ExprMutator refactor & Normalizer

include/tvm/ir/expr.h

@@ -241,6 +241,7 @@ class GlobalVar : public RelayExpr {
   TVM_DLL explicit GlobalVar(String name_hint);
 
   TVM_DEFINE_OBJECT_REF_METHODS(GlobalVar, RelayExpr, GlobalVarNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(GlobalVarNode);
 };
 
 // PrimExprs that are useful as runtime containers.

include/tvm/relax/block_builder.h

@@ -44,39 +44,43 @@ class BlockBuilder;
  */
 class BlockBuilderNode : public Object {
  public:
-  BlockBuilderNode(std::shared_ptr<NameTable> name_table) : name_table_(name_table) {}
+  BlockBuilderNode();
 
   ~BlockBuilderNode();
 
-  BlockBuilderNode() { name_table_ = std::make_shared<NameTable>(); }
-
   /*! \brief Begin to build a DataflowBlock. */
   void BeginDataflowBlock();
+
   /*! \brief Begin to build a BindingBlock. */
   void BeginBindingBlock();
+
   /*!
    * \brief End building a BindingBlock.
    * \return The BindingBlock being built.
    */
   BindingBlock EndBlock();
+
   /*!
    * \brief Check if the block being built is DataflowBlock or not.
    * \return A boolean that indicates if the block being built is DataflowBlock or not.
    */
   inline bool CurrentBlockIsDataFlow() { return CurrentFrame()->is_dataflow; }
+
   /*!
    * \brief Emits an Expr, and returns the variable it is bound to.
    * \param expr The Expr to be emitted.
    * \param name_hint Name hint for the bound variable.
    * \return The new variable that \p expr is bound to.
    */
   virtual Var Emit(const Expr& expr, std::string name_hint = "");
+
   /*!
    * \brief Emits a variable binding, and returns the bound Var.
    * \param binding The variable binding.
    * \return The bound variable.
    */
   virtual Var Emit(const VarBinding& binding);
+
   /*!
    * \brief Emit a MatchShape.
    * \param value The value of the MatchShape to be emitted.
@@ -85,49 +89,57 @@ class BlockBuilderNode : public Object {
    * \return The variable bound to the MatchShape.
    */
   Var EmitMatchShape(const Expr& value, const Array<PrimExpr>& pattern, std::string name_hint = "");
+
   /*!
    * \brief Emit a MatchShape binding.
    * \param binding The MatchShape binding to be emitted.
    * \return The variable bound to the MatchShape.
    */
   Var EmitMatchShape(const MatchShape& binding);
+
   /*!
    * \brief Generate an output for the current dataflow block.
    * \param output The output variable of the block.
    * \param name_hint Name hint for the bound variable.
    * \return The variable bound to \p output.
    */
   Var EmitOutput(const Expr& output, std::string name_hint = "");
+
   /*!
    * \brief Generate an output for the current dataflow block.
    * \param binding The output binding to output.
    * \return The variable bound to \p output.
    */
   Var EmitOutput(const VarBinding& binding);
+
   /*!
-   * \brief Lookup a var in the binding table \p var_map_.
+   * \brief Lookup a var in the binding table \p binding_table_.
    * \param var The input var.
    * \return The Expr bound to the input \p var.
    */
-  Expr LookupVar(const Var& var);
+  Expr LookupBinding(const Var& var);
+
   /*!
    * \brief Check if two shape expressions can be proven equal at compile time.
    * \param lhs The input lhs shape.
    * \param rhs The input rhs shape.
    * \return Whether we can prove lhs shape is the same as the rhs shape.
    */
   bool CanProveShapeEqual(const Expr& lhs, const Expr& rhs);
+
   /*!
-   * \brief Normalize an Expr to complete its shape and type.
-   * \param expr The input expr.
-   * \return The expr with normalized shape and type.
+   * \brief Convert an expression to A-normal form, and try to eagerly infer types and shapes.
+   * \param expr The input expression.
+   * \return The normalized expression.
    */
   Expr Normalize(const Expr& expr);
+
   /*!
-   * \brief Create a BlockBuilder.
-   * \return The created BlockBuilder.
+   * \brief Get the name table for generating unique names.
+   *
+   * \return The name table.
    */
-  TVM_DLL static BlockBuilder Create();
+  NameTable* name_table();
 
   void VisitAttrs(AttrVisitor* v) {}
 
@@ -150,26 +162,45 @@ class BlockBuilderNode : public Object {
     Array<Binding> bindings;
     bool is_dataflow;
   };
+
+  /*!
+   * \brief Utility class for performing IR normalization (conversion to ANF, eager forward shape
+   * and type inference).
+   */
+  class ExprNormalizer;
+
   friend class BlockBuilder;
+
   /*!
    * \brief Get the current block frame.
    * \return The current block frame.
    */
   BlockFrame* CurrentFrame();
+
   /*! \brief A stack to store block frames. */
   std::stack<BlockFrame> block_stack_;
+
   /*! \brief A diagnostic context for reporting errors. */
   DiagnosticContext diag_ctx_ = DiagnosticContext::Default(IRModule({}, {}));
+
   /*! \brief A binding table that maps var to value. */
-  // TODO(@yuchen, @altanh): make var_map_ scoped, and decide if it should be in the builder
-  std::unordered_map<Id, Expr, ObjectPtrHash, ObjectPtrEqual> var_map_;
+  std::unordered_map<Id, Expr, ObjectPtrHash, ObjectPtrEqual> binding_table_;
+
   /*! \brief A name table to get unique names for IR construction. */
-  std::shared_ptr<NameTable> name_table_;
+  std::unique_ptr<NameTable> name_table_;
+
+  /*! \brief The internal normalizer used for ANF conversion. */
+  std::unique_ptr<ExprNormalizer> normalizer_;
 };
 
 class BlockBuilder : public ObjectRef {
  public:
-  TVM_DLL explicit BlockBuilder(std::shared_ptr<NameTable> name_table);
+  /*!
+   * \brief Create a BlockBuilder.
+   * \return The created BlockBuilder.
+   */
+  TVM_DLL static BlockBuilder Create();
+
   TVM_DEFINE_MUTABLE_OBJECT_REF_METHODS(BlockBuilder, ObjectRef, BlockBuilderNode);
 };
 

include/tvm/relax/expr.h

@@ -79,6 +79,7 @@ class ShapeExpr : public Expr {
  public:
   TVM_DLL explicit ShapeExpr(Array<PrimExpr> values, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(ShapeExpr, Expr, ShapeExprNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(ShapeExprNode);
 };
 
 /*! \brief The variable class for all Relax bindings. */
@@ -131,6 +132,7 @@ class Var : public Expr {
   TVM_DLL explicit Var(Id vid, runtime::Optional<Expr> shape_annotation,
                        runtime::Optional<Type> type_annotation, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(Var, Expr, VarNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(VarNode); 
 };
 
 /*! \brief A sub-type of the variable node used to mark dataflow variables from
@@ -175,6 +177,7 @@ class DataflowVar : public Var {
                                runtime::Optional<Type> type_annotation, Span span = Span());
 
   TVM_DEFINE_OBJECT_REF_METHODS(DataflowVar, Var, DataflowVarNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(DataflowVarNode);
 };
 
 /*! \brief The base class of a variable binding in Relax. */
@@ -235,6 +238,7 @@ class MatchShape : public Binding {
   TVM_DLL explicit MatchShape(Expr value, Array<PrimExpr> pattern,
                               Var var, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(MatchShape, Binding, MatchShapeNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(MatchShapeNode);
 };
 
 class VarBinding;
@@ -266,6 +270,7 @@ class VarBinding : public Binding {
  public:
   TVM_DLL explicit VarBinding(Var var, Expr value, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(VarBinding, Binding, VarBindingNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(VarBindingNode);
 };
 
 class BindingBlock;
@@ -296,6 +301,7 @@ class BindingBlock : public ObjectRef {
  public:
   TVM_DLL explicit BindingBlock(Array<Binding> bindings, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(BindingBlock, ObjectRef, BindingBlockNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(BindingBlockNode);
 };
 
 class DataflowBlock;
@@ -315,6 +321,7 @@ class DataflowBlock : public BindingBlock {
  public:
   TVM_DLL explicit DataflowBlock(Array<Binding> bindings, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(DataflowBlock, BindingBlock, DataflowBlockNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(DataflowBlockNode);
 };
 
 /*! \brief A sequence of blocks followed by an expression.
@@ -356,6 +363,7 @@ class SeqExpr : public Expr {
  public:
   TVM_DLL explicit SeqExpr(Array<BindingBlock> blocks, Expr body, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(SeqExpr, Expr, SeqExprNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(SeqExprNode);
 };
 
 /*! \brief A Relax function, eventually to replace the current Relay function definition. */
@@ -411,6 +419,7 @@ class Function : public Expr {
   TVM_DLL explicit Function(runtime::Optional<GlobalVar> name, Array<Var> params, Expr body,
                             Type ret_type, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(Function, Expr, FunctionNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(FunctionNode);
 };
 
 /*! \brief The extern function, which can represent packed function. */
@@ -440,6 +449,7 @@ class ExternFunc : public Expr {
  public:
   TVM_DLL ExternFunc(String global_symbol, Span span = Span());
   TVM_DEFINE_OBJECT_REF_METHODS(ExternFunc, Expr, ExternFuncNode);
+  TVM_DEFINE_OBJECT_REF_COW_METHOD(ExternFuncNode);
 };
 
 }  // namespace relax

include/tvm/relax/expr_functor.h

@@ -178,16 +178,7 @@ void PostOrderVisit(const Expr& node, std::function<void(const Expr&)> fvisit);
 class ExprMutator : public ExprFunctor<Expr(const Expr&)> {
  public:
   ExprMutator() {
-    name_table_ = std::make_shared<NameTable>();
-    builder_ = BlockBuilder(name_table_);
-  }
-
-  /*!
-   * \brief Mutate is alias for VisitExpr
-   * \return expr.
-   */
-  Expr Mutate(const Expr& expr) {
-    return this->VisitExpr(expr);
+    builder_ = BlockBuilder::Create();
   }
 
   Expr VisitExpr(const Expr& expr) override;
@@ -218,47 +209,60 @@ class ExprMutator : public ExprFunctor<Expr(const Expr&)> {
   virtual void VisitVarBinding(const VarBinding& binding);
   virtual void VisitMatchShape(const MatchShape& binding);
 
+  /*!
+   * \brief Rewrite the var definition site.
+   * \param var The var to be visited.
+   * \return The var after post-order rewritten.
+   * \note VisitExpr_(const VarNode*) will only visit the usage site of an Var
+   */
+  virtual Var VisitVarDef(const Var& var);
+
   virtual BindingBlock VisitBindingBlock(const BindingBlock& block);
   virtual BindingBlock VisitDataflowBlock(const DataflowBlock& block);
 
  protected:
-  Expr MutateWithPrologue(const Expr& expr, bool is_dataflow);
+  class ExprNormalizer;
 
-  /*! \brief Look up the value of a variable. If the variable is bound, then returns the bound
-   *  value. Otherwise, returns the rewritten expression for the variable.
+  /*!
+   * \brief Rewrite the expr with a new scope, used in a Function's body and the branches of If.
+   * \param expr The expr to be visited.
+   * \return The expr after visiting.
    */
-  Expr LookupVar(Var var);
+  Expr VisitWithNewScope(const Expr& expr);
 
-  inline void UpdateMemo(Expr pre, Expr post) {
-    if (const VarNode* var = pre.as<VarNode>()) {
-      var_memo_[var->vid] = post;
-    } else {
-      expr_memo_[pre] = post;
-    }
-  }
+  /*!
+   * \brief Look up the value bound to a variable.
+   * \param var The var to be looked up.
+   * \return The value bound to the input \p var.
+   */
+  Expr LookupBinding(const Var& var);
 
-  inline Optional<Expr> LookupMemo(Expr pre) {
-    if (pre.as<VarNode>()) {
-      Id vid = Downcast<Var>(pre)->vid;
-      if (var_memo_.count(vid)) {
-        return var_memo_[vid];
-      }
-    } else {
-      if (expr_memo_.count(pre)) {
-        return expr_memo_[pre];
-      }
-    }
-    return NullOpt;
+  /*!
+   * \brief Post-order rewrite a node and normalize.
+   * \param T The node type to be rewritten.
+   * \param op The node to be rewritten.
+   * \return The node after post rewritten.
+   */
+  template <typename T>
+  Expr VisitExprPostOrder_(const T* op) {
+    return builder_->Normalize(ExprMutator::VisitExpr_(op));
   }
 
-  /*! \brief Variable memoization table using Id equality */
-  std::unordered_map<Id, Expr, ObjectPtrHash, ObjectPtrEqual> var_memo_;
-
-  /*! \brief Expr memoization table using pointer equality */
-  std::unordered_map<Expr, Expr, ObjectPtrHash, ObjectPtrEqual> expr_memo_;
+  /*!
+   * \brief Create a new var with specified shape and type if it's original shape or type does not
+   * match with the specified ones.
+   * \param var The var to be updated.
+   * \param shape The specified shape.
+   * \param type The specified type.
+   * \return The var filled with \p shape and \p type.
+   */
+  Var WithShapeAndType(Var var, Optional<ObjectRef> shape, Type type);
 
-  std::shared_ptr<NameTable> name_table_;
+  /*! \brief Internal block builder to emit bindings during rewriting. */
   BlockBuilder builder_;
+
+  /*! \brief Remap a var to a new var in use-site. */
+  std::unordered_map<Id, Var, ObjectPtrHash, ObjectPtrEqual> var_remap_;
 };
 
 // TODO(@yuchen, @altan): Refactor to enforce dataflow mutator only rewrite stuff in dataflow blocks