)> noteAttachFn) {
+  ast::Type exprType = expr->getType();
+  if (exprType == type)
+    return success();
+
+  auto emitConvertError = [&]() -> ast::InFlightDiagnostic {
+    ast::InFlightDiagnostic diag = ctx.getDiagEngine().emitError(
+        expr->getLoc(), llvm::formatv("unable to convert expression of type "
+                                      "`{0}` to the expected type of "
+                                      "`{1}`",
+                                      exprType, type));
+    if (noteAttachFn)
+      noteAttachFn(*diag);
+    return diag;
+  };
+
+  if (auto exprOpType = exprType.dyn_cast<ast::OperationType>()) {
+    // Two operation types are compatible if they have the same name, or if the
+    // expected type is more general.
+    if (auto opType = type.dyn_cast<ast::OperationType>()) {
+      if (opType.getName())
+        return emitConvertError();
+      return success();
+    }
+
+    // An operation can always convert to a ValueRange.
+    if (type == valueRangeTy) {
+      expr = ast::MemberAccessExpr::create(ctx, expr->getLoc(), expr,
+                                           "$results", valueRangeTy);
+      return success();
+    }
+
+    // Allow conversion to a single value by constraining the result range.
+    if (type == valueTy) {
+      expr = ast::MemberAccessExpr::create(ctx, expr->getLoc(), expr,
+                                           "$results", valueTy);
+      return success();
+    }
+    return emitConvertError();
+  }
+
+  // FIXME: Decide how to allow/support converting a single result to multiple,
+  // and multiple to a single result. For now, we just allow Single->Range,
+  // but this isn't something really supported in the PDL dialect. We should
+  // figure out some way to support both.
+  if ((exprType == valueTy || exprType == valueRangeTy) &&
+      (type == valueTy || type == valueRangeTy))
+    return success();
+  if ((exprType == typeTy || exprType == typeRangeTy) &&
+      (type == typeTy || type == typeRangeTy))
+    return success();
+
+  return emitConvertError();
+}
+
+//===----------------------------------------------------------------------===//
+// Directives
+
+LogicalResult Parser::parseDirective(SmallVector<ast::Decl *> &decls) {
+  StringRef directive = curToken.getSpelling();
+  if (directive == "#include")
+    return parseInclude(decls);
+
+  return emitError("unknown directive `" + directive + "`");
+}
+
+LogicalResult Parser::parseInclude(SmallVector<ast::Decl *> &decls) {
+  llvm::SMRange loc = curToken.getLoc();
+  consumeToken(Token::directive);
+
+  // Parse the file being included.
+  if (!curToken.isString())
+    return emitError(loc,
+                     "expected string file name after `include` directive");
+  llvm::SMRange fileLoc = curToken.getLoc();
+  std::string filenameStr = curToken.getStringValue();
+  StringRef filename = filenameStr;
+  consumeToken();
+
+  // Check the type of include. If ending with `.pdll`, this is another pdl file
+  // to be parsed along with the current module.
+  if (filename.endswith(".pdll")) {
+    if (failed(lexer.pushInclude(filename)))
+      return emitError(fileLoc,
+                       "unable to open include file `" + filename + "`");
+
+    // If we added the include successfully, parse it into the current module.
+    // Make sure to save the current token so that we can restore it when we
+    // finish parsing the nested file.
+    Token oldToken = curToken;
+    curToken = lexer.lexToken();
+    LogicalResult result = parseModuleBody(decls);
+    curToken = oldToken;
+    return result;
+  }
+
+  return emitError(fileLoc, "expected include filename to end with `.pdll`");
+}
+
+//===----------------------------------------------------------------------===//
+// Decls
+
+FailureOr<ast::Decl *> Parser::parseTopLevelDecl() {
+  FailureOr<ast::Decl *> decl;
+  switch (curToken.getKind()) {
+  case Token::kw_Pattern:
+    decl = parsePatternDecl();
+    break;
+  default:
+    return emitError("expected top-level declaration, such as a `Pattern`");
+  }
+  if (failed(decl))
+    return failure();
+
+  // If the decl has a name, add it to the current scope.
+  if (const ast::Name *name = (*decl)->getName()) {
+    if (failed(checkDefineNamedDecl(*name)))
+      return failure();
+    curDeclScope->add(*decl);
+  }
+  return decl;
+}
+
+FailureOr<ast::Decl *> Parser::parsePatternDecl() {
+  llvm::SMRange loc = curToken.getLoc();
+  consumeToken(Token::kw_Pattern);
+  llvm::SaveAndRestore<ParserContext> saveCtx(parserContext,
+                                              ParserContext::PatternMatch);
+
+  // Check for an optional identifier for the pattern name.
+  const ast::Name *name = nullptr;
+  if (curToken.is(Token::identifier)) {
+    name = &ast::Name::create(ctx, curToken.getSpelling(), curToken.getLoc());
+    consumeToken(Token::identifier);
+  }
+
+  // TODO: Parse any pattern metadata.
+  Optional<uint16_t> benefit;
+  bool hasBoundedRecursion = false;
+
+  // Parse the pattern body.
+  ast::CompoundStmt *body;
+
+  if (curToken.isNot(Token::l_brace))
+    return emitError("expected `{` to start pattern body");
+  FailureOr<ast::CompoundStmt *> bodyResult = parseCompoundStmt();
+  if (failed(bodyResult))
+    return failure();
+  body = *bodyResult;
+
+  // Verify the body of the pattern.
+  auto bodyIt = body->begin(), bodyE = body->end();
+  for (; bodyIt != bodyE; ++bodyIt) {
+    // Break when we've found the rewrite statement.
+    if (isa<ast::OpRewriteStmt>(*bodyIt))
+      break;
+  }
+  if (bodyIt == bodyE) {
+    return emitError(loc,
+                     "expected Pattern body to terminate with an operation "
+                     "rewrite statement, such as `erase`");
+  }
+  if (std::next(bodyIt) != bodyE) {
+    return emitError((*std::next(bodyIt))->getLoc(),
+                     "Pattern body was terminated by an operation "
+                     "rewrite statement, but found trailing statements");
+  }
+
+  return createPatternDecl(loc, name, benefit, hasBoundedRecursion, body);
+}
+
+FailureOr<ast::Expr *> Parser::parseTypeConstraintExpr() {
+  consumeToken(Token::less);
+
+  FailureOr<ast::Expr *> typeExpr = parseExpr();
+  if (failed(typeExpr) ||
+      failed(parseToken(Token::greater,
+                        "expected '>' after variable type constraint")))
+    return failure();
+  return typeExpr;
+}
+
+LogicalResult Parser::checkDefineNamedDecl(const ast::Name &name) {
+  assert(curDeclScope && "defining decl outside of a decl scope");
+  if (ast::Decl *lastDecl = curDeclScope->lookup(name.getName())) {
+    return emitErrorAndNote(
+        name.getLoc(), "`" + name.getName() + "` has already been defined",
+        lastDecl->getName()->getLoc(), "see previous definition here");
+  }
+  return success();
+}
+
+FailureOr<ast::VariableDecl *>
+Parser::defineVariableDecl(StringRef name, llvm::SMRange nameLoc,
+                           ast::Type type, ast::Expr *initExpr,
+                           ArrayRef<ast::ConstraintRef> constraints) {
+  assert(curDeclScope && "defining variable outside of decl scope");
+  const ast::Name &nameDecl = ast::Name::create(ctx, name, nameLoc);
+
+  // If the name of the variable indicates a special variable, we don't add it
+  // to the scope. This variable is local to the definition point.
+  if (name.empty() || name == "_") {
+    return ast::VariableDecl::create(ctx, nameDecl, type, initExpr,
+                                     constraints);
+  }
+  if (failed(checkDefineNamedDecl(nameDecl)))
+    return failure();
+
+  auto *varDecl =
+      ast::VariableDecl::create(ctx, nameDecl, type, initExpr, constraints);
+  curDeclScope->add(varDecl);
+  return varDecl;
+}
+
+FailureOr<ast::VariableDecl *>
+Parser::defineVariableDecl(StringRef name, llvm::SMRange nameLoc,
+                           ast::Type type,
+                           ArrayRef<ast::ConstraintRef> constraints) {
+  return defineVariableDecl(name, nameLoc, type, /*initExpr=*/nullptr,
+                            constraints);
+}
+
+LogicalResult Parser::parseVariableDeclConstraintList(
+    SmallVectorImpl<ast::ConstraintRef> &constraints) {
+  Optional<llvm::SMRange> typeConstraint;
+  auto parseSingleConstraint = [&] {
+    FailureOr<ast::ConstraintRef> constraint =
+        parseConstraint(typeConstraint, constraints);
+    if (failed(constraint))
+      return failure();
+    constraints.push_back(*constraint);
+    return success();
+  };
+
+  // Check to see if this is a single constraint, or a list.
+  if (!consumeIf(Token::l_square))
+    return parseSingleConstraint();
+
+  do {
+    if (failed(parseSingleConstraint()))
+      return failure();
+  } while (consumeIf(Token::comma));
+  return parseToken(Token::r_square, "expected `]` after constraint list");
+}
+
+FailureOr<ast::ConstraintRef>
+Parser::parseConstraint(Optional<llvm::SMRange> &typeConstraint,
+                        ArrayRef<ast::ConstraintRef> existingConstraints) {
+  auto parseTypeConstraint = [&](ast::Expr *&typeExpr) -> LogicalResult {
+    if (typeConstraint)
+      return emitErrorAndNote(
+          curToken.getLoc(),
+          "the type of this variable has already been constrained",
+          *typeConstraint, "see previous constraint location here");
+    FailureOr<ast::Expr *> constraintExpr = parseTypeConstraintExpr();
+    if (failed(constraintExpr))
+      return failure();
+    typeExpr = *constraintExpr;
+    typeConstraint = typeExpr->getLoc();
+    return success();
+  };
+
+  llvm::SMRange loc = curToken.getLoc();
+  switch (curToken.getKind()) {
+  case Token::kw_Attr: {
+    consumeToken(Token::kw_Attr);
+
+    // Check for a type constraint.
+    ast::Expr *typeExpr = nullptr;
+    if (curToken.is(Token::less) && failed(parseTypeConstraint(typeExpr)))
+      return failure();
+    return ast::ConstraintRef(
+        ast::AttrConstraintDecl::create(ctx, loc, typeExpr), loc);
+  }
+  case Token::kw_Op: {
+    consumeToken(Token::kw_Op);
+
+    // Parse an optional operation name.
+    FailureOr<ast::OpNameDecl *> opName = parseWrappedOperationName();
+    if (failed(opName))
+      return failure();
+
+    return ast::ConstraintRef(ast::OpConstraintDecl::create(ctx, loc, *opName),
+                              loc);
+  }
+  case Token::kw_Type:
+    consumeToken(Token::kw_Type);
+    return ast::ConstraintRef(ast::TypeConstraintDecl::create(ctx, loc), loc);
+  case Token::kw_TypeRange:
+    consumeToken(Token::kw_TypeRange);
+    return ast::ConstraintRef(ast::TypeRangeConstraintDecl::create(ctx, loc),
+                              loc);
+  case Token::kw_Value: {
+    consumeToken(Token::kw_Value);
+
+    // Check for a type constraint.
+    ast::Expr *typeExpr = nullptr;
+    if (curToken.is(Token::less) && failed(parseTypeConstraint(typeExpr)))
+      return failure();
+
+    return ast::ConstraintRef(
+        ast::ValueConstraintDecl::create(ctx, loc, typeExpr), loc);
+  }
+  case Token::kw_ValueRange: {
+    consumeToken(Token::kw_ValueRange);
+
+    // Check for a type constraint.
+    ast::Expr *typeExpr = nullptr;
+    if (curToken.is(Token::less) && failed(parseTypeConstraint(typeExpr)))
+      return failure();
+
+    return ast::ConstraintRef(
+        ast::ValueRangeConstraintDecl::create(ctx, loc, typeExpr), loc);
+  }
+  case Token::identifier: {
+    StringRef constraintName = curToken.getSpelling();
+    consumeToken(Token::identifier);
+
+    // Lookup the referenced constraint.
+    ast::Decl *cstDecl = curDeclScope->lookup<ast::Decl>(constraintName);
+    if (!cstDecl) {
+      return emitError(loc, "unknown reference to constraint `" +
+                                constraintName + "`");
+    }
+
+    // Handle a reference to a proper constraint.
+    if (auto *cst = dyn_cast<ast::ConstraintDecl>(cstDecl))
+      return ast::ConstraintRef(cst, loc);
+
+    return emitErrorAndNote(
+        loc, "invalid reference to non-constraint", cstDecl->getLoc(),
+        "see the definition of `" + constraintName + "` here");
+  }
+  default:
+    break;
+  }
+  return emitError(loc, "expected identifier constraint");
+}
+
+//===----------------------------------------------------------------------===//
+// Exprs
+
+FailureOr<ast::Expr *> Parser::parseExpr() {
+  if (curToken.is(Token::underscore))
+    return parseUnderscoreExpr();
+
+  // Parse the LHS expression.
+  FailureOr<ast::Expr *> lhsExpr;
+  switch (curToken.getKind()) {
+  case Token::identifier:
+    lhsExpr = parseIdentifierExpr();
+    break;
+  default:
+    return emitError("expected expression");
+  }
+  if (failed(lhsExpr))
+    return failure();
+
+  // Check for an operator expression.
+  while (true) {
+    switch (curToken.getKind()) {
+    case Token::dot:
+      lhsExpr = parseMemberAccessExpr(*lhsExpr);
+      break;
+    default:
+      return lhsExpr;
+    }
+    if (failed(lhsExpr))
+      return failure();
+  }
+}
+
+FailureOr<ast::Expr *> Parser::parseDeclRefExpr(StringRef name,
+                                                llvm::SMRange loc) {
+  ast::Decl *decl = curDeclScope->lookup(name);
+  if (!decl)
+    return emitError(loc, "undefined reference to `" + name + "`");
+
+  return createDeclRefExpr(loc, decl);
+}
+
+FailureOr<ast::Expr *> Parser::parseIdentifierExpr() {
+  StringRef name = curToken.getSpelling();
+  llvm::SMRange nameLoc = curToken.getLoc();
+  consumeToken();
+
+  // Check to see if this is a decl ref expression that defines a variable
+  // inline.
+  if (consumeIf(Token::colon)) {
+    SmallVector<ast::ConstraintRef> constraints;
+    if (failed(parseVariableDeclConstraintList(constraints)))
+      return failure();
+    ast::Type type;
+    if (failed(validateVariableConstraints(constraints, type)))
+      return failure();
+    return createInlineVariableExpr(type, name, nameLoc, constraints);
+  }
+
+  return parseDeclRefExpr(name, nameLoc);
+}
+
+FailureOr<ast::Expr *> Parser::parseMemberAccessExpr(ast::Expr *parentExpr) {
+  llvm::SMRange loc = curToken.getLoc();
+  consumeToken(Token::dot);
+
+  // Parse the member name.
+  Token memberNameTok = curToken;
+  if (memberNameTok.isNot(Token::identifier, Token::integer) &&
+      !memberNameTok.isKeyword())
+    return emitError(loc, "expected identifier or numeric member name");
+  StringRef memberName = memberNameTok.getSpelling();
+  consumeToken();
+
+  return createMemberAccessExpr(parentExpr, memberName, loc);
+}
+
+FailureOr<ast::OpNameDecl *> Parser::parseOperationName() {
+  llvm::SMRange loc = curToken.getLoc();
+
+  // Handle the case of an no operation name.
+  if (curToken.isNot(Token::identifier) && !curToken.isKeyword())
+    return ast::OpNameDecl::create(ctx, llvm::SMRange());
+
+  StringRef name = curToken.getSpelling();
+  consumeToken();
+
+  // Otherwise, this is a literal operation name.
+  if (failed(parseToken(Token::dot, "expected `.` after dialect namespace")))
+    return failure();
+
+  if (curToken.isNot(Token::identifier) && !curToken.isKeyword())
+    return emitError("expected operation name after dialect namespace");
+
+  name = StringRef(name.data(), name.size() + 1);
+  do {
+    name = StringRef(name.data(), name.size() + curToken.getSpelling().size());
+    loc.End = curToken.getEndLoc();
+    consumeToken();
+  } while (curToken.isAny(Token::identifier, Token::dot) ||
+           curToken.isKeyword());
+  return ast::OpNameDecl::create(ctx, ast::Name::create(ctx, name, loc));
+}
+
+FailureOr<ast::OpNameDecl *> Parser::parseWrappedOperationName() {
+  if (!consumeIf(Token::less))
+    return ast::OpNameDecl::create(ctx, llvm::SMRange());
+
+  FailureOr<ast::OpNameDecl *> opNameDecl = parseOperationName();
+  if (failed(opNameDecl))
+    return failure();
+
+  if (failed(parseToken(Token::greater, "expected `>` after operation name")))
+    return failure();
+  return opNameDecl;
+}
+
+FailureOr<ast::Expr *> Parser::parseUnderscoreExpr() {
+  StringRef name = curToken.getSpelling();
+  llvm::SMRange nameLoc = curToken.getLoc();
+  consumeToken(Token::underscore);
+
+  // Underscore expressions require a constraint list.
+  if (failed(parseToken(Token::colon, "expected `:` after `_` variable")))
+    return failure();
+
+  // Parse the constraints for the expression.
+  SmallVector<ast::ConstraintRef> constraints;
+  if (failed(parseVariableDeclConstraintList(constraints)))
+    return failure();
+
+  ast::Type type;
+  if (failed(validateVariableConstraints(constraints, type)))
+    return failure();
+  return createInlineVariableExpr(type, name, nameLoc, constraints);
+}
+
+//===----------------------------------------------------------------------===//
+// Stmts
+
+FailureOr<ast::Stmt *> Parser::parseStmt(bool expectTerminalSemicolon) {
+  FailureOr<ast::Stmt *> stmt;
+  switch (curToken.getKind()) {
+  case Token::kw_erase:
+    stmt = parseEraseStmt();
+    break;
+  case Token::kw_let:
+    stmt = parseLetStmt();
+    break;
+  default:
+    stmt = parseExpr();
+    break;
+  }
+  if (failed(stmt) ||
+      (expectTerminalSemicolon &&
+       failed(parseToken(Token::semicolon, "expected `;` after statement"))))
+    return failure();
+  return stmt;
+}
+
+FailureOr<ast::CompoundStmt *> Parser::parseCompoundStmt() {
+  llvm::SMLoc startLoc = curToken.getStartLoc();
+  consumeToken(Token::l_brace);
+
+  // Push a new block scope and parse any nested statements.
+  pushDeclScope();
+  SmallVector<ast::Stmt *> statements;
+  while (curToken.isNot(Token::r_brace)) {
+    FailureOr<ast::Stmt *> statement = parseStmt();
+    if (failed(statement))
+      return popDeclScope(), failure();
+    statements.push_back(*statement);
+  }
+  popDeclScope();
+
+  // Consume the end brace.
+  llvm::SMRange location(startLoc, curToken.getEndLoc());
+  consumeToken(Token::r_brace);
+
+  return ast::CompoundStmt::create(ctx, location, statements);
+}
+
+FailureOr<ast::EraseStmt *> Parser::parseEraseStmt() {
+  llvm::SMRange loc = curToken.getLoc();
+  consumeToken(Token::kw_erase);
+
+  // Parse the root operation expression.
+  FailureOr<ast::Expr *> rootOp = parseExpr();
+  if (failed(rootOp))
+    return failure();
+
+  return createEraseStmt(loc, *rootOp);
+}
+
+FailureOr<ast::LetStmt *> Parser::parseLetStmt() {
+  llvm::SMRange loc = curToken.getLoc();
+  consumeToken(Token::kw_let);
+
+  // Parse the name of the new variable.
+  llvm::SMRange varLoc = curToken.getLoc();
+  if (curToken.isNot(Token::identifier) && !curToken.isDependentKeyword()) {
+    // `_` is a reserved variable name.
+    if (curToken.is(Token::underscore)) {
+      return emitError(varLoc,
+                       "`_` may only be used to define \"inline\" variables");
+    }
+    return emitError(varLoc,
+                     "expected identifier after `let` to name a new variable");
+  }
+  StringRef varName = curToken.getSpelling();
+  consumeToken();
+
+  // Parse the optional set of constraints.
+  SmallVector<ast::ConstraintRef> constraints;
+  if (consumeIf(Token::colon) &&
+      failed(parseVariableDeclConstraintList(constraints)))
+    return failure();
+
+  // Parse the optional initializer expression.
+  ast::Expr *initializer = nullptr;
+  if (consumeIf(Token::equal)) {
+    FailureOr<ast::Expr *> initOrFailure = parseExpr();
+    if (failed(initOrFailure))
+      return failure();
+    initializer = *initOrFailure;
+
+    // Check that the constraints are compatible with having an initializer,
+    // e.g. type constraints cannot be used with initializers.
+    for (ast::ConstraintRef constraint : constraints) {
+      LogicalResult result =
+          TypeSwitch<const ast::Node *, LogicalResult>(constraint.constraint)
+              .Case<ast::AttrConstraintDecl, ast::ValueConstraintDecl,
+                    ast::ValueRangeConstraintDecl>([&](const auto *cst) {
+                if (auto *typeConstraintExpr = cst->getTypeExpr()) {
+                  return emitError(
+                      constraint.referenceLoc,
+                      "type constraints are not permitted on variables with "
+                      "initializers");
+                }
+                return success();
+              })
+              .Default(success());
+      if (failed(result))
+        return failure();
+    }
+  }
+
+  FailureOr<ast::VariableDecl *> varDecl =
+      createVariableDecl(varName, varLoc, initializer, constraints);
+  if (failed(varDecl))
+    return failure();
+  return ast::LetStmt::create(ctx, loc, *varDecl);
+}
+
+//===----------------------------------------------------------------------===//
+// Creation+Analysis
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+// Decls
+
+FailureOr<ast::PatternDecl *>
+Parser::createPatternDecl(llvm::SMRange loc, const ast::Name *name,
+                          Optional<uint16_t> benefit, bool hasBoundedRecursion,
+                          ast::CompoundStmt *body) {
+  return ast::PatternDecl::create(ctx, loc, name, benefit, hasBoundedRecursion,
+                                  body);
+}
+
+FailureOr<ast::VariableDecl *>
+Parser::createVariableDecl(StringRef name, llvm::SMRange loc,
+                           ast::Expr *initializer,
+                           ArrayRef<ast::ConstraintRef> constraints) {
+  // The type of the variable, which is expected to be inferred by either a
+  // constraint or an initializer expression.
+  ast::Type type;
+  if (failed(validateVariableConstraints(constraints, type)))
+    return failure();
+
+  if (initializer) {
+    // Update the variable type based on the initializer, or try to convert the
+    // initializer to the existing type.
+    if (!type)
+      type = initializer->getType();
+    else if (ast::Type mergedType = type.refineWith(initializer->getType()))
+      type = mergedType;
+    else if (failed(convertExpressionTo(initializer, type)))
+      return failure();
+
+    // Otherwise, if there is no initializer check that the type has already
+    // been resolved from the constraint list.
+  } else if (!type) {
+    return emitErrorAndNote(
+        loc, "unable to infer type for variable `" + name + "`", loc,
+        "the type of a variable must be inferable from the constraint "
+        "list or the initializer");
+  }
+
+  // Try to define a variable with the given name.
+  FailureOr<ast::VariableDecl *> varDecl =
+      defineVariableDecl(name, loc, type, initializer, constraints);
+  if (failed(varDecl))
+    return failure();
+
+  return *varDecl;
+}
+
+LogicalResult
+Parser::validateVariableConstraints(ArrayRef<ast::ConstraintRef> constraints,
+                                    ast::Type &inferredType) {
+  for (const ast::ConstraintRef &ref : constraints)
+    if (failed(validateVariableConstraint(ref, inferredType)))
+      return failure();
+  return success();
+}
+
+LogicalResult Parser::validateVariableConstraint(const ast::ConstraintRef &ref,
+                                                 ast::Type &inferredType) {
+  ast::Type constraintType;
+  if (const auto *cst = dyn_cast<ast::AttrConstraintDecl>(ref.constraint)) {
+    if (const ast::Expr *typeExpr = cst->getTypeExpr()) {
+      if (failed(validateTypeConstraintExpr(typeExpr)))
+        return failure();
+    }
+    constraintType = ast::AttributeType::get(ctx);
+  } else if (const auto *cst =
+                 dyn_cast<ast::OpConstraintDecl>(ref.constraint)) {
+    constraintType = ast::OperationType::get(ctx, cst->getName());
+  } else if (isa<ast::TypeConstraintDecl>(ref.constraint)) {
+    constraintType = typeTy;
+  } else if (isa<ast::TypeRangeConstraintDecl>(ref.constraint)) {
+    constraintType = typeRangeTy;
+  } else if (const auto *cst =
+                 dyn_cast<ast::ValueConstraintDecl>(ref.constraint)) {
+    if (const ast::Expr *typeExpr = cst->getTypeExpr()) {
+      if (failed(validateTypeConstraintExpr(typeExpr)))
+        return failure();
+    }
+    constraintType = valueTy;
+  } else if (const auto *cst =
+                 dyn_cast<ast::ValueRangeConstraintDecl>(ref.constraint)) {
+    if (const ast::Expr *typeExpr = cst->getTypeExpr()) {
+      if (failed(validateTypeRangeConstraintExpr(typeExpr)))
+        return failure();
+    }
+    constraintType = valueRangeTy;
+  } else {
+    llvm_unreachable("unknown constraint type");
+  }
+
+  // Check that the constraint type is compatible with the current inferred
+  // type.
+  if (!inferredType) {
+    inferredType = constraintType;
+  } else if (ast::Type mergedTy = inferredType.refineWith(constraintType)) {
+    inferredType = mergedTy;
+  } else {
+    return emitError(ref.referenceLoc,
+                     llvm::formatv("constraint type `{0}` is incompatible "
+                                   "with the previously inferred type `{1}`",
+                                   constraintType, inferredType));
+  }
+  return success();
+}
+
+LogicalResult Parser::validateTypeConstraintExpr(const ast::Expr *typeExpr) {
+  ast::Type typeExprType = typeExpr->getType();
+  if (typeExprType != typeTy) {
+    return emitError(typeExpr->getLoc(),
+                     "expected expression of `Type` in type constraint");
+  }
+  return success();
+}
+
+LogicalResult
+Parser::validateTypeRangeConstraintExpr(const ast::Expr *typeExpr) {
+  ast::Type typeExprType = typeExpr->getType();
+  if (typeExprType != typeRangeTy) {
+    return emitError(typeExpr->getLoc(),
+                     "expected expression of `TypeRange` in type constraint");
+  }
+  return success();
+}
+
+//===----------------------------------------------------------------------===//
+// Exprs
+
+FailureOr<ast::DeclRefExpr *> Parser::createDeclRefExpr(llvm::SMRange loc,
+                                                        ast::Decl *decl) {
+  // Check the type of decl being referenced.
+  ast::Type declType;
+  if (auto *varDecl = dyn_cast<ast::VariableDecl>(decl))
+    declType = varDecl->getType();
+  else
+    return emitError(loc, "invalid reference to `" +
+                              decl->getName()->getName() + "`");
+
+  return ast::DeclRefExpr::create(ctx, loc, decl, declType);
+}
+
+FailureOr<ast::DeclRefExpr *>
+Parser::createInlineVariableExpr(ast::Type type, StringRef name,
+                                 llvm::SMRange loc,
+                                 ArrayRef<ast::ConstraintRef> constraints) {
+  FailureOr<ast::VariableDecl *> decl =
+      defineVariableDecl(name, loc, type, constraints);
+  if (failed(decl))
+    return failure();
+  return ast::DeclRefExpr::create(ctx, loc, *decl, type);
+}
+
+FailureOr<ast::MemberAccessExpr *>
+Parser::createMemberAccessExpr(ast::Expr *parentExpr, StringRef name,
+                               llvm::SMRange loc) {
+  // Validate the member name for the given parent expression.
+  FailureOr<ast::Type> memberType = validateMemberAccess(parentExpr, name, loc);
+  if (failed(memberType))
+    return failure();
+
+  return ast::MemberAccessExpr::create(ctx, loc, parentExpr, name, *memberType);
+}
+
+FailureOr<ast::Type> Parser::validateMemberAccess(ast::Expr *parentExpr,
+                                                  StringRef name,
+                                                  llvm::SMRange loc) {
+  ast::Type parentType = parentExpr->getType();
+  if (ast::OperationType opType = parentType.dyn_cast<ast::OperationType>()) {
+    // $results is a special member access representing all of the results.
+    // TODO: Should we have special AST expressions for these? How does the
+    // user reference these in the language itself?
+    if (name == "$results")
+      return valueRangeTy;
+  }
+  return emitError(
+      loc,
+      llvm::formatv("invalid member access `{0}` on expression of type `{1}`",
+                    name, parentType));
+}
+
+//===----------------------------------------------------------------------===//
+// Stmts
+
+FailureOr<ast::EraseStmt *> Parser::createEraseStmt(llvm::SMRange loc,
+                                                    ast::Expr *rootOp) {
+  // Check that root is an Operation.
+  ast::Type rootType = rootOp->getType();
+  if (!rootType.isa<ast::OperationType>())
+    return emitError(rootOp->getLoc(), "expected `Op` expression");
+
+  return ast::EraseStmt::create(ctx, loc, rootOp);
+}
+
+//===----------------------------------------------------------------------===//
+// Parser
+//===----------------------------------------------------------------------===//
+
+FailureOr<ast::Module *>
+mlir::pdll::parsePDLAST(ast::Context &ctx, llvm::SourceMgr &sourceMgr,
+                        const std::vector<std::string> &includeDirs) {
+  Parser parser(ctx, sourceMgr, includeDirs);
+  return parser.parseModule();
+}

mlir/test/mlir-pdll/Parser/directive-failure.pdll

+// RUN: not mlir-pdll %s -split-input-file 2>&1  | FileCheck %s
+
+// CHECK: unknown directive `#foo`
+#foo
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// Include
+//===----------------------------------------------------------------------===//
+
+// CHECK: expected string file name after `include` directive
+#include <>
+
+// -----
+
+// CHECK: unable to open include file `unknown_file.pdll`
+#include "unknown_file.pdll"
+
+// -----
+
+// CHECK: expected include filename to end with `.pdll`
+#include "unknown_file.foo"

mlir/test/mlir-pdll/Parser/expr-failure.pdll

+// RUN: not mlir-pdll %s -split-input-file 2>&1 | FileCheck %s
+
+//===----------------------------------------------------------------------===//
+// Reference Expr
+//===----------------------------------------------------------------------===//
+
+Pattern {
+  // CHECK: expected identifier constraint
+  let foo = Foo: ;
+}
+
+// -----
+
+Pattern {
+  // CHECK: undefined reference to `bar`
+  let foo = bar;
+}
+
+// -----
+
+Pattern FooPattern {
+  erase _: Op;
+}
+
+Pattern {
+  // CHECK: invalid reference to `FooPattern`
+  let foo = FooPattern;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected `:` after `_` variable
+  let foo = _;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected identifier constraint
+  let foo = _: ;
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// Member Access Expr
+//===----------------------------------------------------------------------===//
+
+Pattern {
+  // CHECK: expected identifier or numeric member name
+  let root: Op;
+  erase root.<>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: invalid member access `unknown_result` on expression of type `Op`
+  let root: Op;
+  erase root.unknown_result;
+}

mlir/test/mlir-pdll/Parser/include.pdll

+// RUN: mlir-pdll %s -I %S | FileCheck %s
+
+Pattern BeforeIncludedPattern {
+  erase _: Op;
+}
+
+#include "include/included.pdll"
+
+Pattern AfterIncludedPattern {
+  erase _: Op;
+}
+
+// CHECK: PatternDecl {{.*}} Name<BeforeIncludedPattern>
+// CHECK: PatternDecl {{.*}} Name<IncludedPattern>
+// CHECK: PatternDecl {{.*}} Name<AfterIncludedPattern>

mlir/test/mlir-pdll/Parser/include/included.pdll

+// This file is included by 'include.pdll' as part of testing include files.
+
+Pattern IncludedPattern {
+  erase _: Op;
+}

mlir/test/mlir-pdll/Parser/lit.local.cfg

+config.suffixes = ['.pdll']
+config.excludes = ['include']

mlir/test/mlir-pdll/Parser/pattern-failure.pdll

+// RUN: not mlir-pdll %s -split-input-file 2>&1  | FileCheck %s
+
+// CHECK: expected `{` to start pattern body
+Pattern }
+
+// -----
+
+// CHECK: :6:9: error: `Foo` has already been defined
+// CHECK: :5:9: note: see previous definition here
+Pattern Foo { erase root: Op; }
+Pattern Foo { erase root: Op; }
+
+// -----
+
+// CHECK: expected Pattern body to terminate with an operation rewrite statement
+Pattern {
+  let value: Value;
+}
+
+// -----
+
+// CHECK: Pattern body was terminated by an operation rewrite statement, but found trailing statements
+Pattern {
+  erase root: Op;
+  let value: Value;
+}

mlir/test/mlir-pdll/Parser/pattern.pdll

+// RUN: mlir-pdll %s -I %S -split-input-file | FileCheck %s
+
+// CHECK: Module
+// CHECK: `-PatternDecl
+// CHECK:   `-CompoundStmt
+// CHECK:     `-EraseStmt
+Pattern {
+  erase _: Op;
+}
+
+// -----
+
+// CHECK: Module
+// CHECK: `-PatternDecl {{.*}} Name<NamedPattern>
+Pattern NamedPattern {
+  erase _: Op;
+}

mlir/test/mlir-pdll/Parser/stmt-failure.pdll

+// RUN: not mlir-pdll %s -split-input-file 2>&1 | FileCheck %s
+
+// CHECK: expected top-level declaration, such as a `Pattern`
+10
+
+// -----
+
+Pattern {
+  // CHECK: expected `;` after statement
+  erase _: Op
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// `erase`
+//===----------------------------------------------------------------------===//
+
+Pattern {
+  // CHECK: expected expression
+  erase;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected `Op` expression
+  erase _: Attr;
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// `let`
+//===----------------------------------------------------------------------===//
+
+Pattern {
+  // CHECK: expected identifier after `let` to name a new variable
+  let 5;
+}
+
+// -----
+
+Pattern {
+  // CHECK: `_` may only be used to define "inline" variables
+  let _;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression
+  let foo: Attr<>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression of `Type` in type constraint
+  let foo: Attr<_: Attr>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected '>' after variable type constraint
+  let foo: Attr<_: Type{};
+}
+
+// -----
+
+Pattern {
+  // CHECK: the type of this variable has already been constrained
+  let foo: [Attr<_: Type>, Attr<_: Type];
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected `.` after dialect namespace
+  let foo: Op<builtin>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected operation name after dialect namespace
+  let foo: Op<builtin.>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected `>` after operation name
+  let foo: Op<builtin.func<;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression
+  let foo: Value<>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression of `Type` in type constraint
+  let foo: Value<_: Attr>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected '>' after variable type constraint
+  let foo: Value<_: Type{};
+}
+
+// -----
+
+Pattern {
+  // CHECK: the type of this variable has already been constrained
+  let foo: [Value<_: Type>, Value<_: Type];
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression
+  let foo: ValueRange<10>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression of `TypeRange` in type constraint
+  let foo: ValueRange<_: Type>;
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected '>' after variable type constraint
+  let foo: ValueRange<_: Type{};
+}
+
+// -----
+
+Pattern {
+  // CHECK: the type of this variable has already been constrained
+  let foo: [ValueRange<_: Type>, ValueRange<_: Type];
+}
+
+// -----
+
+Pattern {
+  // CHECK: unknown reference to constraint `UnknownConstraint`
+  let foo: UnknownConstraint;
+}
+
+// -----
+
+Pattern Foo {
+  erase root: Op;
+}
+
+Pattern {
+  // CHECK: invalid reference to non-constraint
+  let foo: Foo;
+}
+
+// -----
+
+Pattern {
+  // CHECK: constraint type `Attr` is incompatible with the previously inferred type `Value`
+  let foo: [Value, Attr];
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected `]` after constraint list
+  let foo: [Attr[];
+}
+
+// -----
+
+Pattern {
+  // CHECK: expected expression
+  let foo: Attr = ;
+}
+
+// -----
+
+Pattern {
+  // CHECK: type constraints are not permitted on variables with initializers
+  let foo: ValueRange<_: Type> = _: Op;
+}
+
+// -----
+
+Pattern {
+  // CHECK: unable to infer type for variable `foo`
+  // CHECK: note: the type of a variable must be inferable from the constraint list or the initializer
+  let foo;
+}
+
+// -----
+
+Pattern {
+  // CHECK: unable to convert expression of type `Attr` to the expected type of `Value`
+  let foo: Value = _: Attr;
+}
+
+// -----
+
+Pattern {
+  // CHECK: :7:7: error: `foo` has already been defined
+  // CHECK: :6:7: note: see previous definition here
+  let foo: Attr;
+  let foo: Attr;
+}

mlir/test/mlir-pdll/Parser/stmt.pdll

+// RUN: mlir-pdll %s -I %S -split-input-file | FileCheck %s
+
+//===----------------------------------------------------------------------===//
+// CompoundStmt
+//===----------------------------------------------------------------------===//
+
+// CHECK: Module
+// CHECK: CompoundStmt
+// CHECK:   |-LetStmt
+// CHECK:   `-EraseStmt
+Pattern {
+  let root: Op;
+  erase root;
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// EraseStmt
+//===----------------------------------------------------------------------===//
+
+// CHECK: Module
+// CHECK: EraseStmt
+// CHECK:   `-DeclRefExpr {{.*}} Type<Op>
+Pattern {
+  erase _: Op;
+}
+
+// -----
+
+//===----------------------------------------------------------------------===//
+// LetStmt
+//===----------------------------------------------------------------------===//
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<attrVar> Type<Attr>
+// CHECK:     `Constraints`
+// CHECK:       `-AttrConstraintDecl
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<Op>
+// CHECK:     `Constraints`
+// CHECK:       `-OpConstraintDecl
+// CHECK:         `-OpNameDecl
+Pattern {
+  let attrVar: Attr;
+  let var: Op;
+  erase var;
+}
+
+// -----
+
+// Check for proper refinement between constraint types.
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<Op<dialect.op>>
+// CHECK:     `Constraints`
+// CHECK:       `-OpConstraintDecl
+// CHECK:         `-OpNameDecl
+// CHECK:       `-OpConstraintDecl
+// CHECK:         `-OpNameDecl {{.*}} Name<dialect.op>
+Pattern {
+  let var: [Op, Op<dialect.op>];
+  erase var;
+}
+
+// -----
+
+// Check for proper conversion between initializer and constraint type.
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<Op<dialect.op>>
+// CHECK:     `-DeclRefExpr {{.*}} Type<Op<dialect.op>>
+// CHECK:       `-VariableDecl {{.*}} Name<input>
+// CHECK:     `Constraints`
+// CHECK:       `-OpConstraintDecl
+// CHECK:         `-OpNameDecl
+Pattern {
+  let input: Op<dialect.op>;
+  let var: Op = input;
+  erase var;
+}
+
+// -----
+
+// Check for proper conversion between initializer and constraint type.
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<Value>
+// CHECK:     `-MemberAccessExpr {{.*}} Member<$results> Type<Value>
+// CHECK:       `-DeclRefExpr {{.*}} Type<Op<dialect.op>>
+// CHECK:         `-VariableDecl {{.*}} Name<input>
+// CHECK:     `Constraints`
+// CHECK:       `-ValueConstraintDecl
+Pattern {
+  let input: Op<dialect.op>;
+  let var: Value = input;
+  erase _: Op;
+}
+
+// -----
+
+// Check for proper conversion between initializer and constraint type.
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<ValueRange>
+// CHECK:     `-MemberAccessExpr {{.*}} Member<$results> Type<ValueRange>
+// CHECK:       `-DeclRefExpr {{.*}} Type<Op<dialect.op>>
+// CHECK:         `-VariableDecl {{.*}} Name<input>
+// CHECK:     `Constraints`
+// CHECK:       `-ValueRangeConstraintDecl
+Pattern {
+  let input: Op<dialect.op>;
+  let var: ValueRange = input;
+  erase _: Op;
+}
+
+// -----
+
+// Check for proper handling of type constraints.
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<Value>
+// CHECK:     `Constraints`
+// CHECK:       `-ValueConstraintDecl
+// CHECK:         `-DeclRefExpr {{.*}} Type<Type>
+// CHECK:           `-VariableDecl {{.*}} Name<_> Type<Type>
+// CHECK:             `Constraints`
+// CHECK:               `-TypeConstraintDecl
+Pattern {
+  let var: Value<_: Type>;
+  erase _: Op;
+}
+
+// -----
+
+// Check for proper handling of type constraints.
+
+// CHECK: Module
+// CHECK: LetStmt
+// CHECK:   `-VariableDecl {{.*}} Name<var> Type<ValueRange>
+// CHECK:     `Constraints`
+// CHECK:       `-ValueRangeConstraintDecl
+// CHECK:         `-DeclRefExpr {{.*}} Type<TypeRange>
+// CHECK:           `-VariableDecl {{.*}} Name<_> Type<TypeRange>
+// CHECK:             `Constraints`
+// CHECK:               `-TypeRangeConstraintDecl
+Pattern {
+  let var: ValueRange<_: TypeRange>;
+  erase _: Op;
+}

mlir/tools/mlir-pdll/mlir-pdll.cpp

+//===- mlir-pdll.cpp - MLIR PDLL frontend -----------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#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/Parser/Parser.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/InitLLVM.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/ToolOutputFile.h"
+
+using namespace mlir;
+using namespace mlir::pdll;
+
+//===----------------------------------------------------------------------===//
+// main
+//===----------------------------------------------------------------------===//
+
+/// The desired output type.
+enum class OutputType {
+  AST,
+};
+
+static LogicalResult
+processBuffer(raw_ostream &os, std::unique_ptr<llvm::MemoryBuffer> chunkBuffer,
+              OutputType outputType, std::vector<std::string> &includeDirs) {
+  llvm::SourceMgr sourceMgr;
+  sourceMgr.setIncludeDirs(includeDirs);
+  sourceMgr.AddNewSourceBuffer(std::move(chunkBuffer), llvm::SMLoc());
+
+  ast::Context astContext;
+  FailureOr<ast::Module *> module =
+      parsePDLAST(astContext, sourceMgr, includeDirs);
+  if (failed(module))
+    return failure();
+
+  switch (outputType) {
+  case OutputType::AST:
+    (*module)->print(os);
+    break;
+  }
+
+  return success();
+}
+
+int main(int argc, char **argv) {
+  llvm::cl::opt<std::string> inputFilename(
+      llvm::cl::Positional, llvm::cl::desc("<input file>"), llvm::cl::init("-"),
+      llvm::cl::value_desc("filename"));
+
+  llvm::cl::opt<std::string> outputFilename(
+      "o", llvm::cl::desc("Output filename"), llvm::cl::value_desc("filename"),
+      llvm::cl::init("-"));
+
+  llvm::cl::list<std::string> includeDirs(
+      "I", llvm::cl::desc("Directory of include files"),
+      llvm::cl::value_desc("directory"), llvm::cl::Prefix);
+
+  llvm::cl::opt<bool> splitInputFile(
+      "split-input-file",
+      llvm::cl::desc("Split the input file into pieces and process each "
+                     "chunk independently"),
+      llvm::cl::init(false));
+  llvm::cl::opt<enum OutputType> outputType(
+      "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")));
+
+  llvm::InitLLVM y(argc, argv);
+  llvm::cl::ParseCommandLineOptions(argc, argv, "PDLL Frontend");
+
+  // Set up the input file.
+  std::string errorMessage;
+  std::unique_ptr<llvm::MemoryBuffer> inputFile =
+      openInputFile(inputFilename, &errorMessage);
+  if (!inputFile) {
+    llvm::errs() << errorMessage << "\n";
+    return 1;
+  }
+
+  // Set up the output file.
+  std::unique_ptr<llvm::ToolOutputFile> outputFile =
+      openOutputFile(outputFilename, &errorMessage);
+  if (!outputFile) {
+    llvm::errs() << errorMessage << "\n";
+    return 1;
+  }
+
+  // The split-input-file mode is a very specific mode that slices the file
+  // up into small pieces and checks each independently.
+  auto processFn = [&](std::unique_ptr<llvm::MemoryBuffer> chunkBuffer,
+                       raw_ostream &os) {
+    return processBuffer(os, std::move(chunkBuffer), outputType, includeDirs);
+  };
+  if (splitInputFile) {
+    if (failed(splitAndProcessBuffer(std::move(inputFile), processFn,
+                                     outputFile->os())))
+      return 1;
+  } else if (failed(processFn(std::move(inputFile), outputFile->os()))) {
+    return 1;
+  }
+  outputFile->keep();
+  return 0;
+}

utils/bazel/llvm-project-overlay/mlir/BUILD.bazel

deps = [
         ":AllPassesAndDialects",
         ":IR",
         ":MlirReduceLib",
         ":Pass",
         "//llvm:Support",
         "//mlir/test:TestDialect",
     ],
 )
+
+cc_library(
+    name = "PDLLAST",
+    srcs = glob(
+        [
+            "lib/Tools/PDLL/AST/*.cpp",
+            "lib/Tools/PDLL/AST/*.h",
+        ],
+    ),
+    hdrs = glob(["include/mlir/Tools/PDLL/AST/*.h"]),
+    includes = ["include"],
+    deps = [
+        "//llvm:Support",
+        "//llvm:TableGen",
+        "//mlir:Support",
+    ],
+)
+
+cc_library(
+    name = "PDLLParser",
+    srcs = glob(
+        [
+            "lib/Tools/PDLL/Parser/*.cpp",
+            "lib/Tools/PDLL/Parser/*.h",
+        ],
+    ),
+    hdrs = glob(["include/mlir/Tools/PDLL/Parser/*.h"]),
+    includes = ["include"],
+    deps = [
+        ":PDLLAST",
+        ":Support",
+        ":TableGen",
+        "//llvm:Support",
+        "//llvm:TableGen",
+    ],
+)
+
+cc_binary(
+    name = "mlir-pdll",
+    srcs = [
+        "tools/mlir-pdll/mlir-pdll.cpp",
+    ],
+    deps = [
+        ":PDLLAST",
+        ":PDLLParser",
+        ":Support",
+        "//llvm:Support",
+        "//llvm:config",
+    ],
+)